IES20070395A2 - A process for the preparation of a stable anhydrous anthelmintic formulation - Google Patents

Abstract

The present invention is directed to an industrial scale process for preparing a stable anhydrous anthelmintic liquid formulation containing ivermectin. The process comprises the steps of purging the manufacturing vessel with nitrogen gas, altering the pressure of the manufacturing vessel, rinsing the manufacturing vessel with isopropyl alcohol, adding isopropyl alcohol, Ivermectin and a fatty acid ester emollient, mixing, testing the solution, adding a buffering agent mixing, testing the solution, making up the total volume of the solution to 100 percent v/v with isopropyl alcohol and mixing and packaging the formulation. The formulation of the present invention is used for topical administration as a pour-on formulation.

Description

The present invention is directed to an industrial scale process for preparing a stable anhydrous anthelmintic formulation containing ivermectin. The formulation of the present invention is used for topical administration as a pour-on liquid formulation.

Background to the Invention Ivermectin is an antiparasitic agent, an anthelmintic, with a broad spectrum of activity against nematode worms and ectoparasites in animals, and has been in use for nearly a decade. It is effective against most common intestinal worms, most mites, and some lice. While normally used to treat animals, it is also prescribed to humans to treat infections of Strongyloides stercoralis and onchocerciasis (river blindness).

Ivermectin is chemically related to the insecticide avermectin. Both ivermectin and avermectin are derived from the bacterium Streptomyces avermitilis. Ivermectin has the following general formula: 070395 -2X..

W>yΑ.'.ινντίΓΐ’.ϊιη 9.t Ή,—fl Ϋ! t HZ I ! «X <.H M£T H -C / · / c < Ac , / . a H . i *· V1 (A/V I 1 ! >·· 73,35- if trcm eq51.

' Y' ·}« ·<Τ rl Ivermectin is a mixture of two components (5-o-demethyl-22,23-dihydroavermectin A1a) and (25-(1-methylethyl)-5-0-demethyl-25-de(1-methylpropyl)-22,23-dihydro5 avermection A1a). It is a white to yellowish-white crystalline powder.

Ivermectin acts by interfering with the target animal's central nervous system (CNS). However, at recommended doses, ivermectin does not readily penetrate the CNS of mammals. As such, ivermectin/avermectin formulations generally have low toxicity to humans. This means that although highly poisonous to insects, mammals, in particular humans, should not generally be adversely affected by normal use of avermectin pesticide formulations.

Ivermectin may be delivered in many different ways to treat various different 15 conditions. For example, Ivermectin may be delivered by the oral route to treat conditions in humans such as Onchocerciasis. Ivermectin tablets are generally used to achieve this aim as it is easy to control the dosage level in such unit dose forms.

Alternatively, Ivermectin may be delivered as an oral solution to animals via a dosing gun or as an injectable solution. A solution for oral ingestion will need to overcome 070395 -3the palatability problems associated with Ivermectin. Thus, it becomes apparent that each delivery method chosen for Ivermectin will need to overcome different problems.

Ivermectin solutions which are used as injectable solutions usually contain several ingredients such as alcohol, water and emulsifiers. There are many crucial aspects to this type of formulation as the resultant emulsion formulation depends on the fine balance between all ingredients. Furthermore, if such solutions are further diluted in water by the end user, the emulsion can be negatively affected and Ivermectin delivery with be detrimentally effected.

The present invention is concerned with a stable anhydrous topical formulation of Ivermectin, which is generally delivered to animals on mass using a pour-on system. This provides for the systemic delivery of Ivermectin to the bloodstream of the animal. However, there are several issues to be considered when making such a formulation on a large-scale.

Topical formulations of Ivermectin are known and include aqueous water based solutions, such as the synergistic combination formulation disclosed in US2006/0100165. However, such water based solutions are generally unsuitable for use as a pour-on as dilution with water impacts on the delivery of the correct dosage level of Ivermectin to the animal. The present invention is not concerned with such water containing formulations.

Other topical formulations are provided in the form of gels, ointments and creams for example. They can be used as shampoos for treating head lice and, as such, the need for the formulation to adhere to an area is crucial. Such formulations need specific ingredients to provide the formulation with the necessary properties, e.g. viscosity, for delivery of the correct dosage of Ivermectin to the animal. The present invention is not concerned with such formulations.

GB 2,403,905 is directed to a pour on formulation comprising a salicyiinlide together with avermectin in an alcohol solvent chosen from ethanol and isopropyl alcohol. Ideally, other constituents are present included PVP, PEG, emollients. This patent does not disclose the process for making the formulation. Furthermore, the polymeric moiety (PEG or PVP) is an essential feature of the invention which allows a higher quantity of the salicyiinlide to be dissolved in the formulation. Thus, this patent is 070395 -4directed to the problem of administering two active ingredients in the same formulation.

WO 01/60380 is directed to a combination formulation comprising Ivermectin and closantel. This patent is directed to a different problem, that of providing an appropriate solvent solution comprising two solvents, suitable for making such a combination formulation. As such, the process steps outlined are specific to this problem associated with combinations of active ingredients.

The present invention is directed to a stable anhydrous topical formulation of Ivermectin for use as a pour on solution for animals.

There are additional problems to be overcome when formulating such a pour on Ivermectin anhydrous solution on a large scale. These are outlined below.

Pure avermectin formulations are highly toxic to both insects and mammals. Furthermore, some dog breeds, for example the collie, exhibit signs of ivermectin related central nervous system toxicity at ivermectin doses generally exceeding 150 to 200 ug/kg. That is why commonly prescribed veterinary formulations of ivermectin used for heartworm prophylaxis limit dosages to the range of 6 to 12 ug/kg and are generally considered safe. Hence, it is crucial to ensure that the delivery system for Ivermectin to an animal provides the correct level of dosage of the active ingredient at all times even when the Ivermectin is delivered in aqueous solution as opposed to a unit dose form (e.g. a tablet) where the dosage of the active ingredient can be controlled.

Another problem associated with the large-scale manufacture of ivermectin formulations is that ivermectin is water insoluble. The preparation of formulations where the active ingredients are water insoluble provide problems when manufacturing on an industrial scale. The formulations must be readily and efficiently prepared and effective in use in that the Ivermectin must be present homogenously in the solution at the desired dosage level. Any slight differences in formulation may change the plasma kinetics and efficacy of the resultant formulation.

A further problem is that there is a need for a process for preparing a stable Ivermectin formulation. Stability is needed in order to allow for the formulation to be -5070395 prepared well in advance of their intended use. Again, the active ingredient must be homogenously distributed throughout the solution at all times during manufacture, packaging and storage prior to use. Long term stability of the solution, over a period of months and years, must be addressed in any such manufacturing process.

Furthermore, it is necessary to prepare a formulation ready for topical use which provides the active ingredient in a readily bioavailable form for systemic delivery. This allows for easier administration to the animals, particularly in the case of a large herd of large animals.

Thus, there is a need to develop an industrial large-scale process for the preparation of ivermectin topical or pour-on formulations which deals with these problems.

Statement of the Invention According to a first aspect of the invention, there is provided a process for the preparation of a topical anhydrous anthelmintic formulation with a pH of from 5 to 7 containing an effective amount of Ivermectin, wherein the process is carried out in a manufacturing vessel having a capacity of at least 3000 litres, the manufacturing vessel having additive vessels for adding the powder and liquid ingredients and a magnetic stirrer, the process comprises the steps of: a) Purging the manufacturing vessel with nitrogen gas; b) Increasing the pressure in the manufacturing vessel from approximately 0.2bar to approximately 3.75 bar; c) Reducing the pressure in the manufacturing vessel from approximately 3.75 bar to approximately 0.2 bar in 3 cycles; d) Rinsing the manufacturing vessel with isopropyl alcohol; e) Adding isopropyl alcohol in the range of 60 to 80% v/v to the manufacturing vessel; 070395 -6f) Adding Ivermectin in the range of 0.1% to 5% w/v and mixing with agitation for approximately 5 to 20 minutes at a low speed of approximately 100 to 150 rpm: g) Adding a fatty acid ester emollient mixture comprising cetearyl Ethylhexanoate and Isopropyl Myristate in the range of 15% to 25% v/v and mixing for approximately 1 to 20 minutes at a low speed of approximately 100 to 150 rpm; h) Removing a sample of the solution obtained from step (g) for visual assessment of ivermectin dissolution and mixing at a low speed of approximately 100 to 150 rpm until the ivermectin has completely dissolved; i) Adding the buffering agent triethanolamine in the range of 0.01% to 1% v/v and mixing for approximately 2 to 15 minutes; j) Removing a sample of the solution obtained from step (i) for visual assessment of ivermectin dissolution and mixing at a low speed of approximately 100 to 150 rpm until dispersion is complete; k) Making up the total volume of the solution to 100% v/v with isopropyl alcohol and mixing for a further approximately 5 to 15 minutes at a low speed of approximately 100 to 150 rpm; l) Obtaining a sample of the solution obtained from step (k) from the top, middle and bottom of the vessel, sending the samples to be assessed for quality control and awaiting approval from quality control; and m) Mixing the solution for a further 5 to 20 minutes directly prior to packaging the formulation obtained from step (k) into containers.

The process of the present invention provides an anhydrous topical formulation with the ability of the active ingredient, Ivermectin, to transfer into the bloodstream and produce an efficacious homogenous dose of the active ingredient when administered to an animal as a pour on formulation. Previously, homogenous distribution and delivery of the correct dosage level of Ivermectin has been hampered due to the fact 070395 -7that Ivermectin is insoluble. Ivermectin can have severe adverse effects at incorrect dosage levels.

In addition, the process and excipients used provide a formulation which has long term stability. This is important when manufacturing on an industrial scale.

Furthermore, the formulation of the present invention only contains the active ingredient, an alcohol solvent, a fatty acid ester emollient and a buffering agent. This is in direct contrast to many other formulations which are complicated and contain many ingredients which if not added at the correct level and in the correct manner can adversely affect the ability of the formulation to deliver the active ingredient correctly. On the contrary, the present invention limits the number of ingredients used in the formulation and provides a straightforward and easy to apply process for use on an industrial scale. This is one of the major advantages of the present invention.

Detailed Description of the Invention In the specification the term “by weight” refers to the weight of the final composition and “by volume refers to the volume of the final composition. The term “effective amount” refers to the amount of the active ingredient needed to destroy parasites.

The industrial large-scale manufacture of any drug presents the pharmaceutical manufacturer with many issues to consider.

In the large-scale manufacture of a formulation, it is essential that the entire batch being manufactured meets the various criteria set by regulatory legislation and there must be little or no product variation within a batch.

Product variation is usually attributed to segregation of the ingredients, in particular the active ingredient, within a batch. This is an unpredictable or random event. If product variation is found within a batch, this could result in the batch not meeting the required standards and the subsequent wastage of an entire batch. This is expensive and time-consuming and something a pharmaceutical manufacturer will avoid. This is also a particular problem when delivering Ivermectin in a solution. Any process must ensure the resultant solution has a homogenous dispersion of ivermectin. If not, delivering the correct dosage of active ingredient is not possible. 070395 -8The present invention is directed to solving these manufacturing problems and the other problems outlined above when making an ivermectin formulation on a largescale.

In general terms, the process and formulation produced according to the invention provides a robust, simple process for producing a formulation of good quality with good short and long term stability results. Furthermore, the process provides for a product with a homogenous distribution/dispersion of Ivermectin in solution.

Specifically, the process of the invention provides process for the manufacture of a formulation which has good uniformity when manufactured on a large-scale and is a homogenous liquid where the components are uniformly distributed throughout the mixture and Is shelf stable.

The manufacturing vessel used in the present invention should be attachable to a powder charging vessel/hopper and a liquid charging vessel. The manufacturing vessel should ideally have a capacity of up to 4000 litres. The powder charging vessel should have a capacity ideally of at least 20 litres and the liquid charging vessel should have a capacity of ideally approximately 5 litres. The manufacturing vessel must be capable of achieving containment of a micronised powder.

The manufacturing vessel may be made from conventional stainless steel or other materials may be used.

In order to ensure that there Is no residual water and the resultant formulation is anhydrous, the following specific steps must be earned out in this order.

The manufacturing vessel requires a nitrogen supply to aid in the prevention of an explosion by purging the equipment with nitrogen gas. Nitrogen gas is an inert gas which shields a product from atmospheric oxygen and moisture. Nitrogen blanketing during the manufacturing, holding and filling periods is essential and nitrogen pressurization to remove oxygen before rinsing the manufacturing vessel with isopropyl alcohol is required. The nitrogen gas forces air out of the manufacturing vessel and provides a protective environment during start-up and shut-down 070395 -9Furthermore, the manufacturing vessel must be provided with two pressure supplies. The maximum vessel pressure is 3.75 bar. Ideally, one pressure supply is set at approximately 2.0 bar gauge for inerting and one low pressure supply is set at approximately 0.2 bar gauge for purging. Pressure must be controlled at an accuracy of +/-10%. This step provides an advantage in terms of safety of the process.

The manufacturing vessel also contains a magnetic drive mixer which must achieve the required mixing in the vessel range of 300 litres to 4000 litres. The advantage of using a magnetic mixture is that no mechanical sealing is required either internally or externally on the manufacturing vessel.

During the manufacturing process, it is a requirement that samples are taken to ascertain the effectiveness of the vessel mixer. These monitoring steps are crucial to the batch manufacturing process of the present invention and must be carried out at each step of the process.

The resultant formulation made by the process of the present invention is an Ivermectin solution which is suitable for administration as a pour-on to deliver the active ingredient for systemic effects.

An essential step in the manufacture of such an anhydrous formulation is the initial step of purging the manufacturing vessel with the solvent, isopropyl alcohol. This ensures that there is no water present in the manufacturing process. This is essential as the formulation is an anhydrous or non-aqueous formulation.

Furthermore, the process of the present invention provides for a safe, easy to administer application form which makes possible a more exact topical therapy for systemic administrations than could previously be achieved. Clinical studies have shown that sufficient levels of ivermectin are achieved after administration of the topical anhydrous solution of the invention to the target animal.

Furthermore, as this is a pour on solution it is important to ensure the viscosity of the solution is appropriate for this type of administration and that the viscosity of the solution is within the range needed to allow for systemic delivery of the active ingredient. Again, the choice of excipients ensures the correct viscosity is maintained within the solution. Ideally, the viscosity of the product of the invention is from 070395 -10approximately 40 to 80 centiposie (cP) and/or from approximately 5 to 25E Torque.

The components of the topical formulation are discussed in detail below.

Ideally, isoproroyl alcohol Ph Eur. or propan-2-ol conforms to the monograph of the European Pharmacopoeia 01/2005:0970. It is used as primarily as a solvent. Preferably, isopropyl (IPA) is added at a level of from 65 to 75% v/v.

Ideally, Ivermectin Ph Eur. conforms to the monograph of the European Pharmacopoeia 01/2005:1336 and as defined above is a mixture of two components (5-o-demethyl-22,23-dihydroavermectin Aia) and (25-(1-methyiethyl)-5-O-demethyl25-de(1-methylpropyl)-22,23-dihydroavermection A1a). It is a white to yellowish-white crystalline powder.

Preferably, Ivermectin is added at a level of approximately 0.5% v/w. The weight is determined by the dosage level needed in the resultant topical solution.

As this formulation is a pour-on formulation, an emollient is required to give the formulation the necessary properties for topical administration such as good wetting and stiffening/spreading properties. The emollient used in the present invention is a mixture of fatty acids, preferably cetearyl ethylhexanoate and Isopropyl Myristate. Cetearyl ethylhexanoate comprises stearyl octanoate and cetyl octanoate. Other fatty acid esters may be contemplated.

Preferably, the emollient is used at a level of approximately 20 v/v.

The following is the typical fatty acid profile of crodamol cap™ (super refined) which may be used as an emollient according to the invention: Isopropyl myristate: 9.0%, Cetyl Octanoate 68.5%, Stearyl Octanoate 21.6% and others 0.9%. Crodamol Cap™ can also act as a viscosity modifier and a solubilizer.

A buffering agent is used which may be any conventional buffering agent used in this field. Ideally, Triethanolamine Ph Eur. 01/2005:1577 is used which is a buffer conforms to the monograph of the European Pharmacopoeia. Triethanolamine or trolamine is 2,2’,2’’-nitrotriethanol. Other conventional buffers will be understood to be within the scope of the present invention. The use of the buffering agent is an 070395 -11 essential step of the invention which provides a desired pH for Ivermectin delivery. Furthermore, it advantageously aids the permeation properties of the topical formulation.

Preferably, triethanolamine is used at a level of 0.05% v/v to achieve a pH of approximately 5 to 7. As this is a topical solution for use with animals, a pH of this range is essential i.e. neutral pH.

It will be understood that other emollients, buffers and solvents generally used in the pharmaceutical field may be used in the process of this invention.

The formulation of the invention may be applied in the veterinary field, for combating endoparasites and ectoparasites affecting animals such as bovines and equines.

The invention will now be described by reference to the following non-limiting examples and figures.

Figure 1 shows a process outline for preparing a 180 litre ivermectin formulation; Figure 2 shows a process outline for preparing a 1,500 litre ivermectin formulation; and Figure 3 shows another process according to the invention.

As shown in Figures 1,2 and 3, the general method involved the steps of sequentially adding the ivermectin, emollient, buffering agent e.g. triethanolamine to at least part of the solvent isopropyl alcohol.

The steps of purging the manufacturing vessel with nitrogen and pressurizing the vessel from approximately 1 bar to approximately 0.2 bar are not shown. These steps occur prior to the addition of the alcohol solvent to the manufacturing vessel.

After each ingredient is added, the mixture is mixed in a stainless steel manufacturing vessel at a slow speed until the ivermectin in the formulation is completely dissolved and dispersed in the solution. -12070395 The final step involves adding the remaining isopropyl alcohol and carrying out a final mixing step.

The formulation is then subject to quality control analysis and samples from defined areas of the formulation are obtained and tested to ensure they comply with the inprocess bulk testing specifications. Visual inspection and HPLC analysis may be carried out to assess whether the formulation complies with the in-process bulk testing specification outlined in the examples.

By adding the excipients in this manner, the preparation time is minimised as there is substantially no entrainment of air in the mixture. Thus, settlement time between additives is not required. The production process is optimised as the production time is minimised.

After a batch is complete, the manufacturing vessel and various additive vessels and lines may be easily disconnected and cleaned in-situ.

Once the formulation has passed the quality control tests, it is then passed to the packaging station, where it is filled through a liquid filler into containers. The closures are screwed on and the appropriate labels with batch numbers etc are added. The containers are then placed in outer cartons and then sealed.

Figure 3 shows a variation on the process of the invention, with the steps of purging the manufacturing vessel with nitrogen and pressurizing the vessel from approximately 1 bar to approximately 0.2 bar which occur prior to the addition of the alcohol solvent to the manufacturing vessel. The remaining steps are as defined in relation to Figures 1 and 2. 070395 Example 1: Ivermectin Formulation The following table shows a typical ivermectin solution prepared according to the present invention which is suitable for topical administration: Ingredient Quantity and/or Percentage Function Reference to standard Active Substance: Ivermectin 0.5% w/v Active ingredient Ph. Eur. Excipients: Crodamol Cap™ Triethanolamine Isopropyl alcohol 20.00% v/v 0.05% v/v q.s. 100.0% v/v Emollient Buffer Solvent Product spec. Ph. Eur. Ph. Eur.

Example 2: Manufacturing Process Equipment Required: Ail the equipment used in carrying out the process is well known equipment and does not need further description.

A conventional stainless steel vessel such as a pressure vessel PET 3 group 4, with an internal finish below 0.4RA may be used. The stainless steel vessel is provided with a magnetic stirrer and various inlets and outlets for the addition of active ingredient power and liquid excipients. The vessel is also connected to a nitrogen gas source for nitrogen purging and pressurization.

Method 1a: Manufacture of 180L Batch size The following steps were carried out: 1. Fill approx. 130L of Isopropyl alcohol into the manufacturing vessel; 2. Add Ivermectin and mix for approximately 5 min; 070395 -143. Add Crodamol Cap™ and mix for approximately 5 min; 4. Add Triethanolamine and mix for approximately 3 min; . Bring to 180L mark with Isopropyl alcohol and mix for approximately 5 min; 6. The bulk solution is sampled from the top, middle and bottom of the tank and sent to quality control (QC) for analysis.

The times used in the above method are by means of example only and variations +/10 minutes are also contemplated.

Method 2a: Manufacture of 1500L Batch Size The following steps were carried out: 1. Fill approx. 850Kg of Isopropyl alcohol into the manufacturing vessel; 2. Add Ivermectin and mix for approximately 5 min. at low speed; 3. Add Crodamol Cap™ and mix for approximately 15 min. at low speed; 4. Mix for a further approximately 15 min. at low speed; . Remove 100ml sample for visual assessment of ivermectin dissolution. If ivermectin is not completely dissolved mix for a further 15min. at low speed; 6. Add Triethanolamine and mix for approximately 10 min. at low speed; 7. Remove 100ml sample for visual assessment of dispersion. If dispersion is not complete mix for approximately a further 10 min. at low speed; 8. Bring to 1500L with Isopropyl alcohol and mix for approximately 20 min. at low speed; 9. Prior to filling samples of the bulk product are taken form the top, middle and bottom of the tank and sent for QC analysis. Tests and specifications are as per the following table: The times used in the above method are by means of example only and variations +/10 minutes are also contemplated. 070395 -15In-Process Bulk Testing Specifications: Test Specification Appearance A clear colourless solution with a characteristic odour Ivermectin Assay (% w/v) 0.5% w/v (5% limit) Range: 0.475 - 0.525% w/v Related Substances Known impurities RRT 1.3 to 1.5: <3% All other known impurities: <2% Any unknown impurity: <1 % Total impurities: <6% Identification HPLC: The chromatography of the assay exhibits major peaks due to Ivermectin, the retention time of which corresponds to that exhibited in the chromatogram of the standard preparation.

Method 1 b/2b : Packaging Procedure The following steps were carried out: 1. The formulation is cleared by QC and packaging materials are issued; 2. The containers are filled via the liquid filler 3. A container number check is made to establish the batch yield and to reconcile the theoretical versus the actual yield; 4. The appropriate number of labels is requisitioned from the quality control department and recorded on the packaging documentation along with the manufacturing date, batch numbers, label numbers, reconciliation and signature of the individual responsible; . The closures are screwed onto the containers and the labels applied; 6. The containers are placed in outer cartons and the cartons sealed; 7. The cartons are palletised and placed in the finished product quarantine area for final inspection. ®70395 -16Example 2: Stability Results for Ivermectin Formulation Stability data of the two batches of the product manufactured according to Example 5 1a after 3 years is presented in the following tables (Part I (0-10 months)) and Part II (12-36 months)): PRODUCT STRENGTH PACK BATCH SIZE STORAGE CONDITIONS Ivermectin Pour-On 0.5%w/v Ivermectin 1L Flat Bottomed Flexl Pack 180L Temp: 25C/60%RH Parti: Specification Initial 4 mths 7 mths 9mths 10mths Appearance A clear colourless solution with a characteristic odour. Conforms Conforms Conforms Conforms Conforms Condition of Packaging Packaging intact Conforms Conforms Conforms Conforms Conforms Identification Conforms Conforms Conforms Conforms Conforms Conforms Assay Active Ivermectin 0.5%w/v ± 5% i.e. 0.475%w/v - 0.525%w/v 0.508% 0.484% 0.495% 0.502% NP 070395 -17Part II; Specification 12 mths 18 mths 21 mths 30 mths 36 mths Appearance A clear colourless solution with a characteristic odour. Conforms Conforms Conforms Conforms Conforms Condition of Packaging Packaging intact Conforms Conforms Conforms Conforms Conforms Identification Conforms Conforms Conforms Conforms Conforms Conforms Assay Active Ivermectin 0.5%w/v ± 5% i.e. 0.475%w/v - 0.525%w/v 0.490% 0.516% 0.485% 0.484% 0.484 ND.Not Detected 5 NP:Not Performed At several intervals during this time the formulation was analyzed and compared to the in-process bulk testing specifications outlined below.

Results are shown in the table below. 070395 PRODUCT STRENGTH PACK BATCH SIZE STORAGE CONDITIONS Ivermectin Pour-On 0.5%w/v Ivermectin 1L Flat Bottomed Flexi Pack 180L Temp: 4O’C/75%RH Test Specification Initial 3 mths 6 mths 10 mths 12 mths 18mths Appearance A clear colourless solution with a characteristic odour. Conforms Conforms Conforms Conforms Conforms Conforms Condition of Packaging Packaging intact Conforms Conforms Conforms Conforms Conforms Conforms Identification Conforms Conforms Conforms Conforms Conforms Conforms Conforms Assay Active Ivermectin 0.5%w/v ± 5% i.e. 0.475%w/v - 0.525%w/v 0.508% 0.488% 0.495% NP 0.485% 0.507% ND: Not Detected NP: Not Performed It can be seen in the above tables that the Ivermectin pour-on produced in accordance with the present invention was stable over two separate trials for a period of 36 and 18 months respectively. Furthermore, the Ivermectin was active at all times during this test period.

Thus, the process defined in Example 1 provides a stable, homogenous, anhydrous ivermectin solution which is shelf stable over at least a 3 year period. β703«,5 -19The viscosity of the product made in accordance with Example 1 was measured using a Brookfield viscometer (settings Spindle 1 and speed 5100) and the following results were obtained: Viscosity: 63.1 Cp Torque: 15.71 E Finally, clinical studies on target species have also shown that after administration the product is absorbed at a level to provide excellent efficacy of the active ingredient, Ivermectin.

Example 3 - Bio-equivalence studies The pharmacokinetics of the product manufactured according to Example 1 and 15 Ivomec® Classic Pour-On for cattle, were compared in the target species, cattle.

The products were shown to be bioequivalent within 90% confidence limits and within the 80 - 125% established in the Guideline EMEA/CVMP/016/00 (Guidelines for the conduct of the bioequivalence study for veterinary medicinal products). On this basis, Ivermectin Pour-On is considered to be essentially similar or bioequivalent to Ivomec® Classic Pour-On for cattle.

The present invention provides a new method suitable for industrial use for a new ivermectin pour on formulation with only four essential and well-defined components.

The study conducted was a two-way, single dose, crossover blood bio-equivalence trial to determine the comparative plasma ivermectin concentrations in cattle following treatment with the product manufactured according to Example 1 (Ivermectin Pour-On) and the reference product (Ivomec® Classic Pour-On for Cattle).

This bioequivalence study was performed in accordance with the principles of GCP and GLP at a GLP approved facility. The test and reference products are indicated for cattle of all ages. i 070395 -20In this study, twenty-four male, 8 month-old Friesian cattle, weighing between 296 kg and 390 kg were allocated into two groups by restricted randomisation based on pre-study bodyweight to ensure homogenous groups. Following an acclimatisation period of 7 days, each animal was administered topically either the test or reference product (determined by group allocation) at a dose rate of 500 pg ivermectin per kg bodyweight.

The crossover design is summarised below: Group I Phase I Reference (Days 0-42) Ivomec® Classic Pour-On Group II Test Ivermectin Pour-On Phase II (Days 72-114) Test Ivermectin Pour-On Reference IvomecOCIassic Pour-On Serial blood samples were collected from the jugular vein of each animal before and after product administration at the following times: Days (Phase l/Phase II) Day -1/71 0/72 1/73 2/74 3/75 4/76 5/77 6/78 Times of extraction (hours post dose) Basal 6, 12 24, 36 48, 54, 60 72, 78, 84 96, 102, 108 120, 126, 132 144 Days (Phase l/Phase II) Day 7/79 9/81 14/86 21/93 28/100 35/107 42/114 Times of extraction (hours post dose) 168 216 336 504 672 840 1008 Each phase of the study lasted 42 days from the first day of treatment with a “wash-out period of 72 days between the administration of the products in Phases 0 39 5 -21 I and II. The “wash-out” period was determined based on at least 10 times the terminal half-life of the active. The terminal half-life of Ivermectin following administration as a pour-on to cattle at the recommended dose rate was determined as approximately 5.3 ± 1.8 days i.e. a maximum of 7.1 days or 170.4 hrs, (V. Gayrard et al 1999). After 72 days each animal was again administered either the test or reference product in an identical manner, with the product-togroup treatment being reversed. Serial blood samples were again collected for analysis of plasma ivermectin concentration as described in the tables above.

All animals were clinically examined prior to and during the trial and were observed daily for any signs of ill-health or intolerance to the product, including application site reactions. No evidence of intolerance to either test or reference products was noted.

Serial blood samples were centrifuged and the plasma frozen for transport to the analytical laboratory immediately after collection. Analysis of the blood samples for Ivermectin concentration was performed using a fully validated H.P.L.C. method.

The pharmacokinetic profile of Ivermectin in cattle following administration of either test or reference products is characterised by a sharp rise in plasma Ivermectin concentration, followed by a slow depletion phase.

The bioequivalence of the test and reference products was determined by calculating the confidence limits of the difference of the two means. The confidence intervals for the quotient of the means from log-transformed data are the following: Variable Lower Limit (%) Upper Limit (%) Cmax 85.20% 116.65% AUC 96.55% 112.88% The study concluded that the Ivermectin product manufactured according to Example 1 is bioequivalent to the reference item Ivomec® Classic Pour-On for Cattle since the confidence interval for AUC and Cmax of the difference between the test and reference items is within the interval 80-125% established in the Guideline EMEA/CVMP/016/00 (Guidelines for the conduct of the bioequivalence study for veterinary medicinal products). -22ln the specification, the terms “comprise, comprises, comprised and comprising” and any variation thereof and the terms “include, includes, included and including” and any variation thereof are considered to be totally interchangeable and they should all be afforded the widest interpretation.

The invention is not limited to the embodiments described above but may be varied within the scope of the claims.

Claims (5)

1. A process for the preparation of a stable topical anhydrous liquid anthelmintic formulation with a pH of from 5 to 7 containing an effective amount of ivermectin, wherein the process is carried out in a manufacturing vessel having a capacity of at least 3000 litres, the manufacturing vessel having additive vessels for adding the powder and liquid ingredients and a magnetic stirrer, the process comprises the steps of: a) Purging the manufacturing vessel with nitrogen gas; b) Increasing the pressure in the manufacturing vessel from approximately 0.2bar to approximately 3.75 bar; c) Reducing the pressure in the manufacturing vessel in 3 cycles from approximately 3.75 bar to approximately 0.2 bar; d) Rinsing the manufacturing vessel with isopropyl alcohol; e) Adding isopropyl alcohol in the range of 60 to 80% v/v to the manufacturing vessel; f) Adding Ivermectin in the range of 0.1% to 5% w/v and mixing with agitation for approximately 5 to 20 minutes at a low speed of approximately 100 to 150 rpm; g) Adding a fatty acid ester emollient comprising cetearyl ethylhexanoate and Isopropyl Myristate in the range of 15% to 25% v/v and mixing for approximately 1 to 20 minutes at a low speed of approximately 100 to 150 rpm; h) Removing a sample of the solution obtained from step (g) for visual assessment of ivermectin dissolution and mixing at a low speed of approximately 100 to 150 rpm until the ivermectin has completely dissolved; 3 9 5 -24i) Adding a buffering agent in the range of 0.01% to 1% v/v and mixing for approximately 2 to 15 minutes; j) Removing a sample of the solution obtained from step (i) for visual 5 assessment of ivermectin dissolution and mixing at a low speed of approximately 100 to 150 rpm until dispersion is complete; k) Making up the total volume of the solution to 100% v/v with isopropyl alcohol and mixing for a further approximately 5 to 15 minutes at a low 10 speed of approximately 100 to 150 rpm; l) Obtaining a sample of the solution obtained from step (k) from the top, middle and bottom of the vessel, sending the samples to be assessed for quality control and awaiting approval from quality control; and m) Mixing the solution for a further 5 to 20 minutes directly prior to packaging the formulation obtained from step (k) into containers.

2. The process according to claim 1 wherein cetearyl ethylhexanoate is a 20 mixture of stearyl octanoate and cetyl octanoate.

3. The process according to claim 1 or claim 2 wherein the buffering agent is triethanolamine. 25

4. The process according to any of the preceding claims wherein the stable topical anhydrous liquid formulation has a viscosity from approximately 40 to 80 cPs.

5. The process according to any of the preceding claim wherein the sample 30 obtained from steps (h), (j) and (I) are subjected to HPLC analysis.