GB2122902A - Parasiticidal formulations - Google Patents

Abstract

A parasiticidal formulation and a method for control of endo and/or ectoparasites on non-human animals comprises cypermethrin and levamisole in a suitable solvent and in which the mixture is stabilised against decomposition in storage by addition of a soluble acid. Examples of acids used are acetic and malonic acid.

Description

SPECIFICATION Parasiticidal formulations This invention relates to parasiticidal formulations which are useful in eradicating and/or controlling both endo- and ectoparasites which attack warm-blooded non-human animals.

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

In general, known 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 necessary.

Among the class of synthetic pyrethroids which are effective in controlling ectoparasites is cypermethrin (NRDC 149) whose preparation is described in UK patent No. 1,413,491. The term cypermethrin is used herein to embrace all isomers of: a-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 in our copending application No.

8205879.

One effective and preferred endoparasiticidal, and more specifically anthelmintic, compound is tetramisole (2,3,5,6-tetrahydro-6-phenylimidazo2,1-6thiazole) 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 suitable 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 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 levamisole (or 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 spoton endo- and ectoparasiticidal formulation of cypermethrin and levamisole (ortetramisole) in a suitable 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 suitable 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.

The term "parasites" is meant to include endoparasites, e.g. gut and lungworms, as well as ectoparasites, e.g. lice, keds, mites, ticks, fleas, blowfly.

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

The term "unimpaired efficacy" means that the formulations have an efficacy which is unimpaired in comparison with the efficacy of two compositions comprising the same amount of levamisole and cypermethrin separately.

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

In place of item (ii) tetramisole may be used or a 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 citric acid, acetic acid and malonic acid. The acid(s) should be selected to minimise any irritation to the animal and maximise stability.

The solvents selected for the formulations of the invention may be known insecticidal solvents.

Selection is based on the criteria: a) ability to dissolve both actives, and the 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 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 as toxicity, inflammability, unacceptable odour, high freezing point.

The solvent choice for c) and d) will depend on the target species as a solvent system with no drawbacks on cattle may not be acceptable for treatment of sheep, and vice-versa. Also it is unlikely that one single solvent will meet all the above criteria.

Among suitable solvents for selection are etheralcohols such as butyl dioxitol, monoterpenes containing hydrocarbon and ether functions such as eucalyptus oil and terpinolene, and polar oxygenated solvents such as dimethyl sulphoxide and dimethylformamide. 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(CH2CH2O)rnR wherein m = 1,2 or 3 and R = C1-C6 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 excelient spreading and absorption characteristics.

Cypermethrin will be used in most instances at between 221 10 mg/kg liveweight, depending on the species and parasite, with levamisole used at 5-1 5 mg/kg liveweight. This gives guidance on choice of active ratio and concentrations as below: Active Ratio Cypermethrin/levamisole will normally be used between the ratios 1:4 and 1:1, depending on the species and the parasite under attack.

Concentration Solubility imposes an upper limit but 10% cypermethrin/20% levamisole is a practical upper ievel, with lower levels of 2% cypermethrin/4% levamisole in particular for sheep. Concentrations lower than these are unlikely for reasons of cost and dose size.

Acid Content Solubility may again impose limits, but up to 20% incorporation is possible for malonic and citric acids, with 10% being the practical limit for acetic acid.

The following examples illustrate (1) decomposition and (2) inhibition (prevention as opposed to retardation) of decomposition.

EXAMPLE 1 A solution was made of levamisole (10% w/v) and cypermethrin (10% to w/v) in 2-(2butoxyethoxy) ethanol. After 5 months storage at ambient temperatures the solution was quantitatively analysed and found to contain the initial proportions of levamisole and cypermethrin.

After 9 months the solution was again analysed and the cypermethrin level had fallen to 2% w/v.

EXAMPLE 2 A solution was made of levamisole (10% w/v) and cypermethrin (10% w/v) in a solvent mixture of citric acid (20% w/v), acetic acid (10% w/v) and 2-(2-butoxyethoxy) ethanol (balance to 100% volume). Analysis after 5 and 9 and 12 months showed the initial proportions of levamisole and cypermethrin still remaining.

EXAMPLE 3 A mixture was made up as follows: Cypermethrin 4% Levamisole base 8% Malonic acid 20% BHT 1% Dimethylsulphoxide balance The mixture formed a clear homogenous solution, effective in controlling both ectoparasites and endoparasites on cattle, and without sign of unwanted side effects. Stability indications were satisfactory, and shelf-life expectation is high.

In formulations according to the invention, the active ratio may be 1 cypermethrin:2 levamisole.

A maximum concentration may be 10% w/v cypermethrin:20% w/v levamisole with 22% w/v:5% w/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% w/v for malonic or citric acid and up to 10% w/v acetic acid.

We have surprisingly found that (1) 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.

Claims (14)

1. A parasiticidal formulation comprising in admixture; i) Cypermethrin ii) Levamisole or tetramisole or a mixture thereof, iii) An amount of a soluble acid effective to retard or prevent decomposition of either i) or ii), and iv) A solvent.

2. A formulation according to claim 1, wherein the soluble acid is optionally substituted aliphatic carboxylic acid, either a single acid or combinations of one or more acids.

3. A formulation according to claim 2, wherein the acids have a pKa value between 0.6 to 6.0.

4. A formulation in accordance with any preceding claim, wherein the acid is citric, acetic or malonic.

5. A formulation according to claim 1 , wherein the acid has a minimal irritational 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.

6. A formulation according to any preceding claim, wherein the solvent is selected to fulfil the following: a) ability to dissolve both actives, and the 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 levamisole through the skin of the target species.

7. Formulation according to any preceding claim, wherein the solvent is selected from ether alcohols, preferably butyl dioxitol, monoterpenes containing hydrocarbon and ether functions, preferably eucalyptus oil and terpinolene, and polar oxygenated solvents, preferably dimethyl sulphoxide and dimethylformamide.

8. Formulation according to any preceding claim, wherein butylated hydroxy toluene is included in small quantities as a stabiliser and peroxide scavenger.

9. Formulation according to any preceding claim, wherein the ratio between cypermethrin and levamisole/tetramisole is between 1:4 and 1:1.

10. Formulation according to any preceding claim, wherein the concentration in solution is between 2 and 10% cypermethrin and 4 and 20% levamisole.

11. Formulation according to any preceding claim, wherein the soluble acid content is between 10 and 20%.

12. A method of controlling parasites in nonhuman 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.

13. A method in accordance with claim 12, wherein the effective dosage of the application is between 2.5 and 15 mg/Kg cypermethrin/liveweight, and between 5 and 10 mg/Kg levamisole or tetramisole/liveweight.

14. A formulation intended for the purposes herein set forth as herein described and exemplified.

1 5. A method for controlling parasites on nonhuman animals as described herein and using the formulations exemplified and described.