AU2005230209A1 - Antimicrobial compositions and methods for their use - Google Patents

Description

WO 2005/097094 PCT/AU2005/000511 Antimicrobial Compositions and Methods for Their Use This invention relates to the treatment or prevention of skin and ear tissue infections in mammals involving application of a wash composition comprising a polymeric biguanide 5 or a bis(biguanide) compound, a chelating agent and a buffering agent. The invention further relates to compositions useful in such treatment or prevention. Treatment of infections of the skin and epithelial lined body cavities and particularly the external ear, can be very difficult as these areas attract antimicrobial resistant micro 10 organisms in humans and warm blooded animals. The antimicrobial resistance may be developed as a consequence of repeated exposure to antimicrobial drugs during treatment of recurrent infections and subsequent selection of resistant strains, or may be a result of invasion by a micro-organism which has inherent antimicrobial resistance. 15 The commonly encountered micro-organisms that infect the ears of mammals include the bacteria Staphylococcus spp. Enterobacteriacae such as Escherichia coli, Klebsiella spp, Proteus mirabilis, Proteus vulgaris and Pseudomonads such as Pseudomonas aeruginosa. These micro-organisms are known to thrive in cavities, such as ear canals, and sometimes even benefit from antimicrobial treatment, possibly by removal of other susceptible micro 20 organisms competing for the same environment. An example of such a phenomenon is the dramatic overgrowth of Malassezia after reduction in Pseudononas numbers (Foster, DeBoer 1998). Ear infections are often difficult to treat as inflammatory cells, biological proteins, 25 enzymes, DNA and other chemicals and biological compounds in a purulent exudate around an infection in the ear decrease or inactivate the antimicrobial and biocidal action of drugs prescribed for treatment of the infection. Many drugs that are prescribed to treat infections are neuro-toxic and thus ototoxic (Rohn et. al. 1993).

WO 2005/097094 PCT/AU2005/000511 -2 There is a need for a simple and effective treatment for ear infections that is rapid and active at low levels, below ototoxic levels. There is also a need for treatments that have a broad action in reversing the resistance spectrum of an infection to antimicrobial drugs. 5 A combination of a chelating agent, ethylenediaminetetraacetic acid (EDTA), and a buffering agent, tris(hydroxymethyl)aminomethane (Tris), has previously been used as an ear wash in dogs. It is known that this combination has some antimicrobial activity, but the primary advantage of the Tris-EDTA combination is that it improves the susceptibility of micro-organisms, particularly micro-organisms with antimicrobial resistance, to the 10 effects of antibiotics (Ashworth and Nelson, 1990; Green, 1984; Neer, 1982; Foster and DeBoer, 1998; Farcia, 1993; Farcia, 1997; Gotthelf, 2003). However, in the order of 10 to 15 minutes exposure of Tris-EDTA to the ear canal may be required (Paterson, 2003). Farcia (1997) found that using a non-proprietary Tris-EDTA solution was effective after 10 minutes. Some in vitro models require hours for these beneficial effects (Woolley et. 15 al., 1983a, 1983b) although Gotthelf (2003) found an in vitro lowering of the minimum inhibitory concentration (MIC) effect of Tris-EDTA could occur at 5 and 30 minutes. Such prolonged times may be difficult in domestic animals such as dogs and cats that shake their heads to remove liquid from their ears upon administration of the ear wash. 20 Current Tris-EDTA flush solutions have a minimal effect on Gram positive organisms and no effect on yeasts like Candida and Malassezia due to differences in cell walls (Foster and DeBoer, 1998; Sparkes et. al., 1994). Patterson (2003) advises "In fact prolonged use of EDTA-tris like many water based [ear] cleaners can predispose to Malassezia infection". 25 WO 03/086332 has described the use of a preserved Tris-EDTA formulation as a wash solution. In this case, the chosen preservative was non-ionic and selected to allow conformance with USP preservative efficacy testing. This solution could be used alone as an antiseptic wash or may be used as a carrier for an antibiotic. 30 WO 2005/097094 PCT/AU2005/000511 Tris is not known to have any biological activity, however, it is known that EDTA chelates calcium and magnesium ions in water. It is speculated that EDTA is able to bind calcium and magnesium ions in bacterial cell walls, weakening the cell walls and thereby improving the effects of subsequent treatment with antibiotics. 5 Biguanide compounds are known antiseptics and have been used as topical antiseptics, in contact lens solutions and as disinfectants for wastewater and its containers. Biguanides include bis(biguanides) such as chlorhexidine and alexidine and polymeric biguanides such as polyhexamethylene biguanide (PHMB) and others as described in the literature (East et. 10 al., 1997; Ikeda et. al., 1984). The bis(biguanide) chlorhexidine has been used in many antiseptic applications. Ototoxicity has occasionally been reported when chlorhexidine was used as a presurgical antisceptic in and around the ear in man and animals. However, there are conflicting 15 reports of the ototoxicity of chlorhexidine (Willoughby K., 1989; Merchant S.R., 1994; Aursnes, J., 1981a and 1981b). Some studies have shown that compositions containing chlorhexidine are ototoxic especially in concentrations as high as 2%, this is particularly so when the tympanic membrane has been ruptured (Harvey et. al., 2001; Merchant, 1994). Other studies have shown no ototoxic effects when 0.2% chlorhexidine was placed in the 20 external ear of dogs with ruptured tympanic membranes (Merchant et. al., 1992). The combination of chlorhexidine with ethanol or quaternary ammonium compounds such as centrimide, enhances ototoxicity (Harvey et. al., 2001). Great care must be taken with administration of chlorhexidine to the ear to ensure that the tympanic membrane is intact, the concentration is below ototoxic amounts and that no additives are present that may 25 enhance its ototoxic effect. Chlorhexidine (0.01%) has also been used in combination with Tris-EDTA as a bladder instillation in patients with spinal cord trauma requiring intermittent catheterisation (Harper, 1987; Pearman, 1988). However, 0.02% chlorhexidine compositions were found 30 to cause chemical cystitis resulting in haematuria (Pearman, 1988).

WO 2005/097094 PCT/AU2005/000511 -4 Advantageously, the present inventor has found that a combination of a biguanide compound with a buffering agent and a chelating agent may provide a rapid and effective treatment for ear infections and infections of other tissues such as skin and may improve the susceptibility of micro-organisms to the effects of antibiotics. 5 According to an aspect of the present invention there is provided a method of inhibiting, treating or preventing infections of the skin in a mammal, comprising topical administration of an effective amount of a composition comprising: (i) a chelating agent, 10 (ii) a buffering agent, and (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, to the skin of the mammal. 15 According to another aspect of the invention, there is provided a pharmaceutical or veterinary composition comprising: (i) a chelating agent, (ii) a buffering agent, and (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or 20 pharmaceutically acceptable salts thereof; with the proviso that component (iii) is not chlorhexidine. According to a further aspect, there is provided a use of (i) a chelating agent, 25 (ii) a buffering agent, and (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, in the manufacture of a medicament for the treatment or prophylaxis of infections of the skin of a mammal. 30 WO 2005/097094 PCT/AU2005/000511 -5 The invention is particularly useful for inhibiting, treating or preventing infections of the external ear. Suitable mammals include any mammal prone to skin infections such as ear infections, for 5 example humans, domestic animals such as pets and agriculturally useful animals, such as sheep, cattle, pigs and horses. Particularly preferred mammals are humans and pets, such as cats and dogs, especially preferred mammals are dogs, especially long-haired, pendulous-eared breeds of dog. 10 As used herein, the term "external ear" refers to the pinna or auricle and the auditory canal or meatus of the ear. The method and composition of the invention are particularly useful for inhibiting or treating infections caused by yeasts, Gram positive and/or Gram negative bacteria, 15 especially those bacteria that have at least some resistance to the effects of antibiotics. The method and composition is particularly useful for treating or inhibiting infections caused by Staphylococcus spp such as Staphylococcus aureus, Staphylococcus intermedius, Enterobacteriacae such as Escherichia coli, Klebsiella spp, Proteus spp such as Proteus mirabilis and Pseudomonads such as Pseudomonas aeruginosa, Streptococcus spp. and 20 yeasts such as Malassezia pachydermatis and Candida albicans and fungi such as Aspergillus spp. Preferably, the methods and compositions are used for treating or inhibiting infections caused by Pseudomonas aeruginosa, Staphylococcus intermedius and Malassezia pachydermatis. 25 A biguanide compound comprises a group of the formula: HN-C-NH-C-NH- (I NH N H or a salt or tautomer thereof.

WO 2005/097094 PCT/AU2005/000511 -6 A bis(biguanide) comprises two groups of formula (I) or salts thereof linked by a divalent bridging group and a polymeric biguanide comprises 3 or more groups of formula (I) or salts thereof, each linked by a divalent bridging group. 5 Preferred bis(biguanides) are those having the following formula: HH H H H H 2 X1--- C--N--C-N-Z-N--C-N--C--N-X NH NH NH NH (II) (11)2 or a tautomer thereof, wherein Z is a divalent bridging group and X1 and X2 are 10 independently selected from optionally substituted alkyl, optionally substituted aryl, optionally substituted cycloalkyl, optionally substituted heterocyclyl or optionally substituted heteroaryl or a pharmaceutically or veterinarily acceptable salt thereof. The above bis(biguanide) compounds and methods for their preparation are described, for example, in US Patent Nos. 4,670,592 and 4,952,704. Preferred bis(biguanides) include 15 chlorhexidine (commercially available from various sources such as Degussa AG of Dusseldorf, Germany), where X1 and X 2 are both 4-chlorophenyl and Z is -(CH 2

)

6 - and alexidine (commercially available from Ravensberg GmbH Chemische Fabrik, Konstanz, Germany), where X1 and X 2 are both 3-ethylhexane and Z is -(CH 2

)

6 -. 20 In a preferred embodiment the biguanide is a polymeric biguanide such as those described by East et. al., 1997 in which the biguanide appears in the polymer backbone. Especially preferred polymeric biguanides having the following formula: X3 -Z-NH-C-NH-C-NH Z-X4 Sn(III) N1H NH 25 WO 2005/097094 PCT/AU2005/000511 -.7 or a tautomer thereof, wherein Z is absent or an organic divalent bridging group and each Z may be the same or different throughout the polymer; n is at least 3, preferably 5 to 20 and

X

3 and X 4 are independently selected from -NH 2 , -NH-C(=NH)-NH-CN, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally 5 substituted heterocyclyl and optionally substituted heteroaryl; or a pharmaceutically or veterinarily acceptable salt thereof. Preferably, the molecular weight of the polymeric compound is at least 1,000 amu, more preferably between 1,000 amu and 50,000 amu. In a single composition, n may vary providing a mixture of polymeric biguanides. In some embodiments, the polymeric biguanides have a mean molecular weight in the region of 10 2,900 to 15,000, especially 3,000 to 8,000, and particularly 3,200 to 5,000, especially 3,500 to 4,500. The above polymeric biguanide compounds and methods for their preparation are described in, for example, US Patent No. 3,428,576 and East et. al., 1997. 15 Preferred polymeric biguanides in which the biguanide appears in the backbone of the polymer for use in the invention are polymeric hexamethylene biguanides such as polyhexanide or PHMB (commercially available as Vantocil, Baquacil, Arlagard, Lonzabac BG or Cosmocil) of the following formula: 20

X

3 - (CH 2

)

3 4 (CH 2

)

3 - NH-C- NH- C- NH- (CH 2

)

3

-(CH

2

)

3 - X 4 | |II NH NH (IV) or a tautomer thereof, wherein n is an integer from 3 to 500 and X 3 and X 4 are 25 independently selected from -NH 2 , -NH-C(=NH)-NH-CN, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclyl and optionally substituted heteroaryl or a pharmaceutically or veterinarily acceptable salt thereof. Preferably n has an average value of 3 to 15, more preferably 3 to 12. Most preferred are polymeric hexamethylene biguanides, commercially available, for WO 2005/097094 PCT/AU2005/000511 example, as the hydrochloride salt, from Avecia (Wilmington, Delaware, USA) under the trademark Cosmocil CQTM. In another embodiment of the invention, the polymeric biguanides are fractionated 5 polymeric biguanides where the lower molecular weight proportion of polymer is removed. In particular, polymeric biguanide compositions in which the fraction of oligomers having a value of n 5 5 is less than 2 wt%, preferably less than 0.5 wt% and most preferably is less than 0.1 wt% of the polymeric biguanides in the composition. 10 Other preferred polymeric biguanides are those with pendant biguanide groups having the formula: X5 (CH-CH 2 )m-(CH-CH 2 )p -qX6 I I

NH

2 NH C=NH ( NH X3 15 or a tautomer thereof, wherein X 3 is defined for formula III above, X 5 and X 6 are independently selected from H or X 3 , Z is absent or is a divalent bridging group, m is an integer from 1 to 10, p is 0 or an integer from 1 to 10 and q is an integer from 1 to 1000; or a pharmaceutically or veterinarily acceptable salt thereof.

WO 2005/097094 PCT/AU2005/000511 -9 Preferred polymeric biguanides having pendant biguanide groups are those described by Ikeda et. aL, 1984 in which X 5 and X 6 are hydrogen, Z is -C(O)-O-CH 2

CH

2 -C6H 4 -, X 3 is phenyl or optionally substituted phenyl, especially 4-chlorophenyl or 3,4-dichlorophenyl, m is an integer from 1 to 10, p is 0, q is an integer from 1 to 500 (homopolymer) or where 5 m is 1 to 10, p is 1 to 10 and q is 1 to 500 (co-polymer with acrylamide). The polymeric biguanides having pendant biguanide groups and methods for their preparation are described in Ikeda et. al., 1984. 10 As used herein, the term "alkyl" refers to monovalent, straight chain or branched hydrocarbon groups, having 1 to 10 carbon atoms as appropriate. For example, suitable alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, sec butyl, tert-butyl, pentyl, 2-methylpentyl, 3-methylpentyl, n-hexyl, 2-, 3- or 4-methylhexyl, 2-, 3- or 4-ethylhexyl, heptyl, octyl, nonyl and decyl. 15 As used herein, the term "cycloalkyl", refers to cyclic hydrocarbon groups. Suitable cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. 20 The term "aryl" as used herein, refers to C 6

-C

10 aromatic hydrocarbon groups such as phenyl and naphthyl. The term "heterocyclyl" or "heterocyclic", as used herein, refers to monocyclic, polycyclic, fused or conjugated cyclic hydrocarbon residues, preferably C 3

.

6 , wherein one or more 25 carbon atoms (and where appropriate, hydrogen atoms attached thereto) are replaced by a heteroatom so as to provide a non-aromatic residue. Suitable heteroatoms include, 0, N and S. Where two or more carbon atoms are replaced, this may be by two or more of the same heteroatom or by different heteroatoms. Suitable examples of heterocyclic groups may include, but are not limited to, pyrrolidinyl, pyrrolinyl, piperidyl, piperazinyl, 30 morpholino, indolinyl, imidazolidinyl, pyrazolidinyl, thiomorpholino, dioxanyl, tetrahydrofuranyl, tetrahydropyranyl, tetrahydropyrrolyl.

WO 2005/097094 PCT/AU2005/000511 - 10 The term "heteroaryl" or "heteroaromatic", as used herein, represents a stable monocyclic or bicyclic ring of up to 6 atoms in each ring, wherein at least one ring is aromatic and contains from 1 to 4 heteroatoms selected from the group consisting of 0, N and S. 5 Heteroaryl groups within the scope of this definition include, but are not limited to, acridinyl, carbazolyl, cinnolinyl, quinoxalinyl, pyrrazolyl, indolyl, benzotriazolyl, furanyl, thienyl, benzothienyl, benzofuranyl, quinolinyl, isoquinolinyl, oxazolyl, isoxazolyl, indolyl, pyrazinyl, pyridazinyl, pyridinyl, pyrimidinyl, pyrrolyl, tetrahydroquinoline. 10 Alkyl, cycloalkyl, heterocyclyl, heteroaryl and aryl groups of the invention may be optionally substituted with 1 to 5 groups selected from OH, OCi- 6 alkyl, Cl, Br, F, I, NH 2 , NH(Cp.

6 alkyl), N(C1.6alkyl)2, SH, SCi- 6 alkyl, CO 2 H, CO 2

CI

6 alkyl, CONH 2 , CONH(C 1 . 6 alkyl) or CON(Ci- 6 alkyl) 2 . 15 As used herein, the term "divalent bridging group" refers to a radical that has a valence of two and is able to bind with two other groups. Examples of suitable divalent bridging groups include, but are not limited to, -(CH 2 )t- where t is an integer from 1 to 10, -0-, -S-, a divalent saturated or aromatic carbocyclic ring or a heterocyclic or heteroaromatic ring or a combination of such divalent and/or cyclic moieties. For example a saturated C 6 cyclic 20 group would include -C 6

H

10 -, a C 6 aromatic group would include -C 6

H

4 -, a C 6 heterocyclic group would include -N / \N and a C 6 heteroaromatic would include N. 25 Other divalent bridging groups include alkylene groups (-CH 2 -)t in which one or more carbon atoms have been replaced by NH, S, 0, WO 2005/097094 PCT/AU2005/000511 - 11 0-C- or -C- U o In a preferred embodiment the divalent bridging group is -(CH 2 )t- where t is an integer from 1 to 10, especially 1 to 6, more especially 6. 5 As used herein, the term "tautomer" refers to isomeric forms of a compound which have migration of a hydrogen atom accompanied by movement of adjacent double bonds. For example, Formula (I) may tautomerise to provide different isomers according to the following equation: -NH-C-NH-C=N---NH-C-NH-C-NH- - -NH-C=N-C-NH 10 NH NH 2 NH NH

NH

2 NH When used herein, the terms Antiseptic, Antimicrobial, Preservative, Antibiotic, Disinfectant and Antibacterial shall have the meanings as prescribed in Block S. (2001) which is the internationally accepted text on the subject. 15 Thus the term "Antiseptic" as used herein refers to a substance that prevents or arrests the growth or action of microorganisms either by inhibiting their activity or by destroying them. The term is used especially for preparations applied topically to living tissue. Thus "Skin (including ear) Antiseptic" refers to a safe, non-irritating, liquid, antimicrobial 20 preparation that prevents overt skin/ear infection. The term "Preservation" as used herein refers to the process by which chemical or physical agents prevent biological deterioration of substances. The term "Preservative" as used herein refers to an agent that inhibits the growth of microorganisms capable of causing 25 biological deterioration of a substance(s)/material(s). The term "Antimicrobial" as used herein refers to the killing or suppression of the growth of microorganisms.

WO 2005/097094 PCT/AU2005/000511 - 12 The term "Antibiotic" as used herein refers to an organic chemical substance produced by a microbial organism, that has the capacity in dilute solutions to destroy or inhibit the growth of bacteria and other microorganisms. 5 The term "Antibacterial" as used herein is the same as bacteriocide and refers to an agent that kills bacteria and is applied to living tissue. The term "Disinfectant" as used herein refers to an agent that frees from infection, usually a chemical agent but sometimes a physical one. It refers to substances applied to inanimate 10 objects. Under the conditions of use, for example, at the prepared and in use pH of the compositions, the biguanide compounds are in ionic form. Suitable pharmaceutically or veterinarily acceptable salts of the ions include, but are not limited to, salts of 15 pharmaceutically acceptable inorganic acids such as hydrochloric, sulphuric, phosphoric, phosphonic, phosphanilate, nitric, carbonic, boric, sulfamic, sulfonic and hydrobromic acids, or salts of pharmaceutically acceptable organic acids such as acetic, propionic, butyric, tartaric, maleic, hydroxymaleic, fumaric, malic, citric, lactic, mucic, gluconic, benzoic, succinic, oxalic, phenylacetic, methanesulphonic, toluenesulphonic, 20 benzenesulphonic, (4-aminophenyl)phosphonic, phenylphosphonic, salicylic, sulphanilic, aspartic, glutamic, edetic, stearic, palmitic, oleic, lauric, pantothenic, tannic, ascorbic and valeric acids. Preferred salts include salts of hydrochloric, boric, sulfonic, acetic, lactic, phosphanilate, gluconic, citric and tartaric acids. 25 Preferably the chelating agent is selected from any compound that is able to sequester monovalent or polyvalent metal ions such as sodium, lithium, rubidium, cesium, calcium, magnesium, barium, cerium, cobalt, copper, iron, manganese, nickel, strontium or zinc, and is pharmaceutically or veterinarily acceptable. Suitable chelating agents include, but are not limited to amino carboxylic acids and salts thereof such as ethylene diamine 30 tetraacetic acid (EDTA), nitrilotriacetic acid, nitrilotripropionic acid, diethylenetriamine pentaacetic acid, 2-hydroxyethyl-ethylenediamine-triacetic acid, 1,6-diamino- WO 2005/097094 PCT/AU2005/000511 - 13 hexamethylene-tetraacetic acid, 1,2-diamino-cyclohexane tetraacetic acid, 0,0'-bis(2-aminoethyl)-ethyleneglycol-tetraacetic acid, 1,3-dianinopropane-tetraacetic acid, N,N-bis(2-hydroxybenzyl)ethylenediamine-N,N-diacetic acid, ethylenediamine-N,N'-diacetic acid, ethylenediamine-N,N'-dipropionic acid, 5 triethylenetetraamine hexaacetic acid, 7,19,30-trioxa-1,4,10,13,16,22,27,33 octaazabicyclo[11,11,11]pentatriacontane (0-bis-tren), ethylenediamine-N,N' bis(methylenephosphonic acid), iminodiacetic acid, NN-bis(2-hydroxyethyl)glycine (DHEG), 1,3-diamino-2-hydroxypropane-tetraacetic acid, 1,2-diaminopropane-tetraacetic acid, ethylenediamine-tetrakis(methylenephosphonic acid), 10 N-(2-hydroxyethyl)iminodiacetic acid and triethylenetetramine-hexaacetic acid, deferoxamine, dimercaprol, citrate and its salts such as zinc citrate, penicillamine and its salts and biphosphonates such as editronate or macrocyclic polyethers, such as those described in the literature (Izatt R.M. et. al., 1995). Especially preferred chelating agents are pharmaceutically and veterinarily acceptable salts and mixed salts of EDTA such as 15 disodium, trisodium, tetrasodium, dipotassium, tripotassium, lithium, dilithium, ammonium, diammonium, calcium and calcium-disodium, most preferably disodium or tetrasodium salts of EDTA, especially disodium EDTA. Buffering agents suitable for use in the invention are those that are pharmaceutically or 20 veterinarily acceptable. Preferred buffering agents include, but are not limited to, amines such as triethylamine, triethylenetetramine tetraethylethylenediamine, tetramethylenediamine and NN'-diethyl-N,N'-bis(sulfopropyl)ethylenediamine (DESPEN); piperazines such as N,N'-diethylpiperazine and piperazine-N,N' bis(alkylsulfonic acids); histadines, imidazoles, morpholines such as the 25 (N-morpholino)alkylsulfonic acids, for example, 2-morpholineethanesulfonic acid and 4 morpholinepropane sulfonic acid, aminoalcohols such as 2-aminoethanol and 2-amino-2 methyl-l-propanol (AMP) and triethanolamine, and the aminopolyols, boric acid, bicarbonate salts such as sodium bicarbonate, sodium chloride, meglumine, phosphate buffers, citrate buffers and salts thereof. Particularly preferred buffers are aminopolyols 30 such as tris(hydroxymethyl)aminomethane (also known as Tris, THAM, tromethamine and trometamol), 2-amino-2-methyl-1,3-propanediol (also known as AMPD), WO 2005/097094 PCT/AU2005/000511 -14 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol (also known as BIS-TRIS) and 1,3-bis(tris[hydroxymethyl]methylamino)propane (also known as BIS-TRIS propane and BTP), triethanolamine and salts thereof and mixtures thereof. An especially preferred buffer is Tris. In preferred embodiments, the composition should be buffered between pH 5 3 to 9, most preferably pH 5 to 8. In some embodiments, the pH is about pH 8. In other embodiments, the pH is between 6 and 7. In preferred embodiments, the bis or polymeric biguanide is present in a concentration of 0.0001% (lppm) to 10% w/w of the composition, preferably 0.001 to 5% w/w, most 10 preferably 0.001 to 2% w/w, especially between about 0.02% and 0.2% w/w. In some embodiments, including, but not limited to, use of chlorhexidine, the concentration of the bis or polymeric biguanide is in the range of greater than 0.02% and 0.5% w/w, especially 0.05 to 0.2% w/w or 0.1 to 0.2% w/w. 15 The amount of chelating agent present will depend on the nature of the chelating agent and its effectiveness in chelating ions from bacterial cell walls. The chelating agent will generally be present at a concentration of 0.0001% (lppm) to 5% w/w of the composition, preferably 0.05 to 2% w/w, most preferably 0.1 to 0,2% w/w, especially about 0.12% w/w. 20 The amount of buffering agent will depend on the nature of the buffering agent and the pH required for the composition. In some embodiments, the buffering agent will generally be present at a concentration of 0.0001% (1 ppm) to 5% w/w of the composition, preferably 0.01 to 2% w/w, most preferably 0.1 to 1% w/w, especially about 0.6% w/w. In other embodiments the buffering agent will be present at a concentration in the range of 0.0001 25 moles per litre to 5 moles per litre, preferably 0.001 to 2 moles per litre, most preferably 0.01 to 0.1 moles per litre, especially about 0.05 moles per litre. In one embodiment, the composition may further include an additive which enhances the antimicrobial activity of the composition. Such additives include propylene glycol, 30 glycerin, polypropylene glycol(s), polyethylene glycol(s), an antibiotic or a mixture of WO 2005/097094 PCT/AU2005/000511 - 15 propylene glycol and/or polypropylene glycol(s) and/or polyethylene glycol(s) and/or glycerin and/or an antibiotic. In another embodiment, the method of the invention includes a further subsequent step in 5 which an antibiotic is administered to the mammal. Suitable antibiotics include, but are not limited to, fluoroquinolones such as ciprofloxacin, norfloxacin, ofloxacin, enoxacin, perfloxacin, fleroxacin, enrofloxacin, marbofloxacin, sarafloxacin, orbifloxacin, danofloxacin; aminoglycosides such as streptomycin, netilmicin, kanamycin, neomycin, tobramycin, amikacin, sisomicin, ribostamycin, dibekacin, framycetin, gentamycin, 10 penicillins and aminopenicillins such as penicillin, ampicillin, amoxicillin, nafcillin, oxacillin and ticarcillin, cephalosporins such as ceftriaxone, cephalexin, cefadroxil and ceftiofur, p-lactams such as clavulanic acid which may be used in conjunction with penicillins or aminopenicillins, macrolides such as clarythromycin and erythromycin and other antibiotics such as dactinomycin, clindamycin, naladixic acid, chloramphenicol, 15 rifamopin, clofazimine, spectinomycin, polymyxin B, colistin, minocycline, vancomycin, hygromycin B or C, fusidic acid, trimethoprim and cefotaxim. Topical administration according to the invention may be by means of a liquid or vaporised composition. Suitable liquid compositions include lotions, ointments and gels 20 and include aqueous solutions. Preferred compositions are aqueous compositions. Suitable vaporised compositions include sprays and aerosols. Preferably the topical administration is administration of a liquid composition by lavage or by administration of ear drops or by spray, such as that delivered by a trigger spray bottle. Other suitable means of application are known in the art, for example, a moistened gauze, swab, cotton, foam, 25 sponge or cloth. It is particularly preferred that the liquid composition is applied by lavage. Of particular benefit is the physical flush effect that disrupts encrusted purulent and waxy accumulated material away from the ear lining, breaking it up and allowing penetration of other medications and flushing it from the ear canal. Such a liquid flushing composition may be applied using a flush applicator. Suitable carriers for use in topical 30 compositions include, but are not limited to, mineral oil, propylene glycol, polyethylene glycols, polyoxyethylene, polyoxypropylene, emulsifying wax, sorbitan monostearate, WO 2005/097094 PCT/AU2005/000511 -16 polysorbate 20, polysorbate 60, cetyl esters, wax, cetearyl alcohol, 2-octyldodecanol, benzyl alcohol, ethanol, N-methyl pyrrolidone and water. An especially preferred carrier is water. 5 As used herein, the term "effective amount" relates to an amount of the composition which, when administered according to a desired dosing regimen, provides the desired therapeutic activity or infection prevention. Dosing may occur at intervals of minutes, hours, days, weeks, months or years. An inhibiting effective amount is an amount of the composition, which when administered according to the desired dosage regimen, is sufficient to prevent 10 the multiplication of microbes responsible for infection. A therapeutic effective amount or treatment effective amount is an amount of the composition, which when administered according to a desired dosage regimen, is sufficient to at least partially attain the desired therapeutic effect, or delay the onset of, or inhibit the progression of, halt, partially or fully the onset or progression of the infection or is able to reverse or partially reverse the 15 antibiotic sensitivity of the organisms including lowering the minimum inhibitory concentration (MIC) or inducing a synergistic interaction. A preventative effective amount of the composition, which when administered according to a desired dosage regimen, is sufficient to at least partially prevent or delay the onset of the infection. 20 Suitable dosage amounts and dosing regimens can be determined by the attending physician or veterinarian and may depend on the severity of the infection as well as the general age, health and weight of the subject being treated. While in its simplest form the composition of the invention may be an aqueous 25 composition consisting of a polymeric biguanide, a chelating agent and a buffer, the composition may also include other pharmaceutically acceptable or veterinarily acceptable additives, such as carriers, diluents and excipients, anti-inflammatory agents, anti-allergic drugs and antibiotics. Suitable carriers, diluents and excipients include, where appropriate, solvents, dispersion agents, preservatives, penetration agents, surfactants, viscosity 30 adjusters, isotonic and absorption agents and the like. Some solvents, such as various WO 2005/097094 PCT/AU2005/000511 - 17 alcohols (eg. benzyl alcohol), should not be topically administered to the ear canal due to the irritant effect on a sensitive tympanum and/or canal denuded of its protective lining. In a preferred embodiment, the composition includes a non-ionic, cationic or amphoteric 5 surfactant or a combination thereof. Suitable surfactants include, but are not limited to, polysorbates, alkoxyphenol ethoxylates, poloxamines and betaines. Preferred surfactants are nonoxynol, octoxynol phospholipids, polysorbate 20, polysorbate 80 and cocamidopropyl betaine. The surfactant will generally be present at a concentration of 0.0001% w/w (lppm) to 5% w/w of the composition, preferably 0.001 to 2% w/w, most 10 preferably 0.01 to 2% w/w, especially about 0.2% w/w. In some embodiments, the preferred amount of surfactant is in the range of 0.01 to 0.02% w/w of the composition, especially about 0.015% w/w of the composition. Suitable agents that enhance penetration into exudates and waxes or through the epithelial 15 lining (epidermis and dermis) include, but are not limited to, dimethyl sulfoxide, polyvinyl pyrrolidone and light oils such as isopropyl myristate. Light oils also dissolve the oily waxes produced by ears and this is a valuable effect. Suitable anti-inflammatory agents include, but are not limited to, corticosteroids such as 20 prednisolone, triamcinolone, dexamethasone, betamethasone and momethasone, non-steroidal anti-inflammatory drugs such as, but not limited to, ibuprofen, ketoprofen, suprofen, caprofen, meloxicam, tolfenamic acid, piroxicam, firocoxib and ketorolac. Suitable anti-allergic drugs include, but not limited to, cromolyn, emedastine, olopatadine and cyclosporine. 25 Suitable viscosity enhancers include, but are not limited to, propylene glycol, polyethylene glycol, polypropylene glycol(s), bentonite, celluloses such as methylcellulose, ethylcellulose and carboxymethylcellulose, and tragacanth. 30 Suitable antibiotics include, but are not limited to, fluoroquinolones such as ciprofloxacin, norfloxacin, ofloxacin, enoxacin, perfloxacin, fleroxacin, enrofloxacin, marbofloxacin, WO 2005/097094 PCT/AU2005/000511 - 18 sarafloxacin, orbifloxacin, danofloxacin; aminoglycosides such as streptomycin, netilmicin, kanamycin, neomycin, tobramycin, amikacin, sisomicin, ribostamycin, dibekacin, framycetin, gentamycin, penicillins and aminopenicillins such as penicillin, ampicillin, amoxicillin, nafcillin, oxacillin and ticarcillin, cephalosporins such as 5 ceftriaxone, cephalexin, cefadroxil and ceftiofur, p-lactams such as clavulanic acid which may be used in conjunction with penicillins or aminopenicillins, macrolides such as clarythromycin and erythromycin and other antibiotics such as dactinomycin, clindamycin, naladixic acid, chloramphenicol, rifamopin, clofazimine, spectinomycin, polymyxin B, colistin, minocycline, vancomycin, hygromycin B or C, fusidic acid, trimethoprim and 10 cefotaxim. The composition may optionally include a preservative. Many preservatives and mixtures thereof are known to those skilled in the art. Suitable preservatives which may be incorporated in the composition include, but are not limited to, sodium benzoate, alpha 15 tocopherol, ascorbic acid, sorbic acid, benzoic acid, methyl paraben, ethyl paraben, propyl paraben, butyl paraben or sodium bisulfite. In some embodiments the preservative is methyl paraben, propyl paraben or mixtures thereof. In a preferred embodiment of the invention there is provided a method of treating or 20 preventing infections of the external ear of a dog comprising topical administration of an effective amount of an aqueous composition comprising: (i) a chelating agent, (ii) a buffering agent, and (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or 25 pharmaceutically acceptable salts thereof, to the external ear of the dog. According to a further embodiment, there is provided a use of (i) water, 30 (ii) a chelating agent, (iii) a buffering agent, and WO 2005/097094 PCT/AU2005/000511 - 19 (iv) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, in the manufacture of a medicament for the treatment of an infection in the external ear of a dog. 5 The ear canal of the modern dog is long and convoluted and is therefore not self-cleaning. Dogs are unable to keep their ears sufficiently clean to prevent infection. Dogs that are particularly susceptible to ear infection tend to have long hair and pendulous ears. 10 A further difficulty with treating ear infections in dogs is that once drops or liquid has been placed in the ear canals, it is a reflex to shake their head to remove the liquid. It is important to have an ear wash or composition that will act rapidly upon administration to the ear canal. 15 In another preferred embodiment there is provided a veterinary ear wash composition comprising: (i) water, (ii) a chelating agent, (iii) a buffering agent, and 20 (iv) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof; with the proviso that component (iv) is not chlorhexidine. Preferably the polymeric biguanide is PHMB, the chelating agent is disodium or 25 tetrasodium EDTA and the buffering agent is Tris. In yet another preferred embodiment, there is provided a veterinary ear wash composition comprising: (i) water, 30 (ii) a chelating agent, (iii) a buffering agent, WO 2005/097094 PCT/AU2005/000511 - 20 (iv) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, and (v) preservative; wherein component (iv) is present at a concentration in the range of greater than 0.02% to 5 0.5% w/w of the composition. Brief Description of the Figures Figure 1 is a graphical representation of the average reduction in Pseudomonas aeruginosa numbers (R%) for a polyhexinide/Tris/EDTA composition compared with a Tris/EDTA 10 composition at 15 and 30 seconds exposure times. Figure 2 is a graphical representation of the average reduction in Staphylococcus intermedius numbers (R%) for a polyhexinide/Tris/EDTA composition compared with a Tris/EDTA composition at 15 and 30 seconds exposure times. Figure 3 is a graphical representation of the average reduction in Malassezia 15 pachydermatis numbers (R%) for a polyhexinide/Tris/EDTA composition compared with a Tris/EDTA composition at 15 seconds exposure time. Figure 4 is a graphical representation of the in vitro antibiotic susceptibility reversion for Pseudomonas aeruginosa exposed to an ear wash formulation containing polyhexinide/Tris/EDTA composition compared with a Tris/EDTA composition. 20 Figure 5 is a graphical representation of the in vivo antibiotic susceptibility reversion for Pseudomonas aureginosa. exposed to an ear wash formulation containing polyhexinide/Tris/EDTA composition compared with a Tris/EDTA composition. Those skilled in the art will appreciate that the invention described herein is susceptible to 25 variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope. The invention will now be described with reference to the following examples which are 30 included for the purpose of illustration only and are not intended to limit the generality of the invention hereinbefore described.

WO 2005/097094 PCT/AU2005/000511 -21 Examples Composition 1 Component g/L 5 Tris 6.05 Disodium EDTA 1.20 Cosmocil CQTM 1.0 Propylene Glycol 20.0 Polysorbate 20 2.0 10 Phosphoric acid to pH 8.0 Purified water to IL Add Tris, disodium-EDTA, cosmocil CQTM, polysorbate 20 and propylene glycol to approximately 750g of purified water and stir until dissolved. Adjust to pH 8.0 with phosphoric acid. Add the balance of purified water to final mass of 1L. 15 Composition 2 Component g/L Tris 6.05 Disodium EDTA 1.20 20 CosmoCil CQTM 1.0 Polysorbate 20 2.0 Phosphoric acid to pH 8.0 Purified water to 1L Add Tris, disodium-EDTA, cosmocil CQTM, polysorbate 20 to approximately 750g of 25 purified water and stir until dissolved. Adjust to pH 8.0 with phosphoric acid. Add the balance of purified water to final mass of 1L.

WO 2005/097094 PCT/AU2005/000511 - 22 Composition 3 Component mg Tris 300 Disodium EDTA 125 5 Chlorhexidine gluconate 135 (as 20% solution) Purified water to 250g Add Tris, disodium-EDTA, chlorhexidine gluconate to approximately 200g of purified water and stir until dissolved. Add the balance of purified water to final mass of 250g. 10 Final pH of 8.7. Compositions 4-8 g/L Composition 4 Composition 5 Composition 6 Composition 7 Composition 8 Tris 6.05 - Bis-Tris -- 10.5 -- -- - BTP -- -- 14.1 -- - AMPD -- 5.3 - AMP -- -- -- -- 4.5 Disodium edetate 1.2 1.2 1.2 1.2 1.2 Hydrochloric acid to pH 6.7 to pH 7.0 to pH 6.9 to pH 6.8 to pH 6.8 (concentrated) Methyl paraben 1.0 1.0 1.0 1.0 1.0 Propyl paraben 0.3 0.3 0.3 0.3 0.3 Propylene glycol 50 50 50 50 50 Cocoamidopropyl 0.5 0.5 0.5 0.5 0.5 betaine 30% Cosmocil CQ 10 10 10 10 10 Purified water to IL to IL to IL to 1L to IL Dissolve buffering agents and disodium edetate in purified water. Adjust pH to around 15 neutral with hydrochloric acid. Dissolve parabens in propylene glycol and add to bulk. Add cocamidopropyl betaine. Add Cosmocil CQ. Add water to volume and check pH.

WO 2005/097094 PCT/AU2005/000511 - 23 Comparative Composition 1 (Purchased as Dermapet TrizEDTA) Component mg Tris 533 Disodium EDTA 141 5 trisHCl 176 Purified water to 112mL Tris, Disodium EDTA and trisHCl were mixed and ground. The ground mixture was added to a bottle and 112 mL of water added. Bottle was shaken for 10 seconds to dissolve and then left to sit for 2 hours. The pH was between 7.9 and 8.1. 10 Comparative Composition 2 (Purchased as DVM Pharmaceuticals T8 SolutionTM) Component R/L Tris 4.7 Tris HCl 4.3 15 tetrasodium EDTA 1.3 Nonoxynol 12 5.0 PPG 12 / PEG 50 5.0 Benzyl alcohol 12.0 Purified water up to 1L. 20 Tetrasodium EDTA, Tris, Tris HCI, benzyl alcohol, nonoxynol 12, and polypropylene glycol 12 (PPG 12) and polyethylene glycol 50 (PEG 50) were added stepwise to a beaker of water with stirring. The pH was adjusted to 8.5 and the volume made up to IL with water. 25 Example 1 Twelve Pseudomonas aeruginosa bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases. The isolates were selected for maximum resistance to the usual antibiotics available in clinical practice. 30 WO 2005/097094 PCT/AU2005/000511 -24 Four millilitres of two Tris EDTA formulations, Composition 1 and Comparative Composition 1, were challenged with a 1 mL inoculum containing (on average) 108 colony forming units (CFU) per mL organisms for a specific graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was 5 calculated by subculturing a specified volume onto growth media and cultured in a 37'C incubator over 24 hours. Results are expressed as %R. The R%=100(1-Ta/Cax Cb/Tb) where R = reduction in microbe numbers due to treatment. Ta = mean count in the treatment group after 10 treatment. Tb = Mean count in the treatment group before treatment. Ca = mean count in the control group after treatment. Cb = Mean count in the control group before treatment from materials and methods. The results are shown in Figure 1. Figure 1 shows a significant and rapid reduction in 15 microbe numbers when the micro-organisms are exposed to Composition 1 comprising Tris, EDTA and polyhexanide, as compared to exposure with Comparative Composition 1 which is a Tris/EDTA product. Example 2 20 Five Staphylococcus intermedius bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases. Four millilitres of two Tris EDTA formulations, Composition 1 and Comparative 25 Composition 1, were challenged with a 1mL inoculum containing (on average) 108 colony forming units (CFU) per mL organisms for a specific graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 37'C incubator over 24 hours. 30 Results are expressed as %R, as outlined in Example 1 above.

WO 2005/097094 PCT/AU2005/000511 -25 The results are shown in Figure 2. Figure 2 shows a significant and rapid reduction in microbe numbers when the micro 5 organisms are exposed to Composition 1 comprising Tris, EDTA and polyhexanide, as compared to exposure with Comparative Composition 1 which is a Tris/EDTA product. Example 3 10 A Malassezia pachydermatis yeast isolate was obtained from a commercial laboratory which receives samples from clinical cases. Four millilitres of two Tris EDTA formulations, Composition 1 and Comparative Composition 1, were challenged with a 1mL inoculum containing (on average) 105 colony 15 forming units (CFU) per mL organisms for a specific graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 37'C incubator over 48-72 hours. 20 Results are expressed as %R, as described in Example 1. The results are shown in Figure 3. Figure 3 shows a significant and rapid reduction in yeast numbers when the micro 25 organisms are exposed to Composition 1 comprising Tris, EDTA and polyhexanide, as compared to exposure with Comparative Composition 1 which is a Tris/EDTA product. Example 4 30 Organisms surviving from Example 1 above were then tested for antimicrobial susceptibility by the Kirby-Bauer Disc Diffusion Method according to the National WO 2005/097094 PCT/AU2005/000511 - 26 Committee for Clinical Standard (NCC 1990 MA-A4). The Antibiotic Sensitivity Discs: Ciprofloxacin (CIP), Amikacin (AK), Neomycin (N), Enrofloxacin (ENR), Polymyxin B (PB), Chloramphenicol (C), Gentamicin (GN), Clavulox (AMC), Ticarcillin (TIC), Framycetin (FY), Trimethoprim (SXT), and Cefotaxim (CTX). 5 The antimicrobial susceptibility test is expressed in accordance with Kirby-Bauer Disc Diffusion Method is the standardised method by the National Committee for Clinical Laboratory Standards (NCCLS, 1990, MA-A4). The % of isolates that change from resistant to a more susceptible state was expressed. 10 The results are shown in Figure 4 and indicate that there was a significant increase in micro-organism sensitivity to antibiotics after treatment with Composition 1 as compared to the sensitivity of the micro-organisms treated with Comparative Composition 1. 15 Example 5 Ten canine patients with resistant Pseudomonas otitis extema that had failed conventional treatments were either pre-treated with Composition 1 or Comparative Composition 1. Culture samples were obtained for antibiotic sensitivity testing before and after flushing 20 the ear canal with either solution. The ears were then treated again with conventional medication similar to that used in Example 4. The results are shown in Figure 5 and indicate that there was a significant increase in susceptibility of the Pseudomonas micro-organism infecting the dogs ears when they were 25 treated with Composition 1 compared to the sensitivity of the micro-organisms infecting the ears of dogs treated with Comparative Composition 1. No adverse effects or ototoxicity were observed when the dogs were treated with Composition 1.

WO 2005/097094 PCT/AU2005/000511 - 27 Example 6 Four Pseudomonas aeruginosa bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases. The isolates were 5 selected for maximum resistance to the usual antibiotics available in clinical practice. Four millilitres of three Tris EDTA formulations, Composition 4, Comparative Composition 1 and Comparative Composition 2, were challenged with a lmL inoculum containing (on average) 108 colony-forming units (CFU) per mL organisms for a specific 10 graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 37*C incubator over 24 hours. Results are expressed as %R as outlined in Example 1. 15 The results are shown in Table 1. Table 1. shows a significant and rapid reduction in microbe numbers when the micro-organisms are exposed to Composition 4, comprising Tris, EDTA and polyhexanide as compared to the Comparative Compositions which are Tris/EDTA products. 20 Table 1 Pseudomonas aeruginosa %R Composition 4 Comparative Comparative Composition 1 Composition 2 15 seconds 99.95 47.21 89.55 30 seconds 99.95 38.73 91.58 Example 7 25 Two Staphylococcus intermedius bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases.

WO 2005/097094 PCT/AU2005/000511 -28 Four millilitres of three Tris EDTA formulations, Composition 4, Comparative Composition 1 and Comparative Composition 2, were challenged with a 1mL inoculum containing (on average) 108 colony-forming units (CFU) per mL organisms for a specific 5 graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 37'C incubator over 24 hours. Results are expressed as %R, as outlined in Example 1 above. 10 The results are shown in Table 2. Table 2 shows a significant and rapid reduction in microbe numbers when the micro-organisms are exposed to Composition 4, comprising Tris, EDTA and polyhexanide as compared to exposure with Comparative Composition 1 or 2 which are Tris/EDTA products. 15 Table 2 Staphylococcus intermedius %R Composition 4 Comparative Comparative Composition 1 Composition 2 15 seconds 100.00 14.87 16.58 30 seconds 100.00 9.03 31.08 Example 8 20 Two Pseudomonas aeruginosa bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases. The isolates were selected for maximum resistance to the usual antibiotics available in clinical practice. Four millilitres of five Tris EDTA formulations, Composition 4, Composition 5, 25 Composition 6, Composition 7, and Composition 8, were challenged with a 1mL inoculum containing (on average) 108 colony-forming units (CFU) per mL organisms for a specific WO 2005/097094 PCT/AU2005/000511 - 29 graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 371C incubator over 24 hours. 5 Results are expressed as %R as outlined in Example 1. The results are shown in Table 3. Table 3 shows no difference in the reduction in microbe numbers when the micro-organisms are exposed to compositions comprising EDTA and polyhexanide and including a range of aminoalcohol or aminopolyol buffers. 10 Table 3 Pseudononas aeruginosa %R 15 seconds %R 30 seconds Composition 4 99.91 99.90 Composition 5 99.90 99.97 Composition 6 99.91 99.98 Composition 7 100.00 99.97 Composition 8 99.99 100.00 Example 9 15 Two Proteus spp. bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases. Four millilitres of three Tris EDTA formulations, Composition 4, Comparative Composition 1 and Comparative Composition 2, were challenged with a 1mL inoculum 20 containing (on average) 108 colony-forming units (CFU) per mL organisms for a specific graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 37'C incubator over 24 hours.

WO 2005/097094 PCT/AU2005/000511 - 30 Results are expressed as %R, as outlined in Example 1 above. The results are shown in Table 4. Table 4 shows a significant and rapid reduction in microbe numbers when the micro-organisms are exposed to Composition 4, comprising 5 Tris, EDTA and polyhexanide as compared to exposure with Comparative Compositions 1 or 2 which are Tris/EDTA products. Table 4 Proteus spp. %R Composition 4 Comparative Comparative Composition 1 Composition 2 15 seconds 33.41 14.12 21.39 30 seconds 46.82 20.67 16.68 10 Example 10 Two Escherichia coli bacteria isolates were obtained from University and commercial laboratories which receive samples from clinical cases. 15 Four millilitres of three Tris EDTA formulations, Composition 4, Comparative Composition 1 and Comparative Composition 2, were challenged with a 1mL inoculum containing (on average) 108 colony-forming units (CFU) per mL organisms for a specific graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) after the time treatment was calculated by subculturing a specified volume onto growth 20 media and cultured in a 37'C incubator over 24 hours. Results are expressed as %R, as outlined in Example 1 above. The results are shown in Table 5. Table 5 shows a significant and rapid reduction in 25 microbe numbers when the micro-organisms are exposed to Composition 4, comprising WO 2005/097094 PCT/AU2005/000511 - 31 Tris, EDTA and polyhexanide as compared to exposure with Comparative Compositions 1 or 2 which are Tris/EDTA products. Table 5 Escherichia coli %R Composition 4 Comparative Comparative Composition 1 Composition 2 15 seconds 100.00 19.81 34.23 30 seconds 100.00 13.90 4.83 5 Example 11 Two Malassezia pachydermatis yeast isolates where obtained from a commercial laboratory which receives samples from clinical cases. 10 Four millilitres of three Tris EDTA formulations, Composition 4, Comparative Composition 1 and Comparative Composition 2, were challenged with a lmL inoculum containing (on average) 105 colony-forming units (CFU) per mL organisms for a specific graded and varying time. The live count (by dilution in PBS Buffer with lecithin in CFU) 15 after the time treatment was calculated by subculturing a specified volume onto growth media and cultured in a 37'C incubator over 48-72 hours. Results are expressed as %R, as described in Example 1. 20 The results are shown in Table 6. Table 6 shows a significant and rapid reduction in yeast numbers when the micro-organisms are exposed to Composition 4 comprising Tris, EDTA and polyhexanide as compared to exposure with Comparative Compositions 1 or 2 which are Tris/EDTA products.

WO 2005/097094 PCT/AU2005/000511 - 32 Table 6 Malassezia pachydermatis %R Composition 4 Comparative Comparative Composition 1 Composition 2 15 seconds 99.06 37.07 0.00 30 seconds 100.00 74.58 22.78 Example 12 5 Organisms surviving from Example 6 above were then tested for antimicrobial susceptibility by the Kirby-Bauer Disc Diffusion Method according to the National Committee for Clinical Standard (NCC 1990 MA-A4). The Antibiotic Sensitivity Discs: Amikacin (AK), Neomycin (N), Enrofloxacin (ENR), Polymyxin B (PB), Gentamicin (GN), Ticarcillin (TIC), and Framycetin (FY). 10 The antimicrobial susceptibility test is expressed in accordance with Kirby-Bauer Disc Diffusion Method is the standardised method by the National Committee for Clinical Laboratory Standards (NCCLS, 1990, MA-A4). The % of isolates that change from resistant to a more susceptible state was expressed. 15 The results are shown in Table 7 and indicate that there was a significant increase in micro-organism sensitivity to antibiotics after treatment with Composition 4 comprising Tris, EDTA and polyhexanide as compared to the sensitivity of the micro-organisms treated with Comparative Compositions 1 or 2 which are Tris/EDTA products. 20 Table 7 Pseudomonas aeruginosa Composition 4 Comparative Comparative Composition 1 Composition 2 Average % reversion 23 5 14 WO 2005/097094 PCT/AU2005/000511 - 33 Example 13 A tris EDTA polyhexanide composition, as described herein, Comparative Composition 1 and Comparative Composition 2 were tested for efficacy of antimicrobial preservative 5 using BP 2003 Appendix XVI C and the results summarised in Table 8. In contrast to Comparative Compositions 1 and 2, Composition 4, the tris EDTA polyhexanide composition, meets the BP antimicrobial preservative requirements (Criteria A). Table 8 Efficacy of antimicrobial preservation Criteria of acceptance as per BP 2003 - Ear Preparations Criteria A Staphylococcus aureus Log cfu/ Ml Ear Flush Formulation Inoculum/ml of 6 hour 24 hour 28 days formulation Composition 4 6.18 pass pass pass Comparative Composition 1 7.94 pass pass pass Comparative Composition 2 7.94 pass pass pass Pseudomonas aeruginosa Log cfu/ml Ear Flush Formulation Inoculum/ml of 6 hour 24 hour 28 days formulation Composition 4 5.97 pass pass pass Comparative Composition 1 5.97 pass pass pass Comparative Composition 2 5.97 pass pass pass Candida albicans Log cfu/ml Ear Flush Formulation Inoculum/ml of 7 day 28 days formulation Composition 4 6.15 pass pass Comparative Composition 1 6.18 pass pass Comparative Composition 2 6.18 pass pass Aspergillus niger Log cfu/ml Ear Flush Formulation Inoculum/ml of 7 day 28 days formulation Composition 4 6.15 pass pass Comparative Composition 1 5.84 fail fail Comparative Composition 2 5.84 fail pass WO 2005/097094 PCT/AU2005/000511 -34 References: Ashworth C.D. and Nelson D.R., 1990, Antimicrobial potentiation of irrigation solutions containing tris-(hydroxymethyl)aminomethane-EDTA, J. Am. Vet. Med. Assoc., 197(11), 5 1513-1514. Aursnes J. 1981 a. Vestibular damage from chlorhexidine in guinea pigs. Acta Otolaryngology 92. 89-100. 10 Aursnes J. 1981 b. Cochlear damage from chlorhexidine in guinea pigs. Acta Otolaryngology 92. 259-271. Block S.S., 2001 Disinfection, Sterilization and Preservation. Chapter 2 DEFINITION of TERMS in the 5th edition published by LIPINCOTT WILLIAMS & WILKINS page 19 to 15 31. East G.C., McIntyre J.E., Shao J., 1997, Polymer, 38(15), 3973-3984 Facia A.M., Marfei G., Re. G., 1997, Potentiating effect of EDTA-Tris on the activity of 20 antibiotics against resistent bacteria associated with otitis, dermatitis and cystitis, J. Small Animal Practice, 38, 243-245. Facia A.M., Nebbia P., Re G., 1993, Potentiation of the in-vitro activity of some antimicrobial agents against selected Gram-negative bacteria by EDTA-tromethamine, 25 Veterinary Research Communication, 17, 77-84. Farng R.K., Mrha S., 2003, Antimicrobial wash and carrier solutions and uses thereof, WO 03/086332. 30 Foster A. and DeBoer D., 1998, The role of pseudomonas in canine ear disease, Compendium on Continuing Education, 20(8), 909-918.

WO 2005/097094 PCT/AU2005/000511 -35 Gotthelf N., 2003, evaluation of the in-vitro effects of tris-EDTA on the minimum inhibitory concentration (MIC) of enrofloxacin against ciprofloxacin resistant Pseudomonas aureginosa, Proceedings of the 19 th Annual Congress of ESUD/ECVD, Tenerfife, 2003, p 14 5 . 5 Green C., 1984, The clinical use of topical buffered EDTA solutions in the treatment of Gram negative bacterial infections of dogs and cats. Antimicrobial chemotherapy in 'Clinical Microbiology of Infectious Diseases of the Cat and Dog, p171, Saunders, Philadelphia. 10 Harper W.E.S. and Epis J.A., 1987, Effect of Chlorhexidine/EDTA/Tris against bacterial isolates from clinical specimens, Microbios, 51, 107-112. Harvey R.G., Harari J., Delauche A.J., 2001, Ear Diseases of the Dog and Cat, Manson 15 Publishing, page 216. Ikeda T., Yamaguchi H., Tazuke S., 1984, Antimicrobial Agents and Chemotherapy, 26(2), 139-144. 20 Izatt R.M., Pawlak K., Bradshaw J.S., 1995, Thermodynamic and Kinetic data for Macrocycle Interaction with cations, anions and neutral molecules, Chen. Rev., 95, 1261. Kirby-Bauer disc diffusion method is the standardised method by the National Committee for Clinical Laboratory Standards (NCCLS, 1990, MA-A4) in Quinn P.J., Carter, M.E. 25 Merchant S.R., 1994, Ototoxicity, Veterinary Clinics of North America: Small Animal Practice, 24(5), 976. Merchant S.R., Neer, T.M., Tedford, B.L., Twedt A.C., Cheramie P.M., Strain G.M., 1993, 30 Ototoxicity Assessment of a chlorhexidine otic preparation in dogs, Progress in Veterinary Neurology, 4(3), 72-75.

WO 2005/097094 PCT/AU2005/000511 -36 Neer T.M., 1982, Otitis media, Compendium of continuing Education, Vol4, p410- 4 17 Facia A.M., Nebbia P., Re G., 1993, Veterinary Research Communication, Vol 17, 77-84. Paterson S., 2003 New Concepts in Ear Cleaning TrizEDTA (EDTA tris) DermaPet 5 articles of Interest. Found at: http://www.dermapet.com/articles/new-concepts.html Pearman J.W., Bailey M., Harper W.E.S., 1988, Comparison of the Efficacy of "Trisdine" and Kanamycin - Colistin Bladder Instillations in Reducing Bacteriuria during Intermittent Catheterisation of Patients with Acute Spinal Cord Trauma, British J. of Urology, 62, 140 10 144. Quinn P.J., Carter M.E., Antimicrobial Agents in: Clinical Veterinary Microbiology, editors Markey B., Carter G.R., 1994, Mosby-Yearbook Europe Ltd., 95-102. 15 Rohn G.N., Meyerhoff W.L., Wright C.G., 1993, Ototoxicity of Topical Agents, Otolaryngology Clinics of North America, 26(5), 747-758. Sparkes T.A., Kemp D.T., Wooley R.E., Gibbs P.S., 1994, Antimicrobial effects of combinations of EDTA-Tris and amikacin or neomycin on the microorganism associated 20 with Otitis externa in dogs, Veterinary Research Communications, 18, 241-249. Willoughby K., 1989. Chlorhexadine and ototoxicity in cats. Veterinary Record 124 page 547. 25 Wooley R.E., Jones M.S., Gilbert J.P., Shotts E.B., 1983a, In-vitro effect of combinations of anti-microbial agents and EDTA-tromethamine on certain Gram positive bacteria, American Journal of Veterinary Research, 44(11), 2167-2169. Wooley R.E., Jones M.S., 1983b, Action of EDTA-TRIS and antimicrobial agent 30 combinations on selected pathogenic bacteria, Veterinary Microbiology, 8, 271-280.

Claims (34)

1. A method of inhibiting, treating or preventing infections of the skin in a mammal, comprising topical administration of an effective amount of a composition comprising: 5 (i) a chelating agent, (ii) a buffering agent, and (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, to the skin of the mammal. 10

2. A method according to claim 1, wherein the bis(biguanide) is a compound of formula (II): H H H H H r Xi---C-N-C-N-Z-N-C-N-C-N--X 2 NH NH NH NH (II) 15 or a tautomer thereof, wherein Z is a divalent bridging group and X 1 and X 2 are independently selected from optionally substituted alkyl, optionally substituted aryl, optionally substituted cycloalkyl, optionally substituted hertocyclyl or optionally substituted heteroaryl; or a pharmaceutically or veterinarily acceptable salt thereof. 20

3. A method according to claim 2, wherein in the compound of formula (II), X1 and X2 are both 4-chlorophenyl and Z is -(CH 2 ) 6 -.

4. A method according to claim 2, wherein in the compound of formula (II), X1 and 25 X 2 are both 3-ethylhexane and Z is -(CH 2 ) 6 -.

5. A method according to claim 1, wherein the polymeric biguanide is a compound of formula (III): WO 2005/097094 PCT/AU2005/000511 -38 X3-Z-NH-C-NH-C--Z- --- X4 NH NH or a tautomer thereof, wherein Z is absent or a divalent bridging group and each Z may be the same or different throughout the polymer; 5 n is at least 3; and X 3 and X 4 are independently selected from -NH 2 , -NH-C(=NH)-NH-CN, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclyl and optionally substituted heteroaryl; or a pharmaceutically or veterinarily acceptable salt thereof. 10

6. A method according to claim 5, wherein the polymeric biguanide is a compound of formula (IV): X 3 - (CH 2 ) 3 -(CH 2 ) 3 -NH -C-NH- H---(CH 2 ) 3 (CH 2 ) 3 - X4 NH NH 15 (IV) or a tautomer thereof, wherein n is an integer from 3 to 500 and X 3 and X 4 are independently selected from -NH 2 , -NH-C(=NH)-NH-CN, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted 20 heterocyclyl and optionally substituted heteroaryl; or a pharmaceutically acceptable salt thereof.

7. A method according to claim 6, wherein in the compound of formula (IV), n has an average value of 3 to 15. 25

8. A method according to claim 1, wherein the chelating agent is selected from aminocarboxylic acids, deferoxamine, dimercaprol, citrate, penicillamine, macrocyclic polyethers and bisphosphonates and their salts and mixtures thereof. WO 2005/097094 PCT/AU2005/000511 -39

9. A method according to claim 8, wherein the aminocarboxylic acid is selected from ethylene diamine tetraacetic acid (EDTA), nitrilotriacetic acid, nitrilotripropionic acid, diethylenetriamine pentaacetic acid, 2-hydroxyethyl-ethylenediamine-triacetic acid, 5 1,6-diamino-hexamethylene-tetraacetic acid, 1,2-diamino-cyclohexane tetraacetic acid, 0,0'-bis(2-aminoethyl)-ethyleneglycol-tetraacetic acid, 1,3-diaminopropane-tetraacetic acid, N,N-bis(2-hydroxybenzyl)ethylenediamine-NN-diacetic acid, ethylenediamine-N,N'-diacetic acid, ethylenediamine-NN'-dipropionic acid, triethylenetetraamine hexaacetic acid, 7,19,30-trioxa-1,4,10,13,16,22,27,33 10 octaazabicyclo[ 11,11,11 ]pentatriacontane (0-bis-tren), ethylenediamine-N,N' bis(methylenephosphonic acid), iminodiacetic acid, N,N-bis(2-hydroxyethyl)glycine (DHEG), 1,3-diamino-2-hydroxypropane-tetraacetic acid, 1,2-diaminopropane-tetraacetic acid, ethylenediamine-tetrakis(methylenephosphonic acid), N-(2-hydroxyethyl)iminodiacetic acid and triethylenetetramine-hexaacetic acid and salts or 15 mixed salts thereof.

10. A method according to claim 9, wherein the chelating agent is disodium EDTA, trisodium EDTA, tetrasodium EDTA, dipotassium EDTA, tripotassium EDTA, lithium EDTA, dilithium EDTA, ammonium EDTA, diammonium EDTA and calcium disodium 20 EDTA.

11. A method according to claim 10, wherein the chelating agent is disodium EDTA.

12. A method according to claim 1, wherein the buffering agent is selected from 25 amines, piperazines, morpholines, histidines, imidazoles, aminoalcohols, aminopolyols, boric acid, bicarbonate salts, sodium chloride, meglumine, phosphate buffers, citrate buffers and pharmaceutically and veterinarily acceptable salts thereof.

13. A method according to claim 12, wherein the buffering agent is selected from 30 triethylamine, triethylenetetramine, tetraethylethylenediamine, tetramethylenediamine, N,N'-diethyl-N,N'-bis(sulfopropyl)-ethylenediamine, NN'-diethylpiperazine, piperazine N,N'-bis(alkylsulfonic acids), (N-morpholino)alkylsulfonic acids, 2-aminoethanol, 2- WO 2005/097094 PCT/AU2005/000511 -40 amino-2-methyl-1-propanol, triethanolamine, tris(hydroxymethyl)aminomethane, 2-amino 2-methyl-1,3-propanediol, bis-(2-hydroxyethyl)imino-tris(hydroxymethyl)methane, 2 dimethylamino-2-methyl-1-propanol, 2-amino-2-ethyl-1,3-propanediol and 1,3-bis(tris[hydroxymethyl]methylamino)propane, N,N-bis(2-hydroxyethyl)-2 5 aminoethanesulfonic acid, N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid, N,N-Bis(2-hydroxyethyl)glycine, NN-Bis(2-hydroxyethyl)taurine, diethanolamine, triethanolamine N-tris(hydroxymethyl)methylglycine and salts thereof and mixtures thereof. 10 14. A method according to claim 13, wherein the buffering agent is tris(hydroxymethyl)aminomethane and/or salts thereof.

15. A method according to claim 1, further comprising the step of administering an antibiotic to the mammal. 15

16. A method according to claim 1, wherein the infection of the skin is caused by Staphylococcus spp., Enterobacteriacae, Klebsiella spp., Proteus spp., Pseudononads or yeasts. 20 17. A method according to claim 16, wherein the infection of the skin is caused by Staphylococcus aureus, Staphylococcus intermedius, Pseudomonas aeruginosa or Malassezia pachydermatis.

18. A method according to claim 1, wherein the method of inhibiting, treating or 25 preventing infections of the skin is a method of inhibiting, treating or preventing infections of the external ear.

19. A pharmaceutical or veterinary composition comprising: (i) a chelating agent, 30 (ii) a buffering agent, and WO 2005/097094 PCT/AU2005/000511 -41 (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof; with the proviso that component (iii) is not chlorhexidine. 5 20. A composition according to claim 19, wherein the bis(biguanide) is a compound of formula (II): XI HH H H H H_ Xi-N-C-N--C- N-Z-N-C-N-C-N- X2 NH NH NH NH (II) 10 or a tautomer thereof, wherein Z is a divalent bridging group and X1 and X 2 are independently selected from optionally substituted alkyl, optionally substituted aryl, optionally substituted cycloalkyl, optionally substituted heterocyclyl or optionally substituted heteroaryl; or a pharmaceutically or veterinarily acceptable salt thereof. 15 21. A composition according to claim 20, wherein in the compound of formula (II), X1 and X 2 are both 3-ethylhexane and Z is -(CH 2 ) 6 -.

22. A composition according to claim 19, wherein the polymeric biguanide is a compound of formula (III): 20 X3 ZNH-C-NH-C-NH Z-X4 NH C-NH(III) NH INH or a tautomer thereof, wherein Z is absent or a divalent bridging group and each Z may be the same or different throughout the polymer; 25 n is at least 3; and WO 2005/097094 PCT/AU2005/000511 - 42 X 3 and X 4 are independently selected from -NH 2 , -NH-C(=NH)-NH-CN, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclyl and optionally substituted heteroaryl; or a pharmaceutically or veterinarily acceptable salt thereof. 5

23. A composition according to claim 22, wherein the polymeric biguanide is a compound of formula (IV): X 3 -- (CH 2 ) 3 ~(CH 2 ) 3 - NH-C--NH-- C- NH- (CH 2 ) 3 (CH 2 ) 3 -X 4 NH NH 10 (IV) or a tautomer thereof, wherein n is an integer from 3 to 500 and X 3 and X 4 are independently selected from -NH 2 , -NH-C(=NH)-NH-CN, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted 15 heterocyclyl and optionally substituted heteroaryl; or a pharmaceutically acceptable salt thereof.

24. A composition according to claim 23, wherein in the compound of formula (IV), n has an average value of 3 to 15. 20

25. A composition according to claim 19, wherein the chelating agent is selected from aminocarboxylic acids, deferoxamine, dimercaprol, citrate, penicillamine, macrocyclic polyethers and bisphosphonates and their pharmaceutically and veterinarily acceptable salts. 25

26. A composition according to claim 25, wherein the aminocarboxylic acid is selected from ethylene diamine tetraacetic acid (EDTA), nitrilotriacetic acid, nitrilotripropionic acid, diethylenetriamine pentaacetic acid, 2-hydroxyethyl-ethylenediamine-triacetic acid, 1,6-diamino-hexamethylene-tetraacetic acid, 1,2-diamino-cyclohexane tetraacetic acid, 30 0,0'-bis(2-aminoethyl)-ethyleneglycol-tetraacetic acid, 1,3-diaminopropane-tetraacetic WO 2005/097094 PCT/AU2005/000511 -43 acid, N,N-bis(2-hydroxybenzyl)ethylenediamine-N,N-diacetic acid, ethylenediamine-N,N'-diacetic acid, ethylenediamine-NN'-dipropionic acid, triethylenetetraamine hexaacetic acid, 7,19,30-trioxa-1,4,10,13,16,22,27,33 octaazabicyclo[1 1,1 1,1 1]pentatriacontane (0-bis-tren), ethylenediamine-NN' 5 bis(methylenephosphonic acid), iminodiacetic acid, N,N-bis(2-hydroxyethyl)glycine (DHEG), 1,3-diamino-2-hydroxypropane-tetraacetic acid, 1,2-diaminopropane-tetraacetic acid, ethylenediamine-tetrakis(methylenephosphonic acid), N-(2-hydroxyethyl)iminodiacetic acid and triethylenetetramine-hexaacetic acid and pharmaceutically and veterinarily acceptable salts or mixed salts thereof. 10

27. A composition according to claim 26, wherein the chelating agent is disodium EDTA, trisodium EDTA, tetrasodium EDTA, dipotassium EDTA, tripotassium EDTA, lithium EDTA, dilithium EDTA, ammonium EDTA, diammonium EDTA and calcium disodium EDTA. 15

28. A composition according to claim 27, wherein the chelating agent is disodium EDTA.

29. A composition according to claim 19, wherein the buffering agent is selected from 20 amines, piperazines, morpholines, histidines, imidazoles, aminoalcohols, aminopolyols, boric acid, bicarbonate salts, sodium chloride, meglumine, phosphate buffers, citrate buffers and pharmaceutically and veterinarily acceptable salts thereof.

30. A composition according to claim 29, wherein the buffering agent is selected from 25 triethylamine, triethylenetetramine, tetraethylethylenediamine, tetramethylenediamine, N,N'-diethyl-N,N'-bis(sulfopropyl)-ethylenediamine, N,N'-diethylpiperazine, piperazine N,N'-bis(alkylsulfonic acids), (N-morpholino)alkylsulfonic acids, 2-aminoethanol, 2 amino-2-methyl-1-propanol, triethanolamine, tris(hydroxymethyl)aminomethane, 2-amino 2-methyl-1,3-propanediol, bis-(2-hydroxyethyl)imino-tris(hydroxymethyl)methane, 2 30 dimethylamino-2-methyl-1-propanol, 2-amino-2-ethyl-1,3-propanediol and 1,3-bis(tris[hydroxymethyl]methylamino)propane, N,N-bis(2-hydroxyethyl)-2 aminoethanesulfonic acid, N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid, WO 2005/097094 PCT/AU2005/000511 -44 N,N-Bis(2-hydroxyethyl)glycine, NN-Bis(2-hydroxyethyl)taurine, diethanolamine, triethanolamine N-tris(hydroxymethyl)methylglycine and pharmaceutically and veterinarily acceptable salts thereof and mixtures thereof. 5 31. A composition according to claim 30, wherein the buffering agent is tris(hydroxymethyl)aminomethane and/or pharmaceutically and veterinarily acceptable salts thereof.

32. A composition according to claim 19, further comprising pharmaceutically or 10 veterinarily acceptable carriers, diluents and/or excipients.

33. A composition according to claim 19, further comprising an additive that enhances antimicrobial activity and/or anti-inflammatory agent. 15 34. A composition according to claim 33, wherein the additive that enhances antimicrobial activity is selected from propylene glycol, glycerin, polypropylene glycol(s), polyethylene glycol(s), an antibiotic or mixtures thereof.

35. A composition according to claim 33, wherein the anti-inflammatory agent is 20 selected from corticosteroids and non-steroidal anti-inflammatory drugs.

36. A use of (i) a chelating agent, (ii) a buffering agent, and 25 (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, in the manufacture of a medicament for the treatment or prophylaxis of infections of the skin of a mammal. 30 37. A method of treating or preventing infections of the external ear of a dog comprising topical administration of an effective amount of an aqueous composition comprising: WO 2005/097094 PCT/AU2005/000511 - 45 (i) a chelating agent, (ii) a buffering agent, and (iii) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, 5 to the external ear of the dog.

38. A use of (i) water, (ii) a chelating agent, 10 (iii) a buffering agent, and (iv) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, in the manufacture of a medicament for the treatment of an infection in the external ear of a dog. 15

39. A veterinary ear wash composition comprising: (i) water, (ii) a chelating agent, (iii) a buffering agent, and 20 (iv) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof; with the proviso that component (iv) is not chlorhexidine.

40. A veterinary ear wash composition comprising: 25 (i) water, (ii) a chelating agent, (iii) a buffering agent, (iv) at least one bis(biguanide) or polymeric biguanide or a mixture thereof, or pharmaceutically acceptable salts thereof, and 30 (v) preservative; wherein component (iv) is present at a concentration in the range of greater than 0.02% ot 0.5% w/w of the composition. WO 2005/097094 PCT/AU2005/000511 - 1/5 Figure 1 Pseudomonas aeruginosa

100.00 80.00 60.00 40.00 20.00- 0.00 15 seconds 30 seconds Time exposed a Comparative Composition 1 El Composition I WO 2005/097094 PCT/AU2005/000511 - 2/5 Figure 2 Staphylococcus intermedius 100.00 80.00 60.00 40.00 0.00 15 seconds 30 seconds Time Exposed m Comparative Composition 1 EgComposition 1 WO 2005/097094 PCT/AU2005/000511 - 3/5 Figure 3 Malassezia pachydermatis 30.000 25,000 20.000 15.000 10.000 5.000 0.000 15 seconds Time Exposed FED Comparative Composition IEl Composition 1 WO 2005/097094 PCT/AU2005/000511 - 4/5 Figure 4 Pseudomonas aeruginosa 40.00% 35.00-/o 30.00% 25.00% 20.00% S15.00%/0-- - 10.00%/ -- - 5.00% - - 0.00% . Composition 1 Comparative Composition 1 Formulation WO 2005/097094 PCT/AU2005/000511 - 5/5 Figure 5 Pseudomonas aeruginosa 25.00% 20.00%" .0 15.00% 10.00% 5.00% 0.00%--J Composition 1 Comparative Composition 1 Formulation