Method of Preventing the Reinfestation of Dogs and Cats by Fleas

Surprisingly, it has been found that by specific modes of application and by using active ingredients which block the development of juvenile flea stages, the vicious circle of constantly recurring reinfestation, described above in detail, can be brought to an end in simple manner, thereby preventing the fleas from reproducing and, in addition, keeping the habitat of dogs and cats permanently free from fleas.

It has been found that by administering to dogs or cats orally or parenterally or by implant a larvicidally or ovicidally effective amount of a flea growth inhibiting substance, the reinfestation of dogs and cats by fleas can be drastically reduced or completely prevented.

It has further been found that in particular the following three classes of active ingredients are suitable for such use:

(a) a juvenile hormone or juvenile hormone-like chemical,

(b) a flea growth inhibiting benzoylurea derivative, or

(c) a flea growth inhibiting triazine derivative.

It is known that some representatives of the substance classes (a), (b) and (c) inhibit or completely suppress the further development of juvenile stages; however, this activity has always been observed when the active ingredient is applied direct to the parasites. In connection with the present invention, it is surprising, however, that the full activity is still achieved even when the active ingredient is administered to the host animal in relatively low concentrations and it reaches, in an indirect way, the adult flea via the blood ingested and, additionally, the flea larvae (the actual target) when they feed upon the faeces excreted by the adults. By killing merely the adult fleas, which has so far been the objective of methods of control, the host animal is freed from fleas for a short time only. It has been found that fleas can only be effectively controlled if the development of new flea populations from the flea eggs is successfully prevented.

Target pests may be exposed to compounds in two ways. Chemicals are ingested in the blood meal by adult insects and pass from adults to the egg where they are effective. Death may occur at the egg, larval or pupal stage. Research on fleas indicates reduced egg production, high larval mortality and inability of adults to eclose from the pupal case. In addition to transmission to the egg, larval fleas are exposed when they feed upon faeces excreted by adult fleas. Flea faeces contain large amounts of undigested blood taken from the host and serve as a protein source for the developing flea.

Accordingly, the present invention embraces two aspects; namely the above-described method of preventing dogs and cats from being reinfested by fleas, and, at the same time, the suppression of the propagation of fleas, or to put it more precisely:

A method of preventing the propagation of fleas, comprising the step of providing the fleas with nutrient blood which contain an effective amount of at least one of the active ingredients as identified above. This method also includes the aspect that the nutrient blood is provided to the fleas by feeding an effective amount of one of said active ingredients to a host dog or a host cat and letting the fleas feed thereon.

All three substance classes (a), (b) und (c) and the preparation thereof are described in the literature. Juvenile hormones or juvenile hormone-like chemicals [class (a)] are described in the following publications: Chemie der Pflanzenschutz- und Schadlingsbekampfungsmittel (The Chemistry of Plant Protectants and Pesticides), R. Wegler, Springer-Verlag Berlin, Heidelberg, New York 1981, Vol. 6, pp. 185 to 214.

Insecticide Mode of Action, Joel R. Coats, Academic Press (1982) pp. 315 to 402.

U.S. Pat. Nos. 4,172,146; 3,987,102; 3,987,108; 3,988,477; 4,007,280; 4,100,296; 4,097,581; 4,060,629; 4,080,470; EP No. 4,334; UK No. 2,084,574; EP Nos. 169,169; 72,475; U.S. Pat. Nos. 4,092,365; 4,057,587; 4,017,549; DE-OS No. 2,528,345; EP No. 37,092; U.S. Pat. No. 4,061,683; DE-OS No. 2,925,113; Chem. Abstr., Vol. 102, p 668, 113025e; Chem.Abstr., Vol. 102, p. 222, 57842e; Chem.Abstr., Vol. 102, p. 569, 61919c; UK No. 2,102,425, and Agric.Biol.Chem., Vol. 49, pp. 3197 to 3202 (1985).

Representative examples of particularly preferred substances of class (a) are the following compounds:

Class (b): Flea growth inhibiting benzoylurea derivatives, which are also known to the skilled person under the name of "dimiloids", are described e.g. in DE-OS Nos. 2,123,236; 2,601,780; 3,240,975; EP Nos. 72,438, 42,533 and especially EP No. 79,311.

Preferred compounds of class (b) for being employed in the method of the present invention are the following compounds of the formula I ##STR27## wherein

R.sub.1 is hydrogen, halogen or methyl; and

R.sub.2 is hydrogen or halogen.

A preferred subgroup within the compounds of the formula I consists of those representatives, wherein

R.sub.1 is hydrogen, fluorine, chlorine or bromine; and

R.sub.2 is hydrogen, fluorine, chlorine or bromine.

Most preferred are those representatives of the formula I, wherein

R.sub.1 is 4-fluorine, 4-chlorine, 4-bromine or 4-methyl; and

R.sub.2 is chlorine.

Representative examples of particularly preferred individual compounds of class (b) are:

Class (c): Flea growth inhibiting triazine derivatives which can be employed in the method of this invention are described e.g. in U.S. Pat. Nos. 4,225,598; 4,160,831; 4,160,832; 4,187,304; 4,187,305 and DE-OS No. 3,030,646.

The following group of compounds of this class (c) is to be singled out as being particularly suitable: ##STR28## wherein

R.sub.a is cyclopropyl or isopropyl;

R.sub.b is hydrogen, halogen, C.sub.1 -C.sub.12 alkylcarbonyl, cyclopropylcarbonyl, C.sub.1 -C.sub.12 alkylcarbamoyl, C.sub.1 -C.sub.12 alkylthiocarbamoyl or C.sub.2 -C.sub.6 alkenylcarbamoyl; and

R.sub.c is hydrogen, C.sub.1 -C.sub.12 alkyl, cyclopropyl, C.sub.2 -C.sub.6 alkenyl, C.sub.1 -C.sub.12 alkylcarbonyl, cyclopropylcarbonyl, C.sub.1 -C.sub.12 alkylcarbamoyl, C.sub.1 -C.sub.12 alkylthiocarbamoyl or C.sub.2 -C.sub.6 alkenylcarbamoyl, and the acid addition salts thereof which are non-toxic for warm-blooded animals.

The following Table 3 shows typical representatives of compound of formula X.

Compound 3.1, cyromazine is particularly preferred.

It is an essential feature of the present invention that the active ingredient selected from the above-mentioned substance classes (a), (b) and (c) is administered in such a manner that it can be ingested by the adult sucking flea with the blood of the host animal and can then exhibit activity the juvenile flea stages. In accordance with the present invention, this is achieved with several forms of application, e.g. by administering a formulated active ingredient orally. In this case, the term "formulated" means e.g. in the form of a powder, a tablet, a granulate, a capsule, an emulsion, a foam, etc. The preparation does not necessarily have to be administered to the animal direct; it may be convenient to mix it with the animal's feed. In addition to containing adjuvants conventionally employed in the art of formulation, the compositions to be administered orally may of course contain further additives which stimulate voluntary ingestion by the animal, e.g. suitable scents or flavourings. Owing to its simplicity, oral application is one of the preferred objects of the present invention. A further mode of application is parenteral application, e.g. by subcutaneous, intravenous or intramuscular injection or by means of a sustained action preparation in the form of an implant or other depot formulation.

Methods of oral application include but are not limited to compounds premixed in dog and cat food, fed in biscuits or treats, chewable tablets, water-dissolvable capsules or tablets, water-soluble compounds applied with a dropper into water or materials applied in any form onto dog food. Implants include any device applied into the animal for release of compounds to control fleas.

Percutaneous administration is conveniently accomplished by subcutaneous, dermal, intramuscular and even intravenous application of the injectable formulation. Conventional needle-type injection devices as well as needle-less air-blast injection devices and pour-on and spot-on formulations may be useful.

It is possible to delay or sustain the permeation of the active ingredient through the animal's living tissues by proper formulation. For example, a very insoluble compound may be used. In this case, the slight solubility of the compound causes sustained action because the body fluids of the animal can dissolve only a small amount of the compound at any one time.

Sustained action of the active ingredient can also be obtained by formulating the compound in a matrix which will physically inhibit dissolution. The formulated matrix is injected into the body where it remains as a depot from which the compound slowly dissolves.

Matrix formulations, now known in the art, are formulated in waxy semisolids such as vegetable waxes and high molecular weight polyethylene glycols.

Very effective sustained action is obtained by introducing into the animal an implant containing one of the active ingredients. Such implants are now well known in veterinary art and are usually made of a silicone-containing rubber. The active ingredient is dispersed through a solid rubber implant or is contained inside a hollow implant. Care must be taken to choose an active ingredient which is soluble in the rubber from which the implant is made, since it is dispersed by first dissolving in the rubber and then leaching out of the rubber into the body fluids of the treated animal.

The rate at which active ingredient is released from an implant, and hence the length of time during which the implant remains effective, is controlled with good accuracy by the proper adjustment of the concentration of the compound in the implant, the external area of the implant, and the formulation of the polymer from which the implant is made.

Administration of the active ingredient by means of an implant is a further particularly preferred embodiment. Such administration is highly economical and efficacious because a properly designed implant maintains a constant concentration of the compound in the tissues of the host animal. An implant can be designed to supply compound for several months and is easily inserted in the animal. No further handling of the animal or concern over the dosage is necessary after the insertion of the implant.

The formulation of veterinary additives in animal feed is an extremely well-known art. It is usual to formulate the compound first as a premix in which the active ingredient is dispersed in a liquid or particulate solid carrier. The premix may conveniently contain from about 1 to 800 g of compound per kilogram, depending on the desired concentration in the feed. As is known in the art, many active ingredients can be hydrolysed or degraded by constituents of animal feed. Such compounds are routinely formulated in protective matrices such as gelatin before addition to the premix.

Therefore, the present invention is also directed to a method of systemically preventing the reinfestation of dogs and cats by fleas, which method comprises administering to said host animals orally, parenterally or by implant a larvicidally or ovicidally effective amount of a flea growth inhibiting substance, and especially to a method, wherein the active ingredient is selected from the group consisting of

(a) a juvenile hormone or a juvenile hormone-like chemical,

(b) a flea growth inhibiting benzoylurea derivative,

and

(c) a flea growth regulating triazine derivative.

The present invention also relates to a method of preventing the propagation of fleas, comprising the step of providing the fleas with nutrient blood which contains an effective amount of a flea growth inhibiting substance selected from the three classes of active ingredients as described above or more specifically the present invention also relates to the method of preventing the propagation of fleas by feeding an effective amount of a flea growth inhibiting substance, as characterized above, to the host animal and letting the fleas feed thereon.

Within the scope of this invention, a juvenile hormone-like chemical will be understood as meaning a chemical which acts like a juvenile hormone.

The active ingredient is selected from one of the classes (a), (b) or (c) is conveniently applied in a dose of 0.01 to 800, preferably 0.5 to 200, most preferably 1 to 30, mg/kg body weight, based on the host animal, with oral administration being preferred.

A good dose for regular administration is in general in the range from 1 to 100 mg/kg body weight of the host animal. Doses are usefully regularly repeated at daily to weekly intervals.

The total dose of a particular active ingredient may vary from one genus of animal to the other and may even vary within the same genus since said dose depends, inter alia, on the weight and constitution of the animal.

In the method of the present invention, the active ingredient is not normally applied in pure form, but preferably in the form of a composition which, in addition to containing the active ingredient, contains application promoters which are tolerated by the host animal. Naturally, in addition to the method of controlling juvenile development stages in accordance with the present invention, the adult fleas may also be controlled by conventional methods. However, these additional measures are not absolutely necessary.

The composition to be applied in the method of this invention usually contain 0.1 to 99% by weight, preferably 0.1 to 95% by weight, of active ingredient selected from one of the classes (a), (b) or (c), and 99.9 to 1% by weight, preferably 0.1 to 25% by weight, of a solid or liquid non-toxic adjuvant, including 0 to 25% by weight, preferably 0.1 to 25% by weight, of a non-toxic surfactant.

Whereas commercial products are preferably formulated as concentrates, the end user will normally employ dilute formulations.

The compositions may also contain further ingredients, such as stabilisers, antifoams, viscosity regulators, binders, tackifiers as well as other active ingredients for obtaining special effects. Materials known from veterinary practice as being suitable for being administered orally, parenterally or by implant may be employed as formulation assistants. A number of examples are cited below.

Suitable carriers are especially fillers, such as sugars, for example lactose, saccharose, mannitol or sorbitol, cellulose preparations and/or calcium phosphates, for example tricalcium phosphate or calcium hydrogen phosphate, also binders, such as starch pastes using, for example, corn, wheat, rice or potato starch, gelatine, tragacanth, methylcellulose and/or, if desired, disintegrators, such as the above-mentioned starches, also carboxymethyl starch, cross-linked polyvinylpyrrolidone, agar, alginic acid or a salt thereof, such as sodium alginate. Adjuncts are especially flow-regulating agents and lubricants, for example silica, talc, stearic acid or salts thereof, such as magnesium stearate or calcium stearate, and/or polyethylene glycol. Dragee cores can be provided with suitable coatings that may be resistant to gastric juices, e.g. concentrated sugar solutions which may contain gum arabic, talc, polyvinylpyrrolidone, polyethylene glycol and/or titanium dioxide, or lacquer in suitable organic solvents or solvent mixtures or, for the production of coatings that are resistant to gastric juices, solutions of suitable cellulose preparations, such as acetylcellulose phthalate or hydroxypropylmethylcellulose phthalate. Colourings, flavourings or pigments can be added to the tablets or dragee coatings, for example for identification purposes or to indicate different doses of active ingredient.

Further orally administrable preparations are dry-filled capsules consisting of gelatine and also soft, sealed capsules consisting of gelatine and a plasticiser, such as glycerol or sorbitol. The dry-filled capsules may contain the active ingredient in the form of a granulate, for example in admixture with fillers, such as lactose, binders, such as starches, and/or glidants, such as talc or magnesium stearate, and optionally stabilisers. In soft capsules, the active ingredient is preferably dissolved or suspended in suitable liquids, such as fatty oils, paraffin oil or liquid polyethylene glycols, it being possible also to add stabilisers. Preferred are, inter alia, capsules that can be easily bitten through or swallowed without being chewed.

Especially suitable for parenteral administration are aqueous solutions of an active ingredient in water-soluble form, for example a water-soluble salt, also suspensions of the active ingredient, such as corresponding oily injection suspensions, e.g. suitable lipophilic solvents or vehicles, such as fatty oils, for example sesame oil, or synthetic fatty acid esters, for example ethyl oleate, or triglycerides, or aqueous injection suspensions that contain viscosity-increasing substances, for example sodium carboxymethylcellulose, sorbitol and/or dextran, and, optionally, also stabilisers.

The preparations of the present invention can be manufactured in a manner known per se, for example by means of conventional mixing, granulating, confectioning, dissolving or lyophilising processes. For example, pharmaceutical preparations for oral administration can be obtained by combining the active ingredient with solid carriers, optionally granulating a resultant mixture, and processing the mixture or granulate, if desired or necessary after the addition of suitable adjuncts, to form tablets or dragee cores.

The following Examples illustrate the invention described hereinbefore, but do not limit its scope in any way.

Tablets containing 25 mg of active ingredient, for example 2-cyclopropylamino-4,6-bis(dimethylamino)-s-triazine, can be manufactured as follows:

All the solid ingredients are first forced through a sieve having a mesh width of 0.6 mm. Then the active ingredient, the lactose, the talc, the magnesium stearate and half of the starch are mixed. The other half of the starch is suspended in 40 ml of water and this suspension is added to a boiling solution of the polyethylene glycol in 100 ml of water. The resulting starch paste is added to the main batch and the mixture, if necessary with the addition of water, is granulated. The granulate is dried overnight at 35.degree. C., forced through a sieve having a mesh width of 1.2 mm and pressed to form tablets having a diameter of approximately 6 mm that are concave on both sides.

Tablets containing 0.02 g of active ingredient, for example are 2-cyclopropylamino-4,6-bis(dimethylamino)-s-triazine, are manufactured as follows:

A mixture of the active ingredient, the lactose and 194.70 g of the potato starch is moistened with an ethanolic solution of the stearic acid and granulated through a sieve. After drying, the remainder of the potato starch, the talc, the magnesium stearate and the colloidal silica are admixed and the mixture is pressed to form 0.1 g tablets which, if desired, can be provided with breaking grooves for finer adjustment of the dosage.

Capsules containing 0.025 g of the active ingredient, for example 2-cyclopropylamino-4,6-bis(dimethylamino)-s-triazine, can be manufactured as follows:

The active ingredient is mixed with the lactose and the mixture is moistened uniformly with an aqueous solution of the gelatine and granulated through a sieve having a mesh width of 1.2-1.5 mm. The granulate is mixed with the dried corn starch and the talc and introduced in portions of 300 mg into hard gelatine capsules (size 1).

0.25 parts by weight of active ingredient and

4.75 parts of secondary calcium phosphate, or China clay, aerosil or carbonate or lime are homogeneously mixed with

95 parts of an animal feed.

8 parts by weight active ingredient

3.6 parts of acetic acid

88.4 parts of water for injection

The acetic acid and the water are added to the active ingredient and the mixture is stirred until everything has dissolved. The solution is then filtered and sterilised by a suitable method. pH of the solution: 5.0.

20 parts of active ingredient are mixed with

20 parts of emulsifier, e.g. a mixture of alkylarylpolyglycol ether with alkylarylsulphonates, and

60 parts of solvent until the solution is completely homogeneous. By diluting this concentrate with water it is possible to obtain an emulsion of the desired concentration.

15% active ingredient in 2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane

10% active ingredient in diethylene glycol monoethyl ether

10% active ingredient in polyethylene glycol (mol. wt. 300)

5% active ingredient in glycerol

25 parts of active ingredient

1 part of sodium lauryl sulfate

3 parts of colloidal silica

71 parts of urea

The constituents are mixed and the mixture is finely ground in a suitable mill.

Other biocidal active ingredients or agents which are inert towards the active ingredients and acceptable to the animals to be treated, or mineral salts or vitamins can be admixed to the compositions described.

In a manner analogous to that described in the formulation Examples 1 to 8, it is possible to manufacture corresponding preparations containing a compound of the classes (a), (b) or (c) as defined above.

Dogs with a proven ability to maintain flea infestations were infested with 100 cat fleas (Ctenocephalides felis (Bouche)). Animals were then divided into 3 groups of two (See Table A). The dogs from two groups were then treated orally with the active ingredient for 10 consecutive days at a dose rate of either 3 or 5 mg/kg body weight/day (Table A). The active ingredient was administered (via a syringe) as suspension formulation dissolved in water. The third group of two animals served as non-treated controls.

3, 8 and 10 days after the start of treatment flea eggs were collected on paper placed under boxes in which the dogs were kept overnight. The eggs were counted, placed on a larval rearing medium and incubated. The number of pupae and adult fleas which hatched was determined (Table B).

The data show that by 3 days after the start of treatment with 5 mg active ingredient kg/day no adult fleas developed from the eggs of fleas which fed on these treated dogs.

These findings show that when adult female fleas take a blood meal from dogs dosed with 5 mg/kg/day, all eggs which are laid by these fleas fail to develop into adult fleas. In this manner the life cycle of the flea is broken and flea control is achieved.