WO2003051116A1

WO2003051116A1 - Microencapsulated insecticide

Info

Publication number: WO2003051116A1
Application number: PCT/IB2002/005766
Authority: WO
Inventors: Miguel Gimeno; Barbara Gimeno
Original assignee: Mars, Incorporated
Priority date: 2001-12-14
Filing date: 2002-12-16
Publication date: 2003-06-26
Also published as: GB0129976D0; AU2002366286A1

Abstract

The present invention provides a microencapsulated insecticide which is prepared by oil-in-water interfacial polymerisation, wherein said insecticide is a solid insecticide at room temperature and pressure and having limited solubility in organic solvents. Various delivery systems for delivering the microencapsulated to a companion animal are also described. A preferred delivery system is an organic dispersion of the microencapsulated insecticide, wherein an oil-in-water-in-oil emulsion is prepared by emulsifying the product of the interfacial oil-in-water polymerisation method in a continuous organic phase.

Description

MICROENCAPSULATED INSECTICIDE

This invention relates to the treatment of infestation in animals by ectoparasites, such as fleas and ticks.

All publications, patents and patent applications cited herein are incorporated in full by reference.

Infestation by fleas and ticks is a common problem in domesticated animals. It is a particular problem in companion animals ("pets") where the presence of fleas and ticks in the home is highly undesirable for reasons of hygiene.

Hence, there are many commercially available treatments for controlling infestation of pets. Generally, these methods comprise an insecticide in a delivery system, such as a spray, shampoo, collar, drops or powder.

A problem with these conventional systems is that in order to achieve a dose that is effective in killing the infesting ectoparasite, the insecticide must be used at a level that is toxic to the animal itself. Although many highly efficacious insecticides, such as deltamethrin, are known in the art, their use in pet applications has been limited, since these insecticides have unacceptably high oral and topical toxicity.

The toxicity of the insecticide to the animal, either from ingestion or in hypersensitisation reactions on the animal's skin, is thus an important factor in determining the suitability of an insecticide. One commonly used insecticide is permethrin, a synthetic broad-spectrum insecticide which is known to have relatively low oral and topical toxicity. Permethrin has thus been used widely in commercially available treatments, but its suitability is related to the rate of delivery required to provide efficacy. Such rate requirements limit the use of delivery systems to those capable of delivery of high topical concentrations.

WO98/57540 describes a pest control system comprising deltamethrin. The deltamethrin is entrapped in a polymeric matrix which includes a triphenyl phosphate carrier. It is understood that entrapment of deltamethrin in this way does not provide sufficient control of its release onto the animal's skin. Therefore, triphenyl phosphate is necessary since it acts as an anti-irritant and alleviates the topical toxicity of deltamethrin. Typically, the pest control system is a dog collar made from polyvinyl chloride impregnated with deltamethrin. A further problem with current pet treatments is that many of the currently-available systems require repeat treatments at regular intervals in order to control infestation. The repeat treatments may be needed as often as once per week in some cases. The administration of repeat treatments is undesirable. From the owner's point of view, administration of the treatment is time-consuming and difficult, whilst the pet often finds the administration of the treatment a distressing experience. Furthermore, the burden of the requirement for regular administration of treatments often means that pet-owners are not vigilant in controlling ectoparasite infestation in their pets.

It would be desirable to be able to use a highly efficacious insecticide on animals, whilst mitigating against its toxic side-effects.

It is an object of the present invention to provide an insect treatment for domesticated animals which does not require repeat treatments at regular intervals. It is a further object of the present invention to provide an insect treatment which can be used with highly efficacious insecticides whilst minimising the risk of toxicity to the animal receiving the treatment.

Accordingly, the present invention provides a microencapsulated insecticide which is prepared by oil-in-water interfacial polymerisation, wherein at room temperature and pressure, said insecticide is a solid insecticide having limited solubility in organic solvents.

The polymerisation method used to generate the microencapsulated insecticides of the present invention provides an insecticide enclosed by a polymeric wall from which the insecticide is released over a period of time. The insecticide is released from the microcapsule in a substantially zero-order diffusion process.

When the microcapsule contains a material of low solubility, a saturated solution is formed inside the microcapsule. When more liquid enters, the saturated solution is maintained as long as a reservoir of insoluble material remains inside the microcapsule. During this period of time the concentration gradient across the capsule wall, and hence the release rate is constant. Hence, the release kinetics of the microcapsule are "zero-order", by analogy with chemical reactions (ENCYCLOPEDIA of Chemical Processing and Design; John J.McKetta and William A.Cunningham, Marcel Dekker, Inc. 1989). Zero-order diffusion of the insecticide is highly advantageous for a number of reasons. First, it avoids an initial high concentration of insecticide being delivered to the animal's skin, thus minimising toxicity to the animal. Second, zero-order release allows the delivery of an efficacious level of insecticide to the skin of an animal for a longer period of time than conventional treatments allow, without resulting in significant irritation to the animal's skin. A further advantage of the present invention is that by microencapsulating the insecticide, the vapour pressure of the insecticide is dramatically reduced. Thus, undesirable inhalation of the insecticide is also avoided, both by the treated animal and by bystander animals/ animal owners.

In contrast, the delivery of non-microencapsulated insecticide to the animal occurs following first-order kinetics, characterized by an exponential decrease of concentration.

Further, in some microencapsulated formulations, first order release occurs when the microcapsules contain a highly soluble material, forming a highly concentrated solution inside the capsules. When more liquid enters, the solution diffuses out and the concentration inside the capsules decreases, lowering the concentration gradient across the wall and slowing the release rate. The release rate decreases exponentially in a first order release pattern, analogous to the change in reaction rate for a first order chemical decomposition (ENCYCLOPEDIA of Chemical Processing and Design; John J.McKetta and William A.Cunningham, Marcel Dekker, Inc. 1989).

The microencapsulated insecticide of the invention thus allows highly efficacious insecticides that are characterised by low solubility in organic solvents and that are solid at room temperature and pressure, such as deltamethrin, to be used on animals, by delivering a constant and low dose of insecticide to the animal, which does not reach toxic levels.

Various processes for the microencapsulation of active ingredients are known in the art. These are described in, for example, EP-A-0165227, EP-A-0141584, US 3,624,248, US 3,492,380, US 4,102,800, US 4,436,719, US 4,497.793, US 4,563,212, US 4,160,838, US 4,285,720, US 4,230.809, US 4,303,548, EP-A-0214936 and WO97/18705. However, none of these methods allows the microencapsulation of an insecticide such as deltamethrin, which has limited solubility in organic solvents, by an oil-in-water interfacial polymerisation method.

The microencapsulated insecticides of the present invention are very different to the amorphous matrices of insecticide and binder material of the type described in WO98/57540. The prior art materials are not true microcapsules, in that they do not consist of an insecticide enclosed by a crosslinked polymeric wall prepared by interfacial oil-in- water polymerisation. Rather, these matrices consist of a mixture of the insecticide and binder components and do not, therefore, have the advantageous release properties of the present invention.

The microencapsulated insecticides of the invention may be used to treat any ectoparasite that causes undesirable infestation of a domestic animal. Typical ectoparasites are insects, such as fleas and mites, and arachnids such as ticks. Correspondingly, the term "insecticide" as used herein means any substance suitable for killing ectoparasites.

The insecticides used in the present invention have limited solubility in organic solvents. By limited solubility in organic solvents, it is meant a solubility of less than lOOg/l, preferably less than 75g/l, more preferably less than 50g/l in Solvesso 200 at room temperature. The insecticides are preferably highly efficacious.

Examples of insecticides which may be used in the present invention are EPN, Methidathion, Chlorpyrifos, Phosalone, Dimethoate, Methamidophos, Fenpropathrin, Salithion, Fenoxycarb, Azinphos-Ethyl, Azinphos-Methyl, MTMC, Methomyl, Xylylcarb, Cloethocarb, Trichlorfon, Acephate, Amitraz, MIPC, Propoxur, Aminocarb, Aldicarb, , Fipronil, Imidacloprid, Acetamiprid, Thiamethoxam, Clothianidin, Dinotefuran, Nitenpyram, Trimethacarb, Dioxacarb, Methiocarb, Bendiocarb, Vamidothion, Oxamyl and Hexythiazox.

The pyrethroid type (chrysanthemate type) of insecticides are preferred for use in the present invention. The pyrethroid type of insecticides include Acrinathrin, Allethrin, Alpha-Cypermethrin, Beta-cyfluthrin, Beta-cypermethrin, Bifenthrin, Bioallethrin, Bioallethrin S-cyclopentenyl isomer, Bioresmethrin, Cycloprothrin, Cyfluthrin, Cyhalothrin, Cypermethrin, Cyphenothrin [(lR)-trans.isomer] , Deltamethrin, Empenthrin[ (EZ)-(lR)-isomers, Esbiothrin, Esfenvalerate, Fenpropathrin, Fenvalerate, Flucythrinate, Flumethrin, Imiprothrin, Lamda-cyhalothrin, Permethrin, Phenothrin[(lR)- trans-isomer] , Prallethrin, Resmethrin, RU15525, Sumithrin, Tau-fluvalinate, Tefluthrin Tetramethrin, Tetramethrin [(lR)-isomer] , Theta-cypermethrin, Tralomethrin, Transfluthrin, Zeta-cypermethrin, ZXI8901, Etofenprox, Halfenprox and Silafluofen.

A particularly preferred insecticide used in the present invention is deltamethrin. This insecticide has a high efficacy in killing ectoparasites, yet is not toxic to domesticated animals at the dose required for ectoparasite knock-down. The present invention allows a dose to be delivered over a period of time that is non-toxic to the treated animal, yet which is toxic to infesting ectoparasites. By changing the properties of the microcapsules used in the insecticides of the invention, it is possible to change the release characteristics of the microcapsules and hence suit the type of microcapsule to the site of application of the drug and the proposed method of delivery. Factors which affect the release characteristics of the microcapsule are the thickness of the microcapsule shell wall, the composition of the cell wall, the degree of crosslinking, and the size of the capsule. Crosslinking is defined as 0 when only monomers with difunctional NCO groups are present and defined as 100 when only trifunctional isocyanates are present. Mixtures of difunctional and trifunctional isocyanates provide intermediate degrees of crosslinking, depending on the relative proportions of difunctional and trifunctional isocyanates.

Preferably, the microcapsule shell wall has a degree of crosslinking between 0 to 100, preferably between 75 to 25, and more preferably between 60 to 40, which provides the desired diffusion rate for the contained ectoparasiticide.

The polymeric shell wall may be prepared by reaction of polyamines with polybasic acid halides to form polyamide shells; diacid or polyacid chlorides with diamines or polyamines to form polyamide shells; polyamines reacting with bischloroforates to form polyurethane or polyether shells; dichloroformates or polychloroformates with diamines or polyamines to form polyurethane shells; diisocyanates or polyisocyanates reacting with diols or polyols to form polyurethane shells; polyphenols reacting with polybasic acid halides to form polyester type shells; diisocyanates or polyisocyanates reacting with diamines or polyamines to form polyurea shells; isocyanates reacting in situ to form polyurea shells; ureaformaldehyde reacting in presence of acid catalysts to form aminoplast shells; disulfonyl or polysulfonyl chlorides reacting with diamines or polyamines to form polysulfonamide shells; or dichloroformates or polychloroformates reacting with diols or polyols to form polycarbonate shells.

A preferred polymeric shell wall is prepared by isocyanates reacting in situ at elevated temperature to form polyurea shells.

Emulsions are heterogenous mixtures of at least one immiscible liquid dispersed in another in the form of droplets with a diameter greater than 0.1 microns. Oil in water (O/W) emulsions are formed when the water is the continous phase and the oil is the dispersed phase. Microencapsulation by interfacial condensation polymerisation involves bringing together two immiscible liquids, the oil- and the water-phase which form an emulsion. Oil in water emulsion polymerisation is taking place when the oil droplets are dispersed into the continuous water phase and the capsule wall is formed at the interface creating a polymeric shell around the oil phase.

Preferably, the shell wall of the microencapsulated insecticides of the invention is formed by polyurea. The process described below is a general procedure for the preparation of polyurea microcapsules.

Deltamethrin is dissolved in a suitable solvent, preferably in Solvesso 200 (Aromatic solvent from ExxonMobil). To the solution polyisocyanates are added, selected from compounds that contain two or more isocyanate groups in the molecule. Preferred are di- and tri-isocyanates, examples are aliphatic diisocyanates and aromatic isocyanates like toluylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI, DESMODUR), polymethylenepolyphenylisocyanate (MONODUR, PAPI). The resulting oil phase is emulsified or dispersed in a water phase containing water soluble nonionic protective colloids, like PVA (polyvinylalcohols), PVP (polyvinylpyrrolidones), arabic gum, polyvinylmethylether, or others; and containing nonionic surfactants like EO/PO-fatty alcohols, EO/PO-linear alcohols, EO/PO-monobranch alcohols; and containing anionic dispersing agents like lignosulphonates, salts of lignosulphonates, salts of condensation products of naphthalenesulphonic acid, acrylic polymers, polymeric dispersants or others. By heating the mixture above room temperature, preferably to about 60°C, and/or adding a polyamine after the emulsification, the reaction takes place at the interphase and the capsule wall around the oil droplets is formed. Preferably, the polyurea is formed by heating the emulsified mixture.

Polyamines are compounds containing two or more amino groups in the molecule. These aminogroups are able to be bound to aliphatic or aromatic structures. The following amines are suitable for capsule wall formation: diethylentriamine, triethylentetraamine, hexamethylenediamine and triethylendiamine. Such amines can be used alone or in a mixture.

Preferably, the microcapsule shell wall has a thickness of between 1 and 100 nm, more preferably between 5 and 100 nm, more preferably between 5 and 50 nm, and more preferably between 10 and 30 nm. These ranges of shell wall thickness have been found to confer advantageous release properties for the insecticide, in that a dose which is toxic to ectoparasites may be released without achieving levels that are irritating or toxic to the animal.

Preferably, the microcapsule has a mean particle size of from 0.1 to 100 microns, as measured by laser diffraction. More preferably, the microcapsule has a mean particle size of from 0.2 to 5 microns, more preferably from 0.1 to 2 microns. This range of particle sizes has been found to be advantageous for use in the invention and may be varied according to the requirements of the particular system. For example, the ratio of surface area to enclosed volume will decrease as the particle size increases; accordingly, the release rate of the enclosed insecticide will be relatively higher in particles of a small size compared to the release rate in larger particles. This will mean that with smaller particles, more insecticide will be released, but over a shorter passage of time. Larger particles thus provide a slower release rate but over an extended period of time.

In one embodiment of the invention, the microencapsulated insecticide may include one or more additional active ingredients in addition to the insecticide, such as an anti-irritant, to reduce the irritating effects of the insecticide on the animal's skin. The anti-irritant may be incorporated in the core of the microcapsule or in a delivery system. Suitable anti-irritants will be well known to the skilled person. Examples of suitable anti-irritants include, for example, vitamin E, camomile, phytogenuous antiirritants, aloe vera, cola nitida extract, green tea extract, tea tree oil, liquorice extract, allantoin, urea, caffeine or other xanthines, glycyrrhizic acid and its derivatives, or triphenyl phosphate. The total concentration of antiirritant is preferably between 0.2 and 10 wt.%, more preferably between 1 and 2 wt.%.

In another embodiment of this invention, the microencapsulated insecticide may include an insect growth regulator. The insect growth regulator may be incorporated in the core of the microcapsule or in a delivery system. Suitable insect growth regulators will be well known to the skilled person and include, for example, Brevioxime, Buprofezin, Chlorfluazuron, Cyromazine, Diflubenzuron, Diofenolan, Farnesol, Fenoxycarb, Fluoromevalonate, Fluvastatin, Hexafumuron, Hydroprene, Imidazole, Indomethazine, Ketokonazole, Kinoprene, Methoprene, Mevinolin, Novaluron, Pyriproxyfen, Tebufenozide, Teflubenzuron, Triflumuron and Triprene. The total concentration of insect growth regulator is preferably between 0.01 and 3 wt.%, more preferably between 0.5 and 2 wt.%.

In another aspect of the present invention, there is provided a delivery system comprising a microencapsulated insecticide as described above. The delivery system comprises a microencapsulated insecticide and a suitable means for delivering the microencapsulated insecticide to the skin of an animal. Typical examples are listed, however the use of the microencapsulated insecticide is not limited to such systems.

In one embodiment, the delivery system comprises an aqueous or organic dispersion of the microencapsulated insecticide. By aqueous or organic dispersion, it is meant that an aqueous or organic medium forms a continuous phase in said delivery system. An aqueous dispersion of the microcapsule may be prepared directly by the interfacial oil-in-water polymerisation method described hereinabove. An organic dispersion of the microcapsule may be prepared directly by emulsifying the product of the interfacial oil-in-water polymerisation method described hereinabove in a continuous organic phase to generate an oil-in-water-in-oil emulsion. The aqueous or organic dispersion may be a lotion, gel, shampoo, spray-on or spot-on formulation, characterised by the fact that no significant release of the microencapsulated insecticide takes place prior to the application of such preparations. In a preferred embodiment of the invention, the delivery system comprises an organic dispersion of the microencapsulated insecticide. The organic dispersion of the microcapsule may be prepared directly by dispersing or emulsifying the product of the interfacial oil-in-water polymerisation method described hereinabove in a continuous organic phase to generate an oil-in-water-in-oil emulsion with good stability and running properties. A delivery system of this nature provides a double function:

1. The active ingredient is diluted homogenously to a level suitable for a spot-on application; and

2. The delivery system is self-running/spreading to provide an even distribution on the skin of the treated animal. A number of running oils are suitable for use in this delivery system, of which the following are preferred: Arlamol E (Propoxylated-15-stearyl alcohol), Estasan GT8-60 (medium chain triglycerides), Sunflower oil (long chain triglycerides), and Isopar V (isoparaffinic oil).

The delivery system of this aspect of the invention should also preferably include an emulsifier, of which the following are preferred examples: Atlox 4914, Atlox LP6, Atlox 4912, Span 20, Span 80, Brij 72, Brij 92V, Span 65, and Atlox LP6:LP1(1:4). The delivery system should contain between 1 and 30% microencapsulated insecticide, preferably, between 5 and 20%), more preferably around 10%>. The emulsifier component should be used at between 5 and 40%), preferably between 10 and 30%, more preferably at around 20%. The running oil should be used at between 50 and 95%, preferably between 60 and 80%, more preferably at around 70%. A preferred formulation for use with this aspect of the invention has the following composition:

Microencapsulated insecticide (Deltamethrin CS) 11.05%;

Emulsifiers 20.00;

Running oil 68.95. The preferred running oil for this application is Arlamol E and the best combination of emulsifiers is Span 65 10% and Atlox LP6:LP1(1 :4) 10%.

To prepare a delivery system according to this specific aspect of the invention, the following method can be used. First, to the running oil the emulsifiers are added under agitation. To produce a good homogeneous agitation use an agitator, such as an IKA agitator using a disperser in anchor form and at the speed of approximately 120rpm. Upon total solubilisation at room temperature the microencapsulated Deltamethrin suspension is added at the same agitation until a homogeneously inverted emulsion is produced.

In another embodiment, the delivery system comprises or is incorporated in a collar, brush, blanket or bed-lining characterised by the fact that no significant release of the microencapsulated insecticide takes place prior to the exposure of such preparations to the environment.

In another embodiment, the delivery system is a transdermal patch or implant, as described in WO98/00107, comprising the microencapsulated insecticide and characterised by the fact that no significant release of the microencapsulated insecticide takes place prior to the application of such preparations to the target.

The particular delivery system used will depend on the condition of the animal in need of treatment and the requirements of the animal owner. For example, if an animal is showing signs of serious infestation, then a curative treatment may be appropriate, in the form of a lotion, gel, shampoo, or spray-on formulation. Alternatively, if an animal appears to be free of infestation, then a preventative treatment will be more appropriate, such as a collar, brush, blanket or bed-lining impregnated with the microencapsulated insecticide.

The present invention is suitable for use on any type of animal, but is particularly suitable for use on domesticated or companion animals, that are highly susceptible to infestation by ectoparasites. Examples of domesticated animals include cows, pigs, sheep, goats, deer and horses. Companion animals are typically household pets, such as cats and dogs. The invention is particularly useful for the treatment of cats and dogs, for which infestation is a particular problem for pet-owners in view of the fact that these pets generally share the owner's dwelling. This means that infestation of carpets, soft furnishings clothes and even bedclothes may occur unless the pet is treated for ectoparasite infestation.

Various aspects and embodiments of the present invention will now be described in more detail by way of example, with particular reference to the following procedure, which has been optimised for the microencapsulation of deltamethrin. It will be appreciated that modification of details may be made without departing from the scope of the invention.

Figure 1 shows a typical particle size distribution for microcapsules according to the present invention.

Example 1

Microencapsulated deltamethrin was prepared by dissolving technical deltamethrin in Solvesso 200 to obtain 25% concentration.

Oil phase : in wt.% Deltamethrin concentrate 10

TDI (Toluenediisocyanate) 3

PAPI (Polyarylpolyphenylisocyanate) 2

Water phase: Pluronic L/64 (alkylphenol EO/PO) 0.5

Reax 100 (Sodiumlignosulphonate) 2

Dispersant (Sodium naphthalene sulphonate formaldehyde condensate) 1.5 Water to 100

The oil phase is maintained at a temperature of about 50°C prior to emulsification, but no longer than 6 hours. The water phase is kept at about 50°C prior to emulsification but not longer than 6 hours. The water phase is placed in a glass-jacketed reactor equipped with ultraturrax T25(IKA) stirrer fitted with a rotor tool suitable for emulsification. The oil phase is added into the water phase for oil in water emulsification. The speed of the ultraturrax is set at about 400 rpm. The speed is increased to about 10000 rpm and maintained for 3 minutes. Particle size is measured by laser diffraction (Malvern Mastersizer). If the particle size is in the range of 0.1 to 2 microns the emulsification step is considered satisfactory and the emulsion is maintained under agitation by an anchor stirrer at a speed of 90 to 120 rpm. The temperature is raised to 60°C and maintained for 2 hours. Thereafter the suspended microcapsules are cooled to room temperature and submitted to evaluation tests. The suspension of microcapsules is diluted to a concentration of 0.25 to 0.75% of deltamethrin in the selected medium for delivery.

Example 2

Example 1 was repeated with the exception that the oil phase contained 2 g of Vitamin E, which was added prior to emulsification.

Example 3

The method of Example 1 was repeated using the following ingredients

Oil phase : in wt.%

Deltamethrin concentrate (25%) in Solvesso 200 10

TDI (Toluenediisocyanate) 2.7

PAPI (Polyarylpolyphenylisocyanate) 1.6

Water phase:

Pluronic L/64 (alkylphenol EO/PO) 0.5

Reax 100 (Sodiumlignosulphonate) 2 Dispersant (Sodium naphthalene sulphonate formaldehyde condensate) 1.5

Vitamin E (entrapped in starch polymerised with Dextrin) 2

Water to 100

Example 4

The method of Example 1 was repeated using the following ingredients:

Oil phase : in wt.%

Deltamethrin concentrate (25%) in Solvesso 200 10 TDI (Toluenediisocyanate) 2.7

PAPI (Polyarylpolyphenylisocyanate) 1.6

Water phase:

Pluronic L/64 (alkylphenol EO/PO) 0.5 Reax 100 (Sodiumlignosulphonate) 2

Dispersant (Sodium naphthalene sulphonate formaldehyde condensate) 1.5

Phytogenuous Antiirritant (entrapped in starch polymerised with Dextrin) 2

Water to 100

Description of Test Procedures for the Microencapsulated Deltamethrin

1. Average Particle Size

The particle sizes of microencapsulated deltamethrin were determined by Laser diffraction using a Mastersizer (Malvern instruments). A typical particle size distribution for microcapsules according to the present invention is shown in Figure 1.

2. Shell Wall Thickness

Shell wall thickness was calculated using the oil fraction encapsulated, the percentage of monomer and polymer used in the encapsulation process, and the average particle size of the microcapsules. 3. Release Rate

Dispersions in water containing 0.05% active ingredient in the microencapsulated formulation of deltamethrin are placed into the donor compartment of a Permegear diffusion cell. The receptor compartment is filled with a mixture of water, diproylenglycol and surfactants at pH 5.5 and heated to 37°C. Samples are taken with a syringe every 2 hours, refilling the diffusion cell with water up to the mark. An aliquot sample is placed in a volumetric flask, filled with eluent to 25 ml. The active ingredient is extracted in an ultrasonic bath for 30 minutes. An aliquot is taken with a disposable syringe, filtered through a 0.2 μm nylon filter into an auto sampler vial and is submitted to HPLC analysis. The concentration of deltamethrin released is determined by reference to a known concentration standard.

4. Knock Down Activity

The efficacy of microencapsulated deltamethrin was evaluated in vitro in tests with Musca domestica (house fly). Dilutions of Examples 1 and 4 were prepared using deionised water, and regularly sprayed onto 0.1 m glass plates until the glass was completely wet. The glass plates were allowed to dry at room temperature and placed into transparent plastic bowls, covered with a lid. Each of the plastic bowls held 10 flies.

The time required to knock down 5 flies (KT50) and to knock down 9 flies (KT90) was recorded. When KT90 was reached, the treated glass plate was removed. Mortality was assessed after 24 hours.

An emulsion of non-encapusulated Permethrin was tested by the same method for comparison.

Results

Table 1 shows the particle sizes and shell wall thicknesses for Examples 1 -4

Table 1

Table 2 shows the release characteristics of Examples 1-4 in three repeated release measurements. Table 2

Table 2 (cont.)

The data show that release of deltamethrin from the microcapsules in all four Examples is substantially zero-order.

Table 3 shows the knock down activity of Examples 1 and 4 at varying concentrations. These were compared with two Permethrin formulations (Comparative Examples 1 and 2).

Comparative Example 1 was a water emulsion of Permethrin. Comparative Example 2 was a water emulsion of Permethrin, additionally containing 0.2% of a surfactant mixture of Tween 20 and Tween 85.

Table 3

Examples 1 and 4 showed excellent knock down activity against Musca domestica, even at low concentration. In each case, mortality after 24 hours was 100%. By contrast the non-encapsulated Permethrin showed inferior performance. Knock down activity for Permethrin was significantly worse than microencapsulated deltamethrin, even at a concentration of 250 ppm.

Thus, it has been shown in vitro that microencapsulated deltamethrin can deliver a dose of deltamethrin which is highly efficacious against insects, and at a dose which would not be toxic or cause irritation to a mammal when applied topically.

Example 5: A preferred delivery system has the following composition:

Microencapsulated insecticide (Deltamethrin CS) 11.05%;

Emulsifiers 20.00%;

Running oil 68.95%. The preferred running oil for this application is Arlamol E and the best combination of emulsifiers is Span 65 10% and Atlox LP6:LP1(1 :4) 10%.

The precise components of this candidate system are as follows:

Encapsulated oil phase Deltamethrin 0.5 Solvesso 200 2.57

BHT 0.03

Vitamin E acetate 0.17

Rimon growth reg. 0.06

Wall material 0.5

Catalysts 0.05

;r phase Surfactant 0.06

Protective colloids 2.32

Catalyst 0.03

Antifoam 0.01

Water/buffer pH 5.5 4.76 inuous oil phase Surfactants 20.00

Oil 68.95

It will, of course, be understood that the present invention has been described merely by way of example and that modifications of detail can be made within the scope of the invention.

Claims

1. A microencapsulated insecticide which is prepared by oil-in-water interfacial polymerisation, wherein said insecticide is a solid insecticide at room temperature and pressure and has limited solubility in organic solvents.

2. A microencapsulated insecticide according to claim 1 wherein the insecticide is selected from EPN, Methidathion, Chlorpyrifos, Phosalone, Dimethoate, Methamidophos, Fenpropathrin, Salithion, Fenoxycarb, Azinphos-Ethyl, Azinphos- Methyl, MTMC, Methomyl, Xylylcarb, Cloethocarb, Trichlorfon, Acephate, Amitraz, MIPC, Propoxur, Aminocarb, Aldicarb, , Fipronil, Imidacloprid, Acetamiprid, Thiamethoxam, Clothianidin, Dinotefuran, Nitenpyram, Trimethacarb, Dioxacarb,

Methiocarb, Bendiocarb, Vamidothion, Oxamyl, Hexythiazox, Acrinathrin, Allethrin, Alpha-Cypermethrin, Beta-cyfluthrin, Beta-cypermethrin, Bifenthrin, Bioallethrin, Bioallethrin S-cyclopentenyl isomer, Bioresmethrin, Cycloprothrin, Cyfluthrin, Cyhalothrin, Cypermethrin, Cyphenothrin[(lR)-trans.isomer] , Deltamethrin, Empenthrin [(EZ)-(lR)-isomer], Esbiothrin, Esfenvalerate, Fenpropathrin, Fenvalerate,

Flucythrinate, Flumethrin, Imiprothrin, Lamda-cyhalothrin, Permethrin, Phenothrin [(lR)-trans-isomer] , Prallethrin, Resmethrin, RU15525, Sumithrin, Tau- fluvalinate, Tefluthrin Tetramethrin, Tetramethrin[(lR)-isomer] , Theta-cypermethrin, Tralomethrin, Transfluthrin, Zeta-cypermethrin, ZXI8901, Etofenprox, Halfenprox and Silafluofen.

3. A microencapsulated insecticide according to claim 1 wherein the insecticide is deltamethrin.

4. A microencapsulated insecticide according to any one of the preceding claims, wherein the insecticide is microencapsulated by a polyurea shell wall.

5. A microencapsulated insecticide according to any one of the preceding claims, wherein the shell wall has a thickness from 5 to 100 nm.

6. A microencapsulated insecticide according to any one of the preceding claims, wherein the microcapsules have a mean particle size from 0.1 to 100 microns.

7. A microencapsulated insecticide according to any one of the preceding claims comprising at least one antiirritant.

8. A microencapsulated insecticide according to claim 7, wherein the at least one antiirritant is contained in the core of the microcapsule.

9. A microencapsulated insecticide according to claim 7 or 8, wherein the at least one antiirritant is selected from vitamin E or phytogenous antirritants.

10. A microencapsulated insecticide according to any one of the preceding claims comprising at least one insect growth regulator.

11. A microencapsulated insecticide according to claim 9 wherein the insect growth regulator is contained in the core of the microcapsule.

12. A microencapsulated insecticide according to claim 10 or 11 wherein the insect growth regulator is selected from Farnesol, Fenoxycarb, Fluoromevalonate, Fluvastatin,

Hexafumuron, Hydroprene, Imidazole, Indomethazine, Ketokonazole, Kinoprene, Methoprene, Mevinolin, Novaluron, Pyriproxyfen, Tebufenozide, Teflubenzuron, Triflumuron or Triprene.

13. A delivery system comprising a microencapsulated insecticide according to any of the preceding claims.

14. A delivery system according to claim 13 comprising an aqueous or organic dispersion of the microencapsulated insecticide.

15. A delivery system according to claim 14 wherein the dispersion is an aqueous dispersion.

16. A delivery system according to claim 14 wherein the dispersion is an organic dispersion.

17. A delivery system according to claim 16, which is prepared by emulsifying a microencapsulated insecticide according to any one of claims 1-12 in a continuous organic phase to generate an oil-in-water-in-oil emulsion.

18. A delivery system according to claim 17, which comprises a running oil and an emulsifier.

19. A delivery system according to claim 18, which comprises between 5 and 20%, more preferably around 10% microencapsulated insecticide, between 10 and 30% emulsifier, more preferably around 20%, and between 60 and 80% running oil, preferably around 70%.

20. A delivery system according to claim 19, wherein said microencapsulated insecticide comprises deltamethrin, the emulsifier component is a combination of Span 65 10% and Atlox LP6:LP1 (1 :4) and the running oil is Arlamol E.

21. A delivery system according to claim 15 wherein the aqueous dispersion comprises the microencapsulated insecticide in a concentration of 0.1 to 1 wt%.

22. A delivery system according to claim 21 wherein the concentration of microencapsulated insecticide is from 0.5 to 0.75 wt%.

23. A delivery system according to any one of claims 15 to 22 wherein the aqueous or organic dispersion further comprises an antiirritant.

24. A delivery system according to claim 23 wherein the antiirritant is as defined in claim 8.

25. A delivery system according to claim 23 or claim 24, wherein the antiirritant in the core of the microcapsule and/or the aqueous or organic dispersion has a total concentration of from 0.2 to 10 wt%.

26. A delivery system according to claim 25 wherein the total concentration of antiirritant is from 1 to 2 wt%.

27. A delivery system according to claim 15 to 26 wherein the aqueous or organic dispersion further comprises an insect growth regulator.

28. A delivery system according to claim 27 wherein the insect growth regulator is as defined in claim 12.

29. A delivery system according to claim 27 or 28 wherein the insect growth regulator in the core of the microcapsule and/or the aqueous dispersion has total a concentration of from 0.01 to 3 wt%.

30. A delivery system according to claim 29 wherein the total concentration of insect growth regulator is from 0.5 to 2 wt%.

31. A delivery system according to any one of claims 14 to 30 wherein the delivery system is a lotion, gel, shampoo, spray-on or spot-on formulation.

32. A delivery system according to claim 13, wherein the delivery system is a collar, comb, brush, blanket, bed-lining or other material incorporating or impregnated with the microencapsulated insecticide.

33. A composition in a delivery system according to claim 13, wherein the delivery system is a transdermal patch or implant comprising the microencapsulated insecticide.

34. A delivery system according to claim 33 wherein no significant release of the microencapsulated insecticide takes place prior to the application of the formulation.

35. A delivery system according to claim 33 wherein no significant release of the microencapsulated insecticide takes place prior to the exposure of the material to the environment.

36. A delivery system according to claim 33, wherein no significant release of the microencapsulated insecticide takes place prior to the application of the patch or implant to the target.

37. Use of a microencapsulated insecticide according to any of the claims 1 to 12 or a delivery system according to any of the claims 13 to 36 for the manufacture of a medicament for the treatment and/or prevention of infestation by ectoparasites in an animal.

38. Use according to claim 37 wherein the ectoparasite is a flea and/or a tick.

39. Use according to claim 37 or claim 38 wherein said animal is a domesticated or companion animal.

40. A method of treating and/or preventing infestation by ectoparasites in a mammal comprising administering to said mammal an effective amount of a microencapsulated insecticide according to any one of claims 1 to 12 or a delivery system according to any one of claims 13 to 36.