NZ204735A - Parasiticidal compositions containing cypermethrin and levamisole and/or tetramisole - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £04735 204735 Priority Date(s): .. .7.

Complete Specification Filed: Q?.'f?.$3 Class: nT APR 1986 Publication Date: ,...-> P.° Journal, No: . . /pj^Tp?.

NO QRMSI3S c h' f *28 JUNI985 ;* N.Z.No.

NEW ZEALAND Patents Act ]953 COMPLETE SPECIFICATION "Parasiticida1 formulations.

We, ROBERT YOUNG & COMPANY LIMITED, a British company of Cranstonhill Chemical Works, Elliot Street, Glasgow, G 3 8JT SCOTLAND do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - - 1 - (Followed by 1A.) 2 04/^o -i/)~ This invention relates to parasiticidal formulations uhich are useful in eradicating and/or controlling both endo- and ectoparasites uhich attack uarm-blooded non-human animals.

It is accepted that animals such as sheep and cattle can be simultaneously infested under certain conditions uith both endoparasites, including for example helminths such as gut and lunguorms and ectoparasites including for example lice, keds, mites, ticks and fleas.

In general, knoun insecticides are selective in being either endoparasiticidal or ectoparasiticidal and if it is desired to control both types of parasite then separate applications of the insecticides are usually necessar y.

Among the class of synthetic pyrethroids uhich are effective in controlling ectoparasites is cypermethrin (NRDC 149) uhose preparation is described in UK patent No. 1,413,491. The term cypermethrin is used herein to embrace all isomers of: cC - cyano -3-phenocyphenyl (-) -cis, trans -2,2- dimethyl-3-(2,2-dichlorovinyl) -cydopropanecarboxylate. The use of cypermethrin as a pour-on formulation for controlling ectoparasites and blowfly myiasis is described 204735 in Now Zealand Specification No 199904.

One effective and preferred endoparasiticidal, and more specifically anthelmintic, compound is tetramisole (2,3,5,6 - tetrahydro-fi-phenyllmidazo-2,1 -6thiazole) and its laevo isomer levamisole. Tetramisole and levamisole are described in UK patent No. 1,043,489.

It is becoming increasingly important to be able to control parasites by pour-on or spot-on formulations wherein the active compound is dissolved or suspended in a suitable solvent or carrier and poured, directly on to an infested animal, e.g. along the backline, or discrete •spots' are locally applied. There are many advantages in such applications which are well documented.

In order to reduce the number of separate insecticide applications, for economy and convenience, it is desirable to produce a parasiticidal formulation that is effective in simultaneously controlling endo- and ectoparasites. It would normally be expected that a mixture of cypermethrin and levamisole (or tetramisole) would effectively control both such species of parasite.

Indeed we have found this effect in a combination of the two compounds in a solvent. We have also however found that such a mixture begins to decompose after storage for a period of approximately 6 months storage at room temperature. Some reaction is'taking V.

•A place whereby the efficacy of the mixture is reduced as compared to the same quantity of individual ingredients.

It is therefore an object of this invention to provide a formulation of cypermethrin and leva/nisole (ox- tetramisole) that is stable for longer than 6 months by preventing or at least retarding any decomposition of the individual active ingredients.

A further object is to provide a pour-on or spot-on endo- and ectoparasiticidal formulation of cypermethrin and levamisole (or tetramisole) in a solvent and which retains useful or unimpaired efficacy against parasites after storage of the formulation for a prolonged period e.g. greater than one year.

According to one aspect of this invention there is provided a parasiticidal formulation which comprises a mixture of items (i) to (iii) below in a solvent: (i) cypermethrin, (ii) levamisole, and (iii) an amount of a soluble acid effective in retarding or preventing decomposition of either (i) or (ii).

According to a second aspect, there is provided a method of controlling parasites in non-human animals by applying to the animal a pour-on or spot-on formulation according to the first aspect. 2047 35 The term "parasites" is meant to include endo-parasites, e.g. gut and lunguorms, as ucil as ectoparasites, e.g. lice, keds, mites, ticks, fleas, bloufly.

The term "controlling parasites" is meant to include 5 the interference uith the development and/or the reproduction of said parasites.

The term "unimpaired efficacy" means that the formulations have an efficacy uhich is unimpaired in comparison uith the efficacy of two compositions comprising 10 the same amount of levamisole and cypermethrin separat&ly.

The term "useful efficacy" means that the formulations have an efficacy greater than mixture uhich has undergone decomposition but less than unimpaired efficacy.

In place of item (ii) tetramisole may be used or a 15 mixture of tetramisole and levamisole.

The preferred acids are optionally substituted aliphatic carboxylic acids, either single acids or combinations of one or more and preferably having a pKa value in the range from 0.6 to 6.0. Suitable acids are 20 citric acid, acetic acid and malonic acid. The acid(s) should be selected to minimise any irritation to the animal and maximise stability. 2 047 3 5 The solvents sc-lncteri for the formulations of the invention may be knoi'n insecticidal solvents. Selection is based on the criteria:- e) ability to dissolve both actives, and the 5 stabilising acids, b) ability to facilitate the spread of the cypermethrin across the skin surface of the target species, c) ability to facilitate penetration of the 10 levamisole through the skin of the target species, d) avoidance of significant adverse skin reactions on the target species, e) avoidance of troublesome properties such bs 15 toxicity, inflammability, unacceptable odour, high freezing point.

The solvent choice for c) and d) uill depend on the target spBcies bs b solvent system uith no drawbacks on cattle may not be acceptable for treatment of sheep, 20 and vice-vBrsa. Also it is unlikely that one single solvent uill mBet all the above criteria.

Among suitable solvents for selection are ether-alcohols such as butyl dioxitol, monoterpenes containing hydrocarbon and ether functions such as eucalyptus oil 25 and terpinolene, and polar oxygenated solvents such as dimethyl sulphoxide and dimethyIformamide. BHT (Butylated hydroxy toluene) can be included in small quantities as a stabiliser and peroxide scavenger.

As an example the ingredients can be dissolved in one or more alcohols of formula HO - (CH„-CH„-0) -R d d m wherein m - 1,2 or 3 and R - alkyl.

One suitable alcohol is 2-(2-butoxyethoxy) ethanol wherein m ■» 2 and R « ethyl. The solvent may comprise a major part of this alcohol which exhibits excellent spreading and absorbtion characteristics.

Cypermethrin will be used in moat instances at between 2^-10 mg/kg liveweight, depending on the species and parasite, with levamisole used at 5-15 mg/kg liveweight. This gives guidance on choice of active ratio and concentrations as below:-Active Ratio Cypermethrin/Levaroisole will normally be used between the weight ratios 1:4 and 1:1, depending on the species and the parasite under attack.

Concentration Solubility imposes an upper limit "but Cypermethrin/ 20Levamisole is a practical upper level, with lower levels of 2?& Cypermethrin/^ Levamisole in particular for sheep. Concentrations lower than these are unlikely for reasons of cost and dose size. 2 047 3 5 Acid Content Solubility may again impose limits, but up to ?0a' incorporation is possible for malonic and citric acids, uith 10/b being the practical limit for acetic acid.

The following examples illustrate (l) decomposition and (?) inhibition (prevention as opposed to retardation) of decomposition.

T x amplb 1 ft solution uas made of levamisole (10$ u/v) and cypermethrin (10/5 to u/v) in 2-(2-butoxyethoxy) ethanol. After 5 months storage at ambient temperatures the solution uas quantitatively analysed and found to contain the initial proportions of levamisole and cypermethrin. After 9 months the solution uas again analysed and the cypermethrin level had fallen to 2% u/v.

Example ? A solution uas made of levamisole (10?£ u/v) and cypermethrin (10% u/v) in a solvent mixture of citric acid (20^ u/v), acetic acid (10^ u/v) and ?-(2-butoxyethoxy) ethanol (balance to 100^ volume). Analysis after 5 and 9 and 12 months shoued the initial proportions of levamisole and cypermethrin still r ema ini ng. example 3 A mixture uas made up as follous:- fypermethrin Levamisole base 8^ Ma Ionic acid 20% BUT 15b Dimethylsulphoxide balance The mixture formed b clear homogenous solution, effective in controlling both ectoparasites and endoparasites on cattle, and without sign of unuanted side effects. Stability indications uere satisfactory, end shelf-life expectation is high.

In formulations according to the invention, thB active ratio may be 1 cypermethrin: 2 levamisole. A maximum concentration may be 10% u/v cypBrmethrin: 20^ u/v levamisole uith 2u/v: 5% u/v useful in controlling sheep parasites. The solvent may include oxygenated compounds such as glycols, ethers and esters. Acid proportions may be up to 20% u/v for mslonic or citric acid and up to 10% u/v acBtic acid.

Ue have surprisingly found that (l) a mixture of levamisole and cypermethrin in a solvent is liable to decompose after 6 months storage at ambient temperatures, the rate of decomposition rapidly increasing thereafter and (2) the decomposition can be inhibited or prevented to prolong the effective shelf life to practical values by adding one or more soluble aliphatic carboxylic acids. 2 Of 735

Claims (4)

1. WHAT WE CLAIM IS:- 1. A paraaiticidal formulation comprising in admixtures i) cypermethrin ii) levamisole or tetramisole or a mixture thereof, iii) an amount of 8oluble acid effective to retard or prevent decomposition of either i) or ii), and iv) a solvent.
2. 2. A formulation according to claim 1, wherein the soluble acid comprises one or more optionally substituted aliphatic carboxylic acids.
3. 3. A formulation according to claim 2, wherein the acid(s) has (have) a pKa value between 0.6 and 6.0.
4. 4. A formulation in accordance with any preceding claim, wherein the acid comprises one or more of citric, acetic or malonic acids. A formulation according to claim 1, wherein the acid has a minimal irrltational effect on the skin of an animal for which the formulation is intended to be used, and a maximal effect of stabilisation of the formulation. -10- 6. Forimilation according to any preceding olairo, wherein the solvent is selected from ether alcohols, monoterpenes containing hydrocarbon and ether functions, and polar oxygenated solvents. 7. Formulation according to any preceding claim, wherein the weight ratio between cypermethrin and levamisole/tetramisole is between 1:4 and 1:1, 8. Formulation according to any preceding claim, wherein the ooncentration in solution is between 2 and 105» v/v cypermethrin and 4 and 20ft w/v levamisole, 9. Formulation according to any preceding claim, wherein the soluble acid content is between 10 and 20fi> w/v 10. A method of controlling ectoparasites in non-human 204735 -11- animals by applying to the skin or fleece of the animal by a pour-on or spot-on method a formulation according to any one of the preceding claims. 11. A method in accordance with claim 10, wherein the effective dosage of the application is between 2.5 and 15 mg/Vg cypermethrin/liveweight, and between 5 and 10 mg/kg levamisole or tetramisole/liveweight. 12. A parasiticidal formulation as claimed in claim 1 substantially as herein described and exemplified in example 2 or 15. A method for controlling parasites on non-human animals as claimed in claim 10 substantially as described herein. ROBERT YOUNG & COMPANY LIMITED By their attorneys HENRY HUGHES LIMITED