GB2212394A - Synergistic antibiotic composition - Google Patents

Abstract

Mixtures of tetracycline antibiotics, particularly chlortetracycline and sulpha antibacterials, particularly sulphadimidine, have synergistic effects against bacteria, especially of the Pasteurella or Bordetella species, as compared to the action of the individual ingredients alone. For sulphadimidine/chlortetracycline mixtures administered to pigs optimum weight ratios are 1:3.

Description

Synergistic antibiotic composition The present invention relates to a synergistic antibiotic composition.

Chlortetracycline and sulphadimidine are known antibiotic/antibacterials which are known to have a bacteriostatic effect against various bacteria, for example of the Pasteurella and Bordetella species. They have also been used in admixture in a weight ratio of 1:1, optionally with penicillin as a third ingredient, in the treatment of diseases of pigs, especially atrophic rhinitis, which is associated with Pasteurella multocida and Bordetella bronchiseptica. For such a purpose it has been recommended to use chlortetracycline + sulphadimidine at a rate of 110 + 110 mg/kg (ppm) or 165 + 165 mg/kg (plus 83 mg/kg penicillin) in pig food and 250 + 250 mg/kg in drinking water. However, we are not aware that any synergism between chlortetracycline and sulphadimidine has been demonstrated at this ratio and these concentrations.

We have found that other ratios of chlortetracycline and sulphadimidine give synergistic antibacterial effects against pathogenic bacteria causing disease in animals.

According to one aspect of the invention there is provided an antibacterially synergistic mixture of a tetracycline antibiotic and a sulpha antibacterial drug.

The synergistic effect of a mixture of chlortetracycline and sulphadimidine against bacteria of the Pasteurella and Bordetella species, as well as Escherichia coli, is demonstrated in the Examples below, in which the minimum inhibitory concentrations (MIC) of chlortetracycline, sulphadimidine and a 1:8 (by weight) chlortetracycline: sulphadimidine mixture against a variety of Pasteurella multocida and Bordetella bronchiseptica isolates are determined in vitro. The experimental results show that against most P. multocida isolates there is at least a four-fold reduction in the MIC for both chlortetracycline and sulphadimidine when used in the mixture as compared to its use alone, whereas in the absence of synergism only a slight reduction (not more than 2-fold at most) would be expected.

Against most B. bronchiseptica isolates there is at least a four-fold reduction in the MIC for sulphadimidine when used in the mixture as compared to its use alone.

The optimum weight ratio of the two active ingredients for synergistic effects may be determined by experiments similar to those reported in the Examples, bearing in mind that because of differing efficiencies of absorption and other factors related to bioavailability in the animal body to which the mixture is administered in vivo, the optimum in vitro ratio may need to be modified to provide the optimum in vivo ratio in the appropriate body tissue or fluid, e.g. blood serum. We estimate that absorbed sulphadimidine: chlortetracycline weight ratios should desirably be less than 20:1, preferably less than 16:1 and more preferably less than 12:1, having regard to the successful results demonstrated with an 8:1 ratio. We also think it desirable for the absorbed weight ratio to be more than 1:1, preferably more than 2:1, more preferably more than 4:1.However these ratios may be modified when using tetracycline antibiotics other than chlortetracycline and/or sulpha antibacterials other than sulphadimidine as well as when applying mixtures to combat other bacteria.

In the case of pigs, where sulphadimidine achieves a serum level approximately 24 times higher than chlortetracycline, due to differential absorption and other factors, when administered in equal amounts, the absorbed weight ratio of 8:1 sulphadimidine:chlortetracycline corresponds to an administered weight ratio of 1:3 and the other absorbed ratios to administered weight ratios of 1:1.2, 1:1.5, 1:2, 1:24, 1:12 and 1:6, so that the weight ratios for administration to pigs advantageously fall within these ranges, although the actual administration route may have some influence on the relative absorption and the ratio desirably needs appropriate adjustment for optimum effects.In the case of other domesticated or zoological animals, e.g. mammals such as horses, goats, sheep, cattle, dogs and cats, fish, crustacea and other aqúacultural species, or mankind, other relative absorption rates may apply and the administered ratio may be appropriately adjusted. Similarly, adjustments to the administered rates may be desirable for other antibiotics of either family, but in all cases the appropriate adjustment can be discovered by routine experimentation.

The tetracycline antibiotic and sulpha antibacterial may be administered in any convenient form to the animal to be treated. For example, they may be included in animal feed or drinking water, being added thereto either separately cr as a premix in an appropriate ratio. Alternatively they may be administered separately from food and drinking water in solid or liquid form, for example as an oral preparation such as a tablet or bolus, an injectable preparation, a topical preparation such as a cream or ear drops, an intrauterine or intramammary preparation or an intravaginal preparation such as a pessary. Prolonged release preparations such as those suitable for intra-ruminal release, may also be used.The invention also includes a method of producing a composition for administration to an animal and containing a tetracycline antibiotic and a sulpha antibacterial in a weight ratio producing a synergistic effect when absorbed into a body tissue or fluid of the animal comprising admixing the two antibiotics with a solid or liquid carrier or diluent. The preparations for separate administration and the premixes may contain other ingredients, for example inert ingredients such as fillers or other active ingredients such as penicillin or other antibiotics, also vitamins and minerals, all of which ingredients may be those appropriate or conventional for the administration route chosen and pharmaceutically acceptable.The two antibiotics will in general be administered simultaneously although separate but consecutive administration is not ruled out, and the invention includes a method for treating an animal curatively or prophylactically which comprises administering to the animal a tetracycline antibiotic and a sulpha antibacterial in amounts to provide in a body tissue or fluid a synergistic weight ratio of tetracycline antibiotic to sulpha antibacterial effective to combat bacteria invading the tissue or fluid. The absolute amounts of the two antibiotics administered to the animals is dependent not only on the administration route but also on the size and type of the animal.One means of gauging the absolute amount administered is to incorporate the chlortetracycline in animal food or drinking water at a concentration of 275-350 or more mg/kg, although other rates may be used such as down to 150 mg/kg or even 100 mg/kg. The sulphadimidine concentration may be adjusted according to the chlortetracycline concentration used.

Although we have referred mainly to chlortetracycline above, other tetracycline antibiotics having the basic tetracycline nucleus may be used instead of chlortetracycline, for example Tetracycline Oxytetracycline Tetracycline Hydrochloride Oxytetracycline Calciu@ Tetracycline Cyclohoxylsulphamate Oxytetracycline Dihydrate Tetracyclini Metaphosphas Oxytetracycline Hydrochloride Doxycycline Demeclocycline Doxycline Calcium Democlocycline Hydrochloride Doxycycline Dodecyclsulfamate Demeclocycline Magnesium Doxycycline Hydrochloride Rolitetracycline Doxycycline Phosphate Rolitetracycline Hydrochloride Chlortetracycline Rolitetracycline Nitrate Chlortetracycline Calcium Methacycline Chlortetracycline Hydrochloride Methacycline Hydrochloride Clomocycline Calcium Lymecycline Clomocycline Sodium Minocycline Hydrochloride Moreover, although we have referred mainly to sulphadimidine above, other sulpha antibacterials may be used instead of sulphadimidine for example sulphonamides such as Calcium Sulphaloxate Sulphaoiazine Formosulphathiazole Sulphadiazine Sodium Mafenide Acetate Sulphadimethoxyine Mafenide Hydrothloride Sulphadimidine Mafenide Propionate Sulphadimidine Sodium Noprylsulfamide Sulphacthidole Paranitrosulphathiazole Sulphafurazole Phthalysulphacetamide Acetyl Sulphafurazole Phthalysulphathiazole Sulphafurazole Diethanolamine Silver Sulphadiazine Sulphaguanidine Succinylsulphathiazole Sulphaguanole Sulfabenzamide Sulphamethizole Sulfacytine Sulphamethoxazole Sulfadoxine Sulphamethoxydiazine Sulfamerazine Sulphamethoxypyridazine Sodium Sulfamerazine Acetyl Sulphamethoxypridazine Sulfametopyrazine Sulphamoxole Sulfametrole Sulphanilamide Sulfamonomethoxine Sulphaphenazole Sulfapyrazole Sulphapyridine Sulfaquinoxaline Sulphapyridine Sodium Sulfasymazine Sulphasalazine Sulphabromomethazine Sodium Sulphasomidine Sulphacetamide Sulphathiazole Sulphacetamide Sodium Sulphathiazole Sodium Sulphachlorpyridazine Sulphathiourea With such alternative compounds the optimum synergistic ratios may vary but can be determined by routine experimentation.

The synergistic effect has been mainly discussed in terms of bacteria of the Pasteurella and Bordetella species but other species of bacteria and related microorganisms (protozoa) which may be mentioned include Bacillus Aerobacter Plasmodium Bordetella Alcaligenes Toxoplasma Brucella Coccidia Aspergillus Haemophilus Escherichia Coli Paracoccidiodes Vibrio Klebsiella Actinobacillus Yersinia Aeromonas Mycobacterium Calymmatobacterium Renibacterium Erysip@lothrix Prancisella Staphylococcus Corynebacterium Mycoplasma Streptococcus Fusobacterium Neisseria Clostridium Listeria Pastourella Flexibacter Leptospira Treponema Edwardsiella Salmonella Coxiella Norcardia Shigella Actinomyces Chlamydia Campylobacterium Plasmodium Dermatophilus Bacteroides Serratia Erysipelothrix Enterobacter Proteus Moraxella Rickettsiae Pseudomonas The invention is illustrated by the following Examples.

Examples Determination of the MIC of sulphadimidine, chlortetracycline and a sulphadimidine/chlortetracycline mixture to Pasteurella multocida and Bordetella bronchiseptica.

Source of organisms Ten cultures both of Pasteurella multocida and Bordetella bronchiseptica all of which were originally isolates from porcine respiratory material were collected from Veterinary Investigation Centres in England and subcultured onto blood agar, where they were kept at 4 C, and checked for purity and their identity confirmed by biochemical methods.

Preparation of test organisms for MIC testing Just prior to each testing a single loopful taken from each of the pure cultures was inoculated into nutrient broth No. 2 (Oxoid CM67) and incubated at 370C for 18 hours. The number of organisms grown in the broths was adjusted down to 10 - 106 per ml in sterile deionised water. A standard control E.coli (NCTC 10418) with known MICs of 64 pg of sulphadimidine (alone) and 20 pg of chlortetracycline (alone) per ml was similarly set up, and an uninoculated negative control broth was also set up.

Preparation of antibiotic solutions The sulphadimidine used in the tests had a potency of 99.72%. A correction factor of 1.0028 was therefore used when calculating the active sulphadimidine concentrations. The chlortetracyline used in the tests had a potency of 97.03%. A correction factor of 1.0306 was therefore used when calculating the active chlortetracycline concentration.

For testing purposes separate solutions containing 6400 pg/ml of active sulphadimidine or 800 pg/ml of active chlortetracycline were prepared in sterile deionised water and further sterilised by passage through a 0.45 p millipore filter system. Ten two-fold dilutions of both solutions, ranging from 1280 pg to 2.5 pg of sulphadimidine and from 16.0 pg to 0.03125 pg of chlortetracycline, per ml were prepared in sterile deionised water.

Preparation of the MIC medium Sensitised agar (Oxoid CM 409) containing 5% lysed horse blood (Oxoid SR 50) was prepared according to the manufacturer's recommendations immediately before testing.

Separate batches (18 ml) of molten (50to) medium were mixed in 90 mm diameter petri dishes with either 2 ml of each of the last nine prepared sulphadimidine dilutions or 2 ml of each of the last nine prepared chlortetracycline dilutions or both 1 ml of each of the first nine prepared sulphadimidine dilutions and 1 ml of the corresponding prepared chlortetracycline dilutions. Four replicate plates were prepared from each dilution mixture and a further four replicate plates were prepared using 2 ml of sterile deionised water, in place of 2 ml of the prepared dilutions, as growth controls. On solidification of the medium all plates were dried for 45 minutes at 37"C.

Thus 4 replicates of each of 30 plates were prepared, containing antibiotic concentrations as follows

Plate No. 1 2 3 4 5 6 7 8 9 10 pg of active sulphadimidine 64 32 16 8 4 2 1 0.5 0.25 0 per ml of medium Plate No. 11 12 13 14 15 16 17 18 19 20 pg of active chlortetra cycline per ml 8 4 2 l 0.5 0.25 0.125 0.0625 0.03125 0 of medium Plate No. 21 22 23 24 25 26 27 28 29 30 pg of active sulphadimidine 64 32 16 8 4 2 1 0,5 0,25 0 pg of active chlortetra cycline per ml 8 4 2 1 0.5 0.25 0.12 0.0625 0.03125 0 of medium Inoculation of prepared MIC plates A multipoint inoculator which dispensed approximately 0.2 lrl of one of the prepared test organisms was used to inoculate the dried MIC plates. The plates were then incubated aerobically at 37"C for 18 hours.

Reading of MIC plates The MIC plates were examined under the low-power magnification (X7) of a stereo zoom dissecting microscope.

The MIC was taken as the lowest antibiotic concentration at which no growth could be detected at the point of inoculum on all four replicate plates.

Repeated MIC assays of E.coli (NCTC 10418 - the test standard control) showed that an 8:1 weight ratio sulphadimidine:chlortetracycline consistently gave MICs of 8 pg sulphadimidine + 1 g chlortetracycline per ml.

The test results are shown in Tables 1-6 which follow, the MICs being given in the final column of each Table.

Tables 1 and 2 concern sulphadimidine used alone, Tables 3 and 4 chlortetracycline used alone and Tables 5 and 6 the sulphadimidine/chlortetracycline mixture. Tables 1, 3 and 5 concern P. multocida and Tables 2, 4 and 6 concern B. bronchiseptica. Data for E.coli appear on each Table.

Comparison of Table 5 with Tables 1 and 3 shows that, when the mixture is used, the MIC for sulphadimidine is reduced at least 4-fold for all isolates except P. multocida 1977 and is reduced 16-fold or more for six of the ten isolates and 8-fold for the E.coli standard.

The MIC for chlortetracycline is reduced at least 2-fold for all isolates except P. multocida 1977 and is reduced 4-fold or more for eight of the ten isolates and 2-fold for the E.coli standard. Only for isolate 1977 is there no synergistic improvement.

Comparison of Table 6 with Tables 2 and 4 shows that when the mixture is used, the MIC for sulphadimidine is reduced at least 2-fold for all B-bronchiseptica isolates except 1932 and 2162 and is reduced 4-fold or more for seven of the ten isolates. The MIC for chlortetracyline is held at the same level for four of the ten isolates and reduced 2-fold for two others. Only for isolates 1932 and 2162 is there no synergistic improvement.

TABLE 1 + growth M@Cs 10 R Multocida isolaies - na growth REFENFNLE RLPLICAIE SU@PHADIMIDINI CONC@@@RAIION ( g per ml ; MIC 64 32 16 8 4 2 1 0.5 0.25 0 g per ml 2013 1 + + + + + + + + + + 2 + + + + + + + + + 3 + + + + + + + + + + + + + + + + + + + + 2051 1 - - - - + + + + + + 20@ 1 @ @ @ @ @ @ @ @ @ @ 2 - - - - + + + + + + 16 3 - - - - + + + + + + 4 - - - - + + + + + + 2054 1 - - + + + + + + + + 2 - - - + + + + + + + 32 3 - - - + + + + + + + 4 - - + + + + + + + + 1952 1 - - - + + + + + + + 2 - - - + + + + + + + 16 3 - - - - + + + + + + 4 - - - + + + + + + + 1977 1 - - - - + + + + + + 2 - - - - - + + + + + 8 3 - - - - + + + + + + 4 - - - - + + + + + + 1135 1 - + + + + + + + + + 2 + + + + + + + + + + > 64 3 - + + + + + + + + + 4 - + + + + + + + + + 1136 1 - - - - - + + + + + 2 - - - - + + + + + + 8 3 - - - - - + + + + + 4 - - - - - + + + + + 1132 1 + + + + + + + + + + 2 + + + + + + + + + + > 64 3 + + + + + + + + + + 4 + + + + + + + + + + 1133 1 + + + + + + + + + + 2 + + + + + + + + + + > 64 3 + + + + + - + + + + 4 + + + + + + + + + + 2052 1 - - - - + + + + + + 2 - - - - + + + + + + 8 3 - - - - + + + + + + 4 - - - - + + + + + + STANDARD 1 - + + + + + + + + + CIONTR@L 2 - + + + + + + + + + 64 NCTC 3 - + + + + + + + + + 10-18 4 - + + + + + + + + + @@G@@@ 1 - - - - - - - - - @@@@@@ 2 - - - - - - - - - - @@ 3 - - - - - - - - - 4 - - - - - - - - - TABLE 2 + growth M@Cs 10 B. Bronchis-plica ISOLATES + no growth SU@PHADIMID@NE CONCENTRATION ( g per ml. MIC 1.EFE@E@@E R@@@@A@ @4 32 16 8 4 2 1 0.5 0.25 0 g per ml 295 1 - - - - + + + + + + 2 - - - - - + + + + + 8 3 + + + + + + + 4 - - - - - + + + + + 83 1 - - - + + + + + + + 2 - - - + + + + + + + 16 3 - - - + + + + + + + 4 - - - + + + + + + + 2161 1 1 - - + + + + + + + 2 - - - + + + + + + + 3 - - - + + + + + + + 16 4 - - - + + + + + + + 1932 1 - - - + - - - + + + 2 - - - - - - - + + + 1 3 - - - - - - - + + + 4 - - - - - - - + + + 2160 1 + + + + + + + + + + 2 + + + + + + + + + + > 64 3 + + + + + + + + + + 4 + + + + + + + + + + READING 1 - - - - + + + + + + 2 - - - - + + + + + + 8 3 - - - - + + + + + + 4 - - - - + + + + + + COMPION 1 - - - - - - - + + + 1 2 - - - - - - - + + + 1 3 - - - - - - - + + + 4 - - - - - - - + + + COMPION 1 - - - - + + + + + + 2 2 - - - - + + + + + + 8 3 - - - - + + + + + + 4 - - - - - + + + + + 2165 1 - - - - - + + + + + 2 - - - - - + + + + + 4 3 - - - - - + + + + + 4 - - - - - + + + + + 21@2 1 - - - - - - + + + + 2 - - - - - - + + + + 2 3 - - - - - - + + + + 4 - - - - - - + + + + STANDARD 1 - + + + + + + + + + CONTRO@ 2 - + + + + + + + + + 64 @@@@ 3 - + + + + + + + + + @@@@@@ 4 - + + + + + + + + + RE@@@@ 1 - - - - - - - - - CON@@@@ 2 - - - - - - - - - - @@ 3 - - - - - - - - - 4 - - - - - - - - - TABLE 3 + growth M@C's of Pasteurella multocida isolates + no growth CHLDR@@@RACYCLINC CONCENTRATION g/ml MIC REF REPLICATE 8 4 2 1 0.5 0.25 0.125 0.0625 0.03125 0 g/ml 2013 1 - - - - - + + + + + 2 - - - - - + + + + + 3 - - - - - + + + + + 0.5 4 - - - - - + + + + + 2051 1 - - - - - + + + + + 2 - - - - + + + + + + 3 - - - - - + + + + + 1.0 4 - - - - - + + + + + 2054 1 - - - - + + + + + + 2 - - - - + + + + + + 3 - - - - + + + + + + 1.0 4 - - - - - + + + + + 1952 1 - - - - + + + + + t 2 - - - - - + + + + + 3 - - - - + + + + + + 1.0 4 - - - - - + + + + + 1977 1 - - - - - + + + + + 2 - - - - - + + + + + 3 - - - - - + + + + + 0.5 4 - - - - - + + + + + 1135 1 - - - - - + + + + + 2 - - - - - t + + + t 3 - - - - - + + + + + 0.5 4 - - - - - + + + + + 1136 1 - - - - + + + + + + 2 - - - - + + + + + + 3 - - - - + + + + + + 1.0 4 - - - - + + + + + + 1132 1 - - - - + + + + + + 2 - - - - + + + + + + 3 - - - - - + + + + + 1.0 4 - - - - - + + + + + 1133 1 - - - - + + + + + + 2 - - - + + + + + + + 3 - - - - + + + + + + 2.0 4 - - - - + + + + + + 2052 1 - - - - - + + + + + 2 - - - - + + + + + + 3 - - - - + + + + + 1.0 4 - - - - + + + + + + N@@C 1 - - - + + + + + + + 10418 2 - - - + + + + + + + STANDARD 3 - - - + + + + + + + 2.0 CONTROL 4 - - - + + + + + + + NEGATI@@ 1 - - - - - - - - - CONTROL 2 - - - - - - - - - 3 - - - - - - - - - - 0 4 - - - - - - - - - TABLE 4 + growth M@C's of Bordetella bronchiseptica isolates - no growth CHLORTETRACYCLINE CONCENIRATION g/ml M@C REF REPLICATE 8 4 2 1 0.5 0.25 0.125 0.0625 0.03125 0 g/ml 295 1 - - - - - + + + + + 2 - - - - - - + + + + 3 - - - - - + + + + + 0.5 4 - - - - - + + + + + 83 1 - - - - - + + + + + 2 - - - - - + + + + + 3 - - - - - - + + + + 0.5 4 - - - - - - + + + + 2161 1 - - - - - - + + + + 2 - - - - - - - + + + 3 - - - - - - + + + + 0.25 4 - - - - - - - + + + 1932 1 - - - - - - - + + + 2 - - - - - - - - + + 3 - - - - - - - + + + 0.125 4 - - - - - - - + + + 2160 1 - - - - - - - + + + 2 - - - - - - - + + + 3 - - - - - - - + + + 0.125 4 - - - - - - - + + + READING 1 - - - - - - + + + + 2 - - - - - - + + + + 3 - - - - - - + + + + 0.25 4 - - - - - - + + + + COMPTON 1 - - - - - - - - + + 2 - - - - - - - - + + 3 - - - - - - - - + + 0.0625 4 - - - - - - - - + + compton 1 - - - - - - - + + + 2 - - - - - - - + + + 3 - - - - - - - + + + 0.125 4 - - - - - - - + + + 2165 1 - - - - - - - + + + 2 - - - - - - - + + + 3 - - - - - - - + + + 0.125 4 - - - - - - - - + + 2162 1 - - - - - - - t + + 2 - - - - - - - + + + 3 - - - - - - - + + + 0.12 4 - - - - - - - + + + STANDARD 1 - - - + + + + + + + CONTRCL 2 - - - + + + + + + + NCTC 3 - - - + + + + + + + 2.0 10418 4 - - - + + + + + + + NE@A@@@ 1 - - - - - - - - - CONIROL 2 - - - - - - - - - 3 - - - - - - - - - - 0 4 - - - - - - - - - TABLE 5 + growth M@Cs to Pasteurella multocida isolates - no growth SU@PHADIMIDINE : CONCINIRA@ION g/ml CHLURTLTRACYCLINE 64: 32: 16: 8: 4: 2: 1: 0.5: 0.25:M@C REF R@P@@@CA@ 8 4 2 1 0.5 0.25 0.125 0.0625 0.03125 0 g/ml 2013 1 - - - - - - + + + 2 - - - - - - + + + 1: 3 - - - - - - + + + 0.125 4 - - - - - - - + + + 2051 1 - - - - - + + + + 2 - - - - - + + + + 2: 3 - - - - - + + + + 0.25 4 - - - - - + + + + 2054 1 - - - - - - + + + 2 - - - - - - + + + 2: 3 - - - - - + + + + 0.25 4 - - - - - + + + + 1952 1 - - - - - - + + + 2 - - - - - - + + + 2: 3 - - - - - - + + + 0.125 4 - - - - - - + + + 1977 1 - - - + + + + + + 2 - - - + + + + + + 8: 3 - - - + + + + + + 1 4 - - - + + + + + + 1135 1 - - - - - + + + + 2 - - - - - - + + + 2: 3 - - - - - + + + + 0.25 4 - - - - - + + + + 113@ 1 - - - - - + + + + 2 - - - - - + + + + 2: 3 - - - - - + + + + 0.25 4 - - - - - - + + + 1132 1 - - - - - + + + + 2:: 2 - - - - - + + + + 0.25 3 - - - - - + + + + 4 - - - - - + + + + 1133 1 - - - - + + + + + 2 - - - - + + + + + 4: 3 - - - - + + + + + 0.5 4 - - - - + + + + + 2052 1 - - - - - + + + + 2 - - - - - - + + + 2: 3 - - - - - + + + + 0.25 4 - - - - - - + + + STANDARD 1 - - - + + + + + + CONTRO@ 2 - - - + + + + + + 8: N@T@ 3 - - - + + + + + + 1 10418 4 - - - + + + + + + NEGATINE 1 - - - - - - - - CONTRO@ 2 - - - - - - - - 3 - - - - - - - - - 0 4 - - - - - - - - TABLE 6 + growth MICs to Bordetella bron@biseptica isolates - no growth SULPHADIMIDIN@ : CON@ENTRAT@@N g/ml CHL@RTE@RACYCL@NE 64: 32: 16: 8: 4: 2: 1: 0.5: 0.25:MIC REF R@P@@CAT@ 8 4 2 1 0.5 0.25 0.125 0.0625 0.03125 0 g/ml 295 1 - - - - - - + + + + 2 - - - - - - - + + + 2: 3 - - - - - - + + + + 0.25 4 - - - - - - + + + + 83 1 - - - - - - + + + + 2 - - - - - - + + + + 2: 3 - - - - - - + + + + 0.25 4 - - - - - - + + + + 2161 1 - - - - - + + ++ + 2 - - - - - + + + + + 4: 3 - - - - - + + + + + 0.5 4 - - - - - + + + + + 1932 1 - - - - - - + + + + 2 - - - - - - + + + + 2: 3 - - - - - - + + + + 0.25 4 - - - - - - + + + + 2160 1 - - - - - - + + + + 2 - - - - - - - + + + 2: 3 - - - - - - - + + + 0.25 4 - - - - - - + + + + READING 1 - - - - - - + + + + 2 - - - - - - + + + + 2: 3 - - - - - - + + + + 0.25 4 - - - - - - + + + + COMPTON 1 - - - - - - - - + + 2 - - - - - - - - + + 0.5: 3 - - - - - - - - + + 0.0625 4 - - - - - - - - + + COMPTON 1 - - - - - - - + + + 2 - - - - - - - + + + 1: : 3 - - - - - - - + + + 0.125 4 - - - - - - - + + + 2185 1 - - - - - - - + + + 2 - - - - - - - + + + 1: 3 - - - - - - - + + + 0.125 4 - - - - - - - + + + 2162 1 - - - - - - - + + + 2 - - - - - - + + + + 2: 3 - - - - - - - + + + 0.25 4 - - - - - - - + + + STANDARD 1 - - - - - + + + + + CONTROL 2 - - - - + + + + + + 8: N@TC 3 - - - - - + + + + + 1 10418 4 - - - - - + + + + + @@GATINE 1 - - - - - - - - - CONTROL 2 - - - - - - - - - 3 - - - - - - - - - - 0 4 - - - - - - - - -

Claims (15)

1. An antibacterially synergistic mixture of a tetracycline antibiotic and a sulpha antibacterial.

2. A mixture as claimed in claim 1 in which the tetracycline antibiotic is selected from the hereinbefore given list of tetracycline antibiotics.

3. A mixture as claimed in claim 1 or 2 in which the sulpha antibacterial is selected from the hereinbefore given list of sulphonamides.

4. A mixture as claimed in claim 3 in which the tetracycline antibiotic is chlortetracycline.

5. A mixture as claimed in claim 2 in which the sulpha antibacterial is sulphadimidine.

6. A mixture as claimed in any of claims 1 to 5 which is synergistic against bacteria of the Pasteurella or Bordetella species.

7. An antibacterially synergistic mixture of chlortetracycline and sulphadimidine.

8. A mixture as claimed in claim 7 wherein the chlortetracycline and.sulphadimidine are present in a weight ratio such that on administration of the mixture to a domesticated or zoological animal the absorbed sulphadimidine:chlortetracycline weight ratio is more than 2:1 but less than 16:1.

9. A mixture as claimed in claim 8 such that the absorbed weight ratio is about 8:1.

10. A mixture as claimed in claim 7 wherein the weight ratio of sulphadimidine:chlortetracycline in the mixture is from 1:1.2 to 1:24.

11. A mixture as claimed in claim 10 wherein the weight ratio is from 1:2 to 1:6.

12. Foodstuff or drinking water for pigs, or a premix therefor, containing a mixture as claimed in any of claims 7 to 11.

13. An oral, injectable, topical, intrauterine, intramammary or intravaginal preparation for administration to pigs containing a mixture as claimed in any of claims 7 to 11.

14. A method 'of producing a composition for administration to an animal to combat bacteria of the Pasteurella or Bordetella species and containing a tetracycline antibiotic and a sulpha antibacterial in a weight ratio providing a synergistic effect against bacteria of said species when absorbed into a body tissue or fluid of the animal comprising admixing the tetracycline antibiotic and sulpha antibacterial with a solid or liquid carrier.

15. A mixture as claimed in claim 1 and substantially as hereinbefore described.