AU2005201107B2 - Anthelmintic compositions - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION Invention Title: ANTHELMINTIC COMPOSITIONS The following statement is a full description of this invention, including the best method of performing it known to me: ANTIHELMINTIC COMPOSITION FIELD OF THE INVENTION This invention relates to novel anthelmintic formulations and in particular it relates to stable veterinary formulations containing the anthelmintic triclabendazole.

BACKGROUND

In general for ease of application to large numbers of animals, farmers and veterinary surgeons prefer to treat farm animals with pour-ons rather than oral drenches or injectables. Pour-ons are typically relatively thick liquids applied in small doses to the neck or back line of the animal. In the case of sheep pour on, the applicator guns are adapted to supply a dose of about 5ml to 10ml, and in the case of cattle the dose (depending upon the product) is typically about 40ml to about 60ml. Most pour ons have the active in solution, and the solvent or solvent system is chosen to allow the active to pass through the dermal layer and provide a sufficiently high systemic amount of the active quickly enough. The solvent system needs to be non-irritant to the farmer and the animal, stable, non-toxic, non-carcinogenic, and capable of being used in a pour-on applicator gun. Because of the small volume of each dose (too much would result in liquid running off the animal's back) the pour on formulation is typically designed so that sufficient active is contained within the solvent system that a typical designed dose rate of lml of pour on for each 10kg of animal live weight is the standard. Thus a 10ml dose of a pour on would supply sufficient active to treat a 100kg sheep.

Parasitologists on the other hand recommend the use of oral drenches as there is usually a better take up of active from an oral drench than a pour on.

Fonnulators prefer to design solutions rather than suspensions for veterinary purposes, as solutions can normally be used for either the pour on route of administration or the oral route of administration, and solutions are usually far more stable than suspensions when stored in bulk. But if the active is known to be sparingly soluble in water or most practical solvents then the formulalor will favour a suspension for use as an oral drench.

It is particularly advantageous to provide liquid formulations which contain a sufficient quantity of an active anthelnintic agent in a solution which can be easily administered by way of a pour-on.

The benzimidazole class of active agents are known for their anthelmintic activity.

They are known to be sparingly soluble and are either made up in tablet or powder form (for use with small animals) or typically made up as suspensions for use in oral drenches.

Of all the benzimidazole's known, triclabendazole, which is a halogenated benzimidazole, is highly effective against liver flukes (fasciolosis) at all stages of their life cycle. Triclabendazole is known as 5-Chloro-6-(3,3-dichlorophenoxy)-2methylthio-lH-benzimidazole, and is represented by the structural Formula 1.

Cl 0 N Y

SCHS

Other active agents within the benzimidazole class of actives such as Albendazole are only effective against adult fluke.

Diseases caused by parasitic helminths such as nematodes, cestodes and trematodes (liver fluke) can cause severe economic losses in ruminants and other animals. It has been estimated that 40 million sheep and 6 million cattle graze on pastures contaminated with fasciola hepatica (liver fluke).

Ruminants, such as sheep, cattle and goats, are susceptible to fasciola, the disease caused by parasitic liver flukes and it is of critical importance that formulations effective against the disease are available.

Fasciola hepatica infection is widespread and is generally associated with low lying wet or water-covered areas. Areas where the average annual rainfall is at or above about 600mm and irrigation areas in particular, tend to create ideal living/propagating environments for aquatic snails which serve as intermediate hosts for first larvae of fasciola hepatica (miracidia). The miracidia develop and multiply and eventually leave the snail host and encyst on vegetation forming metacercarial (infective stage of fasciola hepatica). When the vegetation is consumed by a grazing animal the metacercarial excyst in the small intestine. The metacercarial eventually releases immature flukes that penetrate the intestinal wall into the abdominal cavity. Acute infections can result from the immature flukes burrowing through the liver substance.

Death often follows as a result of concomitant blood loss.

It has been difficult to provide liquid formulations containing triclabendazole in solution due to the highly insoluble nature of the compound. This has resulted in anthelmintic formulations containing triclabendazole or a pharmaceutically acceptable salt thereof being prepared as suspensions for oral administration.

Commercial drench formulations of triclabendazole are known in which triclabendazole is suspended in a liquid carrier. Such formulations are administered orally via an appropriate drenching apparatus or by subcutaneous injection. Oral triclabendazole suspension formulations are commercially available and marketed under the trade name 'Fasinex' 120 or 240. Such formulations can have a triclabendazole concentration in the order of 120g/l (or240g/l), which equates to 12% w/v (24% A 50 ml (25ml) dose of Fasinex 120 (240) equates to a dose of 6g triclabendazole/500kg beast (12mg/kg).

While oral (drench) suspension formulations containing triclabendazole have been available and successful in treating fasciolosis, the method of administering a suitable volume of oral formulation often requires a suitably experienced/qualified person to administer a dose. Dosing a herd of animals can therefore be laborious, time consuming and place a severe economic strain on a conventional farm, Treatment of fasciolosis by way of a single injection represents an even less practical option for a farmer. Pour-on formulations containing a benzimidazole compound are therefore desirable within the farming community.

To date only one benzimidazole pour-on formulation has reached the market and it is based on a suspension, which is not particularly effective. In W095/23590 (Bomac), a pour-on formulation is described in which a benzimidazole, selected from Oxfendazole and/or Albendazole, is formulated in a suspension. Suspensions of albendazole in accordance with formulations described in 'Bomac' have not been effective in the treatment of a parasitic burden. In any case as stated earlier albendazole is not the preferred active for treatment of liver fluke.

Other pour-on formulations have been suggested in patent literature in which an active agent is dissolved; emulsified; or suspended in a solvent/solvent mixture.

Anthelmintic formulations are known which contain oxfendazole; tetramisole and levamisole that exhibit anthelmintic action as a pour-on comparable to that of analogous oral or injectable treatments. French patent registration no. 96 14068 teaches a formulation for topical administration including oxfendazole in an amount of 5% w/v dissolved in a non-aqueous 'vehicle', a non-aqueous co-solvent, a nonionic surfactant and a polymer. As stated earlier however such anthelmintics are not effective in the treatment of early immature and immature fasciola hepatica.

Benzimidazoles in general and triclabendazole in particularly are insoluble in water.

Benzimidazoles and in particular triclabendazole have only been supplied in a suspension formulation for dosing by oral administration. Suspensions are less able to be absorbed when applied by way of a pour-on.

Pour-ons must be formulated to penetrate the animal's dermis which is the body's natural barrier. While a suspension may be absorbed from the digestive tract the same formulation applied to the skin would be less able to be absorbed.

Pour-on formulations have been used to deliver easily soluble actives such as synthetic pyrethroids and active agents in the class of 'avermectins' one such product containing the active ivermectin is marketed under the trade name 'Ivomec pour-on'.

With most of the actives applied as pour-ons to the dermis, the dose rate at which it is applied is increased when compared to an oral or injectable formulation. This is to offset less efficient absorption through skin tissues.

The solubility characteristic of triclabendazole makes formulating an effective triclabendazole pour-on extremely difficult. A number of rate limiting barriers are faced in formulating active ingredient(s) in a commercially effective dosage form including efficient and sufficient absorption to provide systemic amounts of active quickly; (ii) minimal exposure of an animal to a toxic dosage form; and (iii) stability of formulation.

These and other limitations are amplified given the characteristics of triclabendazole and the desire to provide a triclabendazole pour-on formulation, which is additionally required to permeate across an animals dermis, and be sufficiently absorbed and transported to the site of infection (liver). Even further barriers exist to the extent that a sufficient kill rate of liver fluke needs to be achieved to substantially minimise potential development of drug resistant parasitic strains.

While reference has been made to prior art in the specification it is not to be taken as an admission that art forms part of the common general knowledge.

OBJECT

One objcct of the invention is therefore to obviate at least one of the disadvantages of the prior art. It is a further object of the invention to provide an improved stable liquid anthelmintic solution containing an effective amount of TCBZ which is suitable for administration to warm blooded animals or one which at least provides the public with a useful choice.

STATEMENT OF INVENTION In one aspect the invention provides a pour-on veterinary anthelmintic formulation containing one or more anthelmintic actives wherein the anthelmintic active or one of the anthelmintic actives is triclabendazole or a pharmaceutically acceptable salt thereof and the triclabendazole is in a stable liquid solution, and wherein The solution contains at least 20% w/v of triclabendazole and a solvent system containing one or more of solvents selected from the group consisting of benzyl alcohol, glycerol formal, n-methyl-2-pyrrolidone, and glycol ethers.

The present invention provides a liquid formulation which solubilises TCBZ in high concentrations that can be easily administered by way of a pour-on.

The solvent system of the present invention can contain at least one of benzyl alcohol and glycerol formal. The solvent system can contain at least two or more of the solvents selected from the group consisting of benzyl alcohol, glycerol formal, nmethyl-2-pyrrolidone, and glycol ethers, The majority solvent in the solvent system can be a glycol ether. Preferably the glycol ether can be butyl dioxitol. The solvent system can include benzyl alcohol as a second solvent.

The triclabendazole in the pour-on formulation can be present in the range 20-40% w/v. The pour-on veterinary formulation can include at least one additional anthelmintic selected from the group of avermectins, milbemycins, tetramisole and levamisole, and which is soluble in the solvent system as previously claimed. The additional anthelmintic is an avermectin. The avermectin can be present in the range 0.25 to 2% w/v.

In a related aspect of the present invention there is provided a method of treating warm blooded animals for parasites by administering to the animal a pour-on formulation containing one or more anthelmintic actives wherein the anthelmintic active or one of the anthelmintic actives is triclabendazole or a pharmaceutically acceptable salt thereof and the triclabendazole is in a stable liquid solution, and wherein the solution contains at least 20% w/v of triclabendazole and a solvent system containing one or more of solvents selected from the group consisting of benzyl alcohol, glycerol formal, n-methyl-2-pyrrolidone, and glycol ethers.

In a further related aspect there is described a method of treating liver flukes in warm blooded animals by administration of a pour-on formulation containing one or more anthelmintic actives wherein the anthelmintic active or one of the anthelmintic actives is triclabendazole or a pharmaceutically acceptable salt thereof and the triclabendazole is in a stable liquid solution, and wherein the solution contains at least w/v of triclabendazole and a solvent system containing one or more of solvents selected from the group consisting of benzyl alcohol, glycerol formal, n-methyl-2pyrrolidone, and glycol ethers.

There is further disclosed a pour-on formulation for treatment of fasciolosis in warm blooded animals including: a solution of triclabendazole or a pharmaceutically acceptable salt thereof substantially dissolved in a solvent system of at least one solvent selected from the group benzyl alcohol, glycerol formal, n-methyl-2-pyrollidone, glycol ethers and aromatic hydrocarbons, the triclabendazole being present in an amount equal to or greater than The solvent system can include a major proportion of a glycol ether and a minor proportion of an alkyl or aromatic alcohol.

The pour-on formulation of the present invention is effective in treating ruminants with the disease fasciolosis. The present invention provides a pour-on formulation in which at least 20% w/v triclabendazole or a pharmaceutically acceptable salt thereof is available for permeation of the dermal layer and subsequent absorption.

The pour-on formulation can be administered in an amount of up to about 50ml by the dosing means. The solvent system of the present invention is able to solubilise a sufficiently high amount of triclabendazole such that the formulation can be administered from a conventional pour-on dosing gun substantially reducing the need for multiple dosing.

The solvent system can further include a solubilisation agent selected from polyethylene glycols (PEG's) class of compounds. The solvent system can further include a solvent selected from glycerol formal and n-methyl-2-pyrrolidone. The PEG compound can be PEG 400 and can be present in an amount of about 14.5% w/v.

The glycol ether can be butyl dioxitol and the aromatic alcohol can be benzyl alcohol wherein butyl dioxitol and benzyl alcohol are present in amount ranging between about 40% w/v to 60% w/v and about 5% w/v to 15% w/v respectively.

The triclabendazole can be present in an amount of greater than or equal to 30% w/v.

In an embodiment of the present invention there is described a pour-on formulation for treatment of parasitic diseases including fasciolosis in warm blooded animals including: a solution of triclabendazole or a pharmaceutically acceptable salt thereof substantially dissolved in a solvent system, the triclabendazole being present in an amount of about abamectin in an amount of about 0.5% w/v; wherein the solvent system includes butyl dioxitol; benzyl alcohol; and PEG 400 in an amount of about 50% w/v; 5% w/v; and 14.5% w/v respectively.

In a further related aspect of the present invention there is described a method of treatment of fasciolosis in warm blooded animals including: providing a pour-on formulation having: a solution of triclabendazole or a pharmaceutically acceptable salt thereof substantially dissolved in a solvent system, the triclabendazole being present in an amount equal to or greater than 20%w/v; and a solvent system including a major proportion of a glycol ether and a minor proportion of an alkyl or aromatic alcohol; applying a quantity of up to about 50ml of the pour-on formulation on to a skin surface of the warm blooded animal.

One advantage of the present invention is that TCBZ is provided in a pour-on solution in high concentrations. The high concentration of TCBZ in the pour-on solution allows a farmer to administer manageable doses directly onto an animal's hide. This substantially obviates the need for oral dosing. A further advantage is that the solvent system of the invention aids permeation of TCBZ across an animal's dermal layer and subsequent absorption into the bloodstream for efficient transport to the diseased site.

Generally suspension pour-on formulations have suffered from insufficient/inefficient permeation across an animal's dermal layer. Consequently the amount of an active agent in a suspension form which is available for absorption is extremely low and can expose an animal to sub-optimal therapeutic drug concentrations. This is clearly undesirable since drug resistant strains of a parasite may develop. For this reason there is a general aversion within the parasitology community to adopt a pour-on dosage form.

The concept of increasing the drug loading of a single active formulation is generally not a preferred approach by conventional parasitology as a method of combating drug resistance and offsetting poor dermal absorption characteristics. Indeed increasing drug loading in a pour-on formulation to offset exposure to sub-optimal drug concentration is viewed counter to current attempts to overcome increasing development of drug resistant parasitic strains. Parasitologists in contradistinction have attempted to address developing resistance by trialling combinations of active agents in attempts to find a synergistic combination.

PREFERRED EMBODIMENTS It has now been found that stable liquid formulations containing the active triclabendazole in solution can be prepared and that these actives can be absorbed through the skin to control the infection of liver in animals in particular cattle.

The above, and other aspects of the invention, which should be considered in all its novel aspects will be apparent from the following examples.

EXAMPLE 1 The formulation of this example is shown in table 1. It is suitable for administration as a pour-on, in particular to cattle. The recommended dose rate is: Table 1 INGREDIENT G/100mL Abamectin Triclabendazole 30.0 Butyl dioxitol 50.0 Benzyl Alcohol PEG 400 to volume To prepare the formulation add the abamectin and benzyl alcohol. To this add butyl dioxitol and the triclabendazole. Warm to40 C and stir to dissolve. Cool mix to less C and dilute to volume with PEG 400. It will be apparent to the skilled addressee if filtering is necessary at this point.

TRIALS

Stability Trials A stability trial was conducted to ensure that the triclabendazole solution was stable.

A formulation made as described in example I ("Formulation was stored at ambient for 11 months. At the conclusion of the storage period samples were tested for total abamectin and triclabendazolelevels. The results are presented in table 2 below.

Table 2: Stability Trial Formulation 1 Abamectin Abamectin Total Triclabendazole BI, Bib Abamectin Date of 0.48 0.02 0.50 31.3 manufacture Dayl End of trial 0.48 0.008 0.49 28.9 Day 345 The results clearly show that the triclabendazole remained in solution. There was no loss in activity for either abamectin or triclabendazole.

Efficacy Trials Trials were conducted comparing the efficacy of the Formulation 1 with two other treatments and a control. The trial included twenty animals all confirmed infected with Fasciola spp. The animals were divided into four groups of five animals. The animals were ranked on the basis of faecal fluke egg counts, and divided into blocks of four. Animals from each block were randomly allocated to one of the four treatment groups. Egg counts were performed twice on animals a week prior to the trial to confirm all animals had a Fasciola spp burden. At day zero of the trial all animals were treated according to the protocol set out in Table 3. Groupl animals were left untreated as controls. Group 2 received Formulation 1. Group 3 were the positive control group and received a commercial flukacide Fasinex 50 (Novartis).

Group 4 received triclabendazole oral formulations at levels shown in table 3.

During the course of the trial all animals were grazed as a single group grazing on fluke infested pastures up to treatment and then removed to fluke free pastures post treatment.

Table 3 Group 1 No treatment Group 2 At 5ml per 50 kg topically with the pour-on of Formulation 1 Group 3 At 12ml per 50 kg orally with Fasinex 50 50mg per ml of triclabendazole Group 4 At 12ml per 50 kg orally with the triclabendazole oral drench containing 50 mg per ml of triclabendazole At 14 days post treatment all animals were sacrificed. Total worm counts were performed using the following procedures: 1. Faecal egg counts 2. Fasciola hepatica liver counts. The liver counts were performed by collecting the entire liver (ensuring thegall bladder remained intact) at necropsy. The liver was then labelled and transported (within 4 hours) on ice to laboratory facilities.

3. The liver was laid on a smooth surface and was evaluated for gross pathological changes according to the morbid pathology score sheets.

4. Large bile ducts and gallbladder were dissected allowing the mature and larger immature fluke if present to be seen. These were counted and recorded on sheets. The balance of the liver tissue is dissected into 1cm thick slices and gently squeezed between the fingers. Any immature fluke appearing from the tissue were retrieved and countered. Remaining tissue was homogenised in a tissue "Stomacher" and washed over a 20 micron mesh such that any remaining immature flukes were recovered. The total worm counts were collated into the treatment groups.

Effective control was obtained against an established natural Fasciola hepatica burden with all formulations. The results are summarised on table 4 below.

Table 4: Total Worm Counts It can be clearly seen from the trials that the formulations of the present invention provide effective treatment of infection by the parasite Fasciola hepatica.

In addition the formulations of the present invention provide the advantage of increased stability over the previous suspension formulations.

The combination of increased stability and effective treatment against all stages of Fasciola hepatica is a real advantage. It allows the storage of formulation for long periods as may arise in veterinary practises or on the farm eliminating wastage. In addition it eliminates the problems caused by settling of actives. The maintenance of the actives in solution and therefore maintaining a uniform concentration across the formulation ensuring an effective safe dose on application at the recommended dosage.

ADVANTAGES

It is advantageous to be able to provide triclabendazole in stable solutions which can be more easily and effectively administered by pour-on. These solutions also allow the use of triclabendazole in combination with other anthelmintics resulting in broader spectrum of activity, and consequently a reduction in the number of treatments required. Now that triclabendazole can be dissolved to form a stable pour-on solution the opportunities for combining this effective anthelmintic with other actives in stable solutions have substantially increased.

Comparative Example Pour-on formulations are generally administered in small volumes; indeed conventional dosing guns for administering a pour-on usually deliver up to about quantities of a formulation. For treatment of fasciolosis by triclabendazole pour-on, a dosage form of 50ml can require a drug loading of more than 10% w/v. It is known that triclabendazole has solubility in absolute ethanol of about 0.2g per In order to achieve a suitable systemic concentration of triclabendazole, a 12% w/v drug loading would require dosing an animal with about 750 ml of ethanol including 6g of triclabendazole. At such volumes the dosing form may no longer constitute an effective pour-on since such dosing with such quantities has the effect of exiting the skin.

In view of the comparative example, the present invention allows farmers to substantially avoid the need for administering an impractically large single dose or repeated administration of a smaller dosage form. In any case farmers seek to avoid the need for multiple dosing and the exposure of animals to excessive volumes of carrier which may cause skin irritations. In addition with usage of larger volumes of a pour-on formulation it is difficult to prevent the dose from running off an animals hide.

The pour-on formulation of the present invention provides effective permeation through an animal's dermal layer without exposing the animal to excessive volumes of solvent. Indeed the present invention allows for administration of manageable dosing quantities without causing skin irritation, while achieving therapeutic concentrations of TCBZ at the liver. Hence the possibility for developing drug resistance is substantially obviated.

VARIATIONS

It is envisaged that the formulations are the subject of the invention may be modified.

by the inclusion of additional excipients without departing from the spirit and scope of the invention.

In particular it may be desirable to include dyes in the formulation to allow easy identification of treated animals. Alternately other excipients such as buffers, thickeners, spreading agents may be included to modify the formulation to specific animals.

In this specification the words "includes", "including" and the like and "comprises", "comprising" and the like should be considered synonymous and be given a nonexhaustive meaning.

Finally it will be appreciated that various other alterations and modifications may be made to the foregoing without departing from the scope of the invention.

Claims (4)

1. A pour-on veterinary anthelmintic formulation containing one or more anthelmintic actives wherein the anthelmintic active or one of the anthelmintic actives is triclabendazole or a pharmaceutically acceptable salt thereof and the triclabendazole is in a stable liquid solution, and wherein the solution contains at least 20% w/v of triclabendazole and a solvent system containing one or more of solvents selected from the group consisting of benzyl alcohol, glycerol formal, n-methyl-2-pyrrolidone, and glycol ethers.

2. A pour-on veterinary formulation as claimed in claim lwherein the solvent system contains at least two or more of the solvents selected from the group claimed in claim 1.

3. A pour-on veterinary formulation as claimed in claim 2, wherein the majority solvent in the solvent system is a glycol ether.

4. A pour-on veterinary formulation as claimed in claim 4, wherein the glycol ether is butyl dioxitol. A pour-on veterinary formulation as claimed in any one of claims 2 to 4, wherein a second solvent in the solvent system is benzyl alcohol. PIPERS MILLS OAKLEY Patent Attorneys for Ashmont Holdings Limited 9 March 2005