WO2008072985A2

WO2008072985A2 - Pour on formulation

Info

Publication number: WO2008072985A2
Application number: PCT/NZ2007/000360
Authority: WO
Inventors: Kathigeyan Nanjan; Fadil Al Alawi
Original assignee: Bomac Research Limited
Priority date: 2006-12-13
Filing date: 2007-12-13
Publication date: 2008-06-19
Also published as: WO2008072985A3; AU2007332222B2; BRPI0720102A2; AU2007332222A1; NZ552040A; AU2007332222C1

Abstract

The invention relates to a storage stable pour on formulation. containing one or more macrocyclic compounds with anthelmintic activity along with a glyceryl acetate solvent including triacetin. The formulation may also include other compounds with anthelmintic activity and still remain storage stable.

Description

POUR ON FORMULATION

STATEMENT OF CORRESPONDING APPLICATIONS

This application is based on the Provisional specification filed in relation to New Zealand Patent Application Number 552040, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a pour on formulation! More specifically, the invention relates to pour on formulations having one or more macrocyclic lactone compounds present and where the macrocyclic lactone compounds are storage stable. The macrocyclic lactone compound or compounds may also be mixed with other compounds having anthelmintic activity without reducing the formulation efficacy or stability.

BACKGROUND ART

Many patents exist in relation to anthelmintic formulations and combinations of these compounds.

By way of example, NZ 520295 describes a topical (pour on) formulation containing levamisole (base or phosphate; 1-30%) along with an avermectin compound (abamectin and ivermectin included) or milbemycin compound (0.01 to 5%) which is dissolved in a pyrrolidone solvent and optionally also a glycol ether based solvent.

NZ 280085 describes a liquid formulation including a macrocyclic lactone compound (includes abamectin and ivermectin; 0.1-5%) together with a vegetable oil (sesame, soya and corn oil) and a co-solvent chosen from the group comprising alcohols having 4 or more carbon atoms (benzyl alcohol, ethyl benzyl alcohol, phenethyl alcohol, and other aromatic monohydric alcohols; 1-30%).

NZ 335166 describes a pour on formulation containing triclabendazole (10-40%) dissolved in a solvent including benzyl alcohol, glycerol formal, N-methyl-2- pyrrolidone, glycol ethers and aromatic hydrocarbons. The specification teaches that the formulation may also include an additional anthelmintic compound selected from avermectins (0.25-2%); milbemycins, tetramisole and levamisole.

NZ 517227 describes a pour on for administration to sheep including an avermectin or milbemycin compounds (abamectin, ivermectin, doramectin and moxidectin; 1-4%), a solvent (benzyl alcohol, ethyl lactate and glycerol formal); a penetrating agent (propylene glycol, glycol ethers, aromatic solvents; (butyl dioxitoi)); and a spreading agent (emollient esters and dipropylene glycol monomethyl ether).

US 6,340,672 describes a formulation including a pyrrolidone solvent (N-methyl-2- pyrrolidone, 2-pyrrolidone, N,5-dimethyl-2-pyrrolidone, 3,3-dimethyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-ethoxy-2-pyrrolidone, N-ethylene-2-pyrrolidone, 1- pyrrolidone), a solvent (diethylene glycol monobutylether, benzyl benzoate, xylenes), and a parasiticidal agent (closantel, oxyclozanide, praziquantel, pyrantels, tetrahydropyrimidines, probenzimidazoles, imidazothiazoles, macrocyclic lactones, benzimadizoles, tetramisoles, avermectins, epsiprantel, morantel, febantel, netobimin, clorsulon, bunamidine, nitroscanate, melarsomine, amidines, benzoyl urea derivatives, carbamates, nitroquanidines, pyrazoles, pyrethrins, pyrethroids, pyriproxyfen, acylhydrazones). Optionally, the formulation also includes a solubility agent (caprylic acids and esters, ethyl oleate, propylene glycol, arachis oil). Optionally, the formulation also includes a stabiliser (vitamin B₁₂, vitamin E acetate, niacinamide, ascorbic acid, sodium formaldehyde sulfoxylate, butylated hydroxyaniline, thioctic acid, sorbic acid, butylated hydroxytoluene).

US 6,165,987 describes a formulation including praziquantel, an avermectin or milbemycin compound and an organic solvent (glycerol formal, ethyl lactate, benzyl alcohol and N-methyl-2-pyrrolidone). Optionally, the formulation also includes a carrier (monopropylene glycol, oil or water).

WO 00/74489 (NuFarm Ltd) describes stabilising a lipophilic compound (such as abamectin) in an organic liquid phase such as oil to form an emulsion (not a solution). The specification describes that an aqueous phase containing levamisole may then be added to the organic phase without loss in stability.

The above patent references are provided to illustrate the breadth of activity in this area and to highlight the commercial importance that incremental changes can make in such formulations. For example, the above patents all include common components but each specification use subtle changes to create different advantages.

The inventors have found that glyceryl acetate compounds offer unexpected benefits in relation to such anthelmintic formulations, particularly when using macrocyclic lactone compounds. As may be appreciated, macrocyclic lactone compounds are generally lipophilic and are more difficult to solubtlise in a therapeutically effective manner to other anthelmintic compounds. Further complicating formulation development is the further issue that whilst it is desirable to present mixtures of anthelmintic compounds, the different compounds have very different properties meaning that for example, they do not easily solubilise in the same formulation and subsequently stay storage stable without some form of ^• treatment.

Triacetin compounds (and related acetin and diacetin compounds) have been described as having transdermal and solvent properties and have the general structure:

These are compounds from the group known as glyceryl acetates.

Patents exist in relation to use of triacetin as a solvent in injectable formulations (see for example NZ 234802) and as a veterinary paste (see for example NZ 520707). NZ 306249 also describes use of triacetin in a transdermal patch.

None of these patents describe use of glyceryl acetates (and more specifically triacetin) with pour on parasiticidal formulations or, the improved stability noted by the inventors for anthelmintic compounds when dispersed into solution with glyceryl acetate solvent.

US 5,538,390 describes a combination of benzimidazole with triacetin and isopropyl acetate for use as a pour on formulation. The problem solved in US 5,538,390 is to use triacetin as a penetration enhancing agent to assist in delivery of the benzimidazole compound. What is not recognised in this patent are any improvements in stability for macrocyclic compounds nor would this be obvious in view of the quite different chemical properties between benzimidazole compounds and macrocyclic lactone compounds. It should be appreciated that it is desirable to have a pour on formulation for delivery of parasinoidal compounds that includes macrocyclic lactone compounds and optionally in combination with other anthelmintic compounds and which stabilises these compounds so that they may be stored over time with minimal physical or chemical degradation.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. DISCLOSURE OF INVENTION

The present invention is directed to pour on formulations having one or more macrocyclic lactone compounds present and which are storage stable. The formulation may also include additional compounds with anthelmintic activity. A feature of the formulations of the present invention is that they are solutions rather than being emulsions or other phase separated states. An advantage of the above solutions is that the mixture is homogeneous and is more consistent meaning that it does not crystallise, separate or settle out.

According to one aspect of the present invention there is provided a storage stable pour on veterinary formulation including at least one macrocyclic lactone compound and at least one glyceryl acetate solvent.

For the purposes of this specification, the term 'stable¹ refers to at least 3 months (preferably over 9 months) chemical stability (e.g. within ±10% w/w active compound of the stated composition) of active compound when stored at 25°C or below and at ambient humidity and of a reasonable physical stability such that the composition is substantially homogeneous and minimal separation, crystallization or turbidity in the formulation is observed.

The term 'anthelmintic' shall encompass any one or more of nematocidal, trematocidal and cestocidal active compounds.

The term 'pour on' refers to the composition being applied topically with the composition being pourable or flowing and having a fluid or liquid viscosity ranging from a free flowing liquid to a gel or paste consistency that is able to be expelled by syringe, drench or paste gun.

The inventors have surprisingly found that glyceryl acetate solvents offer unexpectedly good stability and transdermal properties over traditional solvents used in pour on formulations. In particular, the pour on is in solution due to use of these solvents rather than an emulsion or other phase separated mixture such as a ^" suspension.

The stability offered by the glyceryl acetate solvent was also unexpected over the prior art. For example, US 5,538,390 describes a combination of benzimidazole with triacetin and isopropyl acetate. The problem solved in US 5,538,390 is to improve the penetration enhancing effect due to triacetin rather than recognising the increased stability found in the present invention. It should be appreciated that benzimidazoles and macrocyclic lactones have quite different properties and different stabilities and absorption rates. As a result, it was an unexpected finding by the inventors to observe the stability noted when manufacturing the formulation of the present invention.

Preferably, the glyceryl acetate solvent is selected from: acetin, diacetin or triacetin. Most preferably, the solvent is triacetin. In preferred embodiments, the formulation includes approximately 10% to 95% w/v glyceryl acetate solvent. In a preferred embodiment, the formulation includes approximately 50% w/v glyceryl acetate. .

Preferably, the macrocyclic lactone compound or compounds are selected from: abamectin, ivermectin, eprinomectin, doramectin, and combinations thereof.

Preferably, the formulation may include at least one additional compound with anthelmintic activity selected from: closantel, oxyclozanide, praziquantel, pyrantels, tetrahydropyrimidines, probenzimidazoles, imidazothiazoles, benzimidazoles, tetramisoles, milbemycins, epsiprantel, morantel, febantel, netobimin, clorsulon, bunamidine, nitroscanate, melarsomine, and combinations thereof.

In one embodiment, the formulation includes a macrocyclic lactone compound along with a levamisole and/or a benzimidazole compound. More preferably, in the embodiment described, the formulation contains the compounds: abamectin or ivermectin in combination with levamisole and triclabendazole.

As may be appreciated, combining different anthelmintics of this nature is difficult due to the solubilities of the actives. For example, in an unaltered state, abamectin is stable at a pH between 6 and 7, more preferably pH 6.8, whereas levamisole is stable at pH 3-4. The formulation of the present invention addresses these differences by stabilising the macrocyclic lactone compound.

According to a further aspect of the present invention there is provided an anthelmintic formulation including:

(a) abamectin or ivermectin; and,

(b) levamisole or triclabendazole; and,

(c) at least one glyceryl acetate solvent.

In preferred embodiments, the formulation includes approximately 0.1-10% w/v abamectin and/or ivermectin, corresponding to a dose rate of 0.5 to 1% of compound.

Preferably, where levamisole is present, the levamisole is selected from: levamisole base, levamisole hydrochloride or levamisole phosphate, included at a rate of approximately 1 to 30% w/v.

Preferably, where triclabendazole is present, the triclabendazole is included at a rate of approximately 10 to 40% w/v.

Preferably, the glyceryl acetate solvent is selected from: acetin, diacetin, triacetin, and combinations thereof. Most preferably, the solvent is triacetin. In preferred embodiments, the formulation includes approximately 10% to 95% w/v glyceryl acetate solvent. In a preferred embodiment, the formulation includes approximately 50% w/v glyceryl acetate.

In a further embodiment, the formulation may also include at least one co-solvent characterised by dissolving the macrocyclic lactone compound(s) and not being toxic to animals. In preferred embodiments, the co-solvent used may be selected from: esters, ethers, pyrrolidones, glycols, and combinations thereof. More preferably, the co-solvent may be selected from: a pyrrolidone solvent, dipropylene glycol methyl ether, glycerol formal, ethyl lactate, and combinations thereof.

In one preferred embodiment, the co-solvent is a pyrrolidone solvent. More preferably, the pyrrolidone solvent is selected from: N-methyl-2-pyrrolidone, 2- pyrrolidone, N,5-dimethyl-2-pyrrolidone, 3,3-dimethyl-2-pyrrolidone, N-ethyl-2- pyrrolidone, N-ethoxy-2 -pyrrolidone, N-ethylene-2-pyrrolidone, 1 -pyrrolidone, and combinations thereof. Most preferably, the pyrrolidone solvent is N-methyl-2- pyrrolidone and is present at a concentration of approximately 0.5-60% w/v. Besides solvent properties, pyrrolidone can also act to aid in transdermal transfer and also provides a soothing effect. In preferred embodiments, approximately 0.5 to 60% w/v pyrrolidone is used.

In an alternative embodiment, the co-solvent is dipropylene glycol methyl ether which may be added at a rate of 0.5 to 60% w/v.

In a yet further embodiment, a mixture of both a pyrrolidone solvent and dipropylene glycol methyl ether are used together as the co-solvents.

In a further embodiment, the co-solvent is glycerol formal which may be added at a rate of 0.5 to 60% w/v.

In a further alternative embodiment, the formulation may also include at least one stabilizing antioxidant agent. Preferably, the stabilising antioxidant agent may be: butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA)₁ vitamin E, and combinations thereof.

In preferred embodiments, the stabilizing antioxidant agent is included at a rate of approximately 0.01% to 5% w/v, more preferably from 0.1 to 1 % w/v.

According to a further, aspect of the present invention there is provided a storage stable pour on veterinary formulation including an effective amount of at least one macrocyclic lactone compound and:

(a) at least one glyceryl acetate solvent;

(b) at least one co-solvent selected from: pyrrolidone solvent, dipropylene glycol methyl ether, glycerol formal, and combinations thereof; and,

(c) a stabilising anti-oxidant selected from: BHT, BHA, vitamin E, and combinations thereof.

In one embodiment, the formulation also includes other compounds with anthelmintic activity.

In further embodiments, the formulation may also include at least one further medicament selected from: vitamins, minerals, antimicrobial agent(s), antifreeze, thickening agent(s), antiflocculant(s), and combinations thereof.

According to a further aspect of the present invention there is provided a method of producing a storage stable veterinary anthelmintic composition by the steps of:

(a) dissolving at least one macrocyclic lactone compound into a co-solvent; and,

(b) adding a glyceryl acetate solvent to volume.

In selected embodiments it may be necessary to heat the co-solvent before mixing in step (a) to a temperature of approximately 40⁰C to 7O⁰C. It should be appreciated that if the active (or antioxidant if used) does not dissolve easily, then heating will be required to get a clear solution that does not crystallise upon cooling.

In selected embodiments, the mixture of step (a) may be cooled to 10-30°C before commencing step (b).

Preferably the macrocyclic lactone compound(s) added in step (a) may be selected from: abamectin, ivermectin, eprinomectin, doramectin and combinations thereof. If used, at least one benzimidazole compound may also be added at step (a). In one embodiment, the anthelmintic compounds added at step (a) are abamectin and triclabendazole.

In preferred embodiments the co-solvent may be selected from: a pyrrolidone solvent, a dipropylene glycol methyl ether, a glycerol formal, and combinations thereof.

Preferably, the glyceryl acetate solvent added at step (b) is triacetin.

In an alternative embodiment at least one stabilising antioxidant agent may also be added at step (a) or step (b).

In a further embodiment, an additional anthelmintic compound may be added to the mixture of step (a) or step (b). In one embodiment, levamisole may be added to the glyceryl acetate solvent of step (b) before the solvent is added to the mixture of step (a).

According to a further aspect of the present invention there is provided a method of treating animals for pests by administration of a formulation substantially as described above. According to a further aspect of the present invention there is provided a method of treating non-human animals for pests by administration of a formulation substantially as described above.

According to a further aspect of the present invention there is provided the use of a formulation substantially as described above in the treatment of pests in animals.

According to a further aspect of the present invention there is provided the use of a formulation substantially as described above in the treatment of pests in non- human animals.

It should be appreciated form the above description that there is provided a formulation useful for pour on veterinary administration of anthelmintic compounds including macrocyclic lactone compounds. A key advantage of the invention is the improved stability of macrocyclic lactone compounds in the formulation. A further advantage is that benzyl alcohol commonly used in many pour on preparations is not required. As noted in NZ 336139 and in the inventor's experience, benzyl alcohol formulations tend to be unstable and benzyl alcohol may be attributable to site reactions on the animal which is not acceptable, particularly in wool production.

A particular advantage of the present invention is that the formulation is well suited to stabilise macrocyclic lactone compounds including abamectin and ivermectin. The macrocyclic lactone compound(s) once incorporated into the formulation may then be administered individually or mixed with other anthelmintic compounds without risk of reducing the formulation stability.

A further advantage of the present invention is that, because the formulation is non-aqueous, it has a greater stability and avoids the need to adjust pH which can be associated with stability problems, particularly when multiple active compounds with anthelmintic activity are used. A further aspect of the present invention is that the inventors have found that pyrrolidone alone is not sufficient to stabilise the particularly sensitive macrocyclic lactone compounds such as abamectin.

The inventors have found that the formulation and composition has an unexpectedly good stability in that the compounds fully dissolve in the solvents to form a solution, and secondly the stability achieved is at least comparable to existing products.

BEST MODES FOR CARRYING OUT THE INVENTION

Examples are now provided showing various embodiments of the present invention.

EXAMPLE 1

A pour on formulation was produced as shown in Table 1.

Table 1 - Abamectin and Triclabendazole Formulation ^■

The above formulation was manufactured by:

1. Heating the co-solvent dipropylene glycol methyl ether to approximately 65°C to 70^QC;

2. Mixing stabilising antioxidant BHT and anthelmintic triclabendazole into the co-solvent;

3. Cooling the mixture of step 2 to approximately 45°C to 55⁰C and adding anthelmintic abamectin;

4. Cooling the mixture of step 3 to ambient temperature and making up to final volume with triacetin and mixing well. To test the stability, accelerated stability trials were completed using samples of formulation produced in accordance with Example 1. The samples were packed in glass bottles and stored at both ambient temperature and in a fridge and tested monthly for chemical and physical stability. Results from three stability batches were collected through to 19 months of storage.

Physically, none of the samples showed any observed physical instability such as separation, turbidity, crystal formation or other observable effect. Therefore it may be concluded that the formulation is stable.

Chemical tests were completed to ensure the active had not deteriorated. For the duration of the trial, the levels of abamectin and levamisole remained within 10% w/v of their starting levels therefore also showing that the formulation is stable chemically.

EXAMPLE 2

A pour on formulation was produced as shown in Table 2.

Table 2 - Abamectin and Levamisole Formulation

The above formulation was manufactured by producing a first solution by:

1. Heating the triacetin to approximately 6O⁰C to 65⁰C and adding stabilising antioxidant BHT and anthelmintic levamisole to the triacetin;

2. Cooling the mixture of step 1 to ambient temperature.

A second solution was produced by:

3. Heating the glycerol formal co-solvent to approximately 5O⁰C to 55⁰C and adding anthelmintic abamectin;

4. Cooling the mixture of step 3.

A final formulation was then produced by adding the mixture of step 4 to the mixture of step 2 and polysorbate 80 and adding glycerol formal to volume. Polysorbate 80 was added to act as a surfactant and penetration aid.

The above two step process was required as the anthelmintic agents used have different solubilities. In this case levamisole does not dissolve in the glycerol formal and the abamectin does not dissolve in triacetin. By pre-dissolving each agent in different solvents, the two agents can then be mixed and unexpectedly remain stable when stored.

The formulation above was stored at ambient conditions (temperature and humidity) and showed complete stability over a time period of 12 months. Measurements of stability in terms of active agent levels are indicated in Table 3 below.

Table 3 - Example 2 Formulation Measured Stability when stored at 25⁰C and 60%

EXAMPLE 3

A formulation was produced as shown in Table 4.

Table 4 -Abamectin Formulation

The above formulation was manufactured by:

1. Mixing co-solvent N-methyl-2-pyrrolidone with stabilising antioxidant BHT and anthelmintic abamectin;

2. Making up to final volume with triacetin and mixing well.

The formulation was stored at ambient conditions (temperature and humidity) and showed complete stability over a time period of 3 months.

EXAMPLE 4

A formulation was produced as shown in Table 5.

Table 5 - Ivermectin Formulation

The above formulation was manufactured by:

3. Mixing co-solvent N-methyl-2-pyrrolidone with stabilising antioxidant BHT and ivermectin;

4. Making up to final volume with triacetin and mixing well.

EXAMPLE 5

Further formulations are described below in Table 6 showing other variations in the formulation make up including use of different glyceryl acetate compounds.

Table 6 - Further Formulations

EXAMPLE 6 Further formulations are described below in Table 7 showing other variations in the formulation make up including use of different anthelmintic compounds.

Table 7 - Further Formulations

EXAMPLE 7

To confirm efficacy, animal trials were completed. The formulation of Example 1 was administered as a pour on to cattle and the resulting triclabendazole metabolites and abamectin were tested based on blood samples taken from the animals at time period of 12, 36, 6O₁ 96, 120, and 264 hours from administration.

The formulation of Example 1 was also tested against another combination abamectin and triclabendazole product commercially available under .the brand name 'Genesis Ultra™'. It is understood by the inventors that this is a benzyl alcohol based formulation corresponding to New Zealand Patent Number NZ 335166.

The results found for triclabendazole are shown in Tables 8 and 9 below.

Table 8 - Serum levels of triclabendazole sulphoxide following treatment with the Example 1 formulation or Genesis Ultra

Table 9 - Serum levels of triclabendazole sulphone following treatment with the Exam le 1 formulation or Genesis Ultra

As seen above, levels of triclabendazole over a time period of 264 hours were comparable to that found for the Genesis Ultra™ product with metabolite levels from the formulation of Example 1 being relatively similar to those found for the Genesis Ultra™ product. This result shows that the present invention provides an alternative method of stabilising at least triclabendazole with equivalent results.

As shown in Table 9 below, the levels of abamectin found following the dosing of the Example 1 formulation were not significantly different to those found following treatment with Genesis Ultra.

Table 10: Serum levels of abamectin following treatment with the Example 1 formulation or Genesis Ultra

EXAMPLE 8

The formulation of Example 2 containing abamectin and levamisole and a reference product (Eclipse™) containing the same ingredients were administered as pour-on formulations to cattle. Following these treatments, the levels of abamectin and levamisole that resulted were compared. As shown in Table 10 and Table 11 below, the levels of abamectin and levamisole were comparable to the reference product.

Table 11 - Serum levels of abamectin following treatment with the Example 2 formulation or Eclipse

Table 12: Serum levels of levamisole following treatment with the Example 2 formulation or Eclipse

The above results provide evidence that the formulation of Example 2 passes through the dermis and is absorbed into the systemic circulation.

EXAMPLE 9

The results of early trials completed by the inventors before arriving at the formulation of the present invention are shown below in Table 12.

As can be seen from the above results, the inventors have tested a variety of other formulations and not been successful. The final formulation arrived at using triacetin was unexpected and gave excellent stability results compared to earlier experiments.

It should be appreciated form the above description that there are provided formulations and compositions containing macrocyclic lactone compounds, optionally with other anthelmintic compounds, for use in pour on administration. The formulations and compositions have a number of benefits over prior art equivalents including improved stability.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT WE CLAIM IS:

1. A storage stable pour on veterinary formulation including an effective amount of at least one macrocyclic lactone compound and at least one glyceryl acetate solvent.

2. The formulation as claimed in claim 1 wherein the macrocyclic lactone compound or compounds remain within ±10% w/w of the initial macrocyclic lactone compound level over a time period of at least 3 months when stored at 25°C or below and at ambient humidity.

3. The formulation as claimed in claim 1 or claim 2 wherein the formulation remains substantially homogeneous over a time period of at least 3 months when stored at 25⁰C or below and at ambient humidity.

4. The formulation as claimed in any one of the above claims wherein the glyceryl acetate solvent is selected from: acetin, diacetin or triacetin.

5. The formulation as claimed in any one of the above claims wherein the glyceryl acetate solvent is present at a level of approximately 10% to 95% w/v.

6. The formulation as claimed in any one of the above claims wherein the macrocyclic lactone compound or compounds are selected from: abamectin, ivermectin, eprinomectin, doramectin, and combinations thereof.

7. The formulation as claimed in any one of the above claims wherein the formulation also includes an additional anthelmintic compound selected from: closantel, oxyclozanide, praziquantel, pyrantels, tetrahydropyrimidines, probenzimidazoles, imidazothiazoles, , benzimidazoles, tetramisoles, , milbemycins, epsiprantel, morantel, febantel, netobimin, clorsulon, bunamidine, nitroscanate, melarsomine, and combinations thereof.

91

8. An anthelmintic formulation in solution including:

(a) abamectin or ivermectin;

(b) levamisole or triclabendazole; and,

(c) at least one glyceryl acetate solvent.

9. The formulation as claimed in claim 8 wherein the abamectin and/or ivermectin is present at a level corresponding to a dose rate of 0.5 to 1% of agent.

10. The formulation as claimed in claim 8 or claim 9 wherein the levamisole is selected from: levamisole base, levamisole hydrochloride or levamisole phosphate, and wherein the levamisole is included at a rate of approximately 1 to 30% w/v.

11. The formulation as claimed in any one of claims 8 to 10 wherein the triclabendazole is included at a rate of approximately 10 to 40% w/v.

12. The formulation as claimed in any one of claims 8 to 11 wherein glyceryl acetate solvent is selected from: acetin, diacetin or triacetin.

13. The formulation as claimed in any one of claims 8 to 11 wherein the glyceryl acetate solvent is included at a rate of approximately 10% to 95% w/v.

14. The formulation as claimed in any one of the above claims wherein the formulation also includes at least one co-solvent selected from: esters, ethers, pyrrolidones, glycols, and combinations thereof.

15. The formulation as claimed in claim 14 wherein the co-solvent is selected from: a pyrrolidone solvent, dipropylene glycol methyl ether, glycerol formal, ethyl lactate, and combinations thereof.

16. The formulation as claimed in claim 15 wherein the pyrrolidone solvent is N- methyl-2-pyrrolidone present at a concentration of approximately 0.5 to 60% w/v.

17. The formulation as claimed in claim 15 wherein the co-solvent is dipropylene glycol methyl ether present at a rate of 0.5 to 60% w/v.

18. The formulation as claimed in claim 15 wherein the co-solvent is glycerol formal present at a rate of 0.5 to 60% w/v.

19. The formulation as claimed in any one of the above claims wherein the formulation also includes at least one stabilizing antioxidant agent.

20. The formulation as claimed in claim 19 wherein the stabilising antioxidant agent is selected from: butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), vitamin E, and combinations thereof.

21. The formulation as claimed in claim 19 or claim 20 wherein the stabilizing antioxidant agent is included at a rate of approximately 0.01% to 5% w/v,

22. A storage stable pour on veterinary formulation including an effective amount of at least one macrocyclic lactone compound and:

(a) at least one glyceryl acetate solvent;

23. A method of producing a storage stable veterinary macrocyclic lactone formulation by the steps of: (a) dissolving at least one macrocyclic lactone compound into a co-solvent; and,

(b) adding a glyceryl acetate solvent to volume.

24. The method as claimed in claim 23 wherein the co-solvent is heated before mixing in step (a) to a temperature of approximately 4O⁰C to 70⁰C.

25. The method as claimed in claim 23 or claim 24 wherein the mixture of step (a) is cooled to approximately 1O⁰C to 30⁰C before commencing step (b).

26. The method as claimed in any one of claims 23 to 25 wherein the macrocyclic lactone added in step (a) is selected from: abamectin, ivermectin, eprinomectin, doramectin and combinations thereof.

27. The method as claimed in any one of claims 23 to 26 wherein the formulation also includes triclabendazole.

28. The method as claimed in any one of claims 23 to 26 wherein the co-solvent is selected from: a pyrrolidone solvent, a dipropylene glycol methyl ether solvent, glycerol formal, and combinations thereof.

29. The method as claimed in any one of claims 23 to 27 wherein the glyceryl acetate solvent added at step (b) is triacetin.

30. The method as claimed in any one of claims 23 to 28 wherein at least one stabilising antioxidant agent may also be added at step (a) or step (b).

31. The method as claimed in any one of claims 23 to 29 wherein at least one additional anthelmintic compound may be added to the mixture of step (a) or step (b).

32. The method as claimed in any one of claims 23 to 30 wherein levamisole may be added to the glyceryl acetate solvent of step (b) before the solvent is added to the mixture of step (a).

33. A method of treating animals for pests by administration of a storage stable veterinary anthelmintic composition as claimed in any one of claims 1 to 22.

34. The use of a storage stable veterinary anthelmintic composition as claimed in any one of claims 1 to 22 in the treatment of pests in animals.