IE41449B1 - Control of animal parasites with benzimidazoles - Google Patents

Abstract

Parasiticidal compositions for controlling ectoparasites contain, as active ingredient, at least one compound of the following formula I where, in this formula, the substituents have the meanings given in Patent Claim 1. These compositions are administered to host animals which are infested with ectoparasites either orally or by injection or else with the aid of an implant. The active ingredient of the parasiticidal compositions according to the invention have a powerful insecticidal, acaricidal and nematicidal activity and is therefore suitable for controlling any ectoparasites from the class of the insects, mites and worms. The active ingredient of the formula I is prepared by reductive cyclisation of an acid amide of the formula III.

Description

ΙΤΑΤΕ OF INDIANA, UNITED STATES OF AMERICA, OF 307 EAST McCARTY STREET, :iTY OF INDIANAPOLIS, STATE OF INDIANA, UNITED STATES OF AMERICA. »2|p This invention relates to a further development of the invention described and claimed in Patent Specification No. /{&/%>.

In Patent Specification No. there is described and claimed a method of killing insect and acarina parasites which consume living tissues of a host animal which comprises orally Of percutaneously administering to the host animal a parasiticidally-effective amount of a compound of the formula (I) wherein R is chloro, trifluoroinethyl, difluoromothyL, or chlorodifluoromethyl; 3 Π 4 $ 5 R is hydrogen, -C-O-R , -C-R , —S-R3 S 0 0 II r -C-N(C1-C3 alkyl)2, -0-(0.^-0 alkyl), or -0-C-R5; R is chlorodifluoromethyl, trifluoromethyl, 1,1,2,2-tetrafluoroethyl, pentafluoroethyl, heptafluoropropyl, or heptafluoroisopropyl; R is C^-C^ alkyl, C2~C3 alkenyl, phenyl, or benzyl; R^ is C^-C^ alkyl, phenyl, chlorophenyl, anisyl, or tolyl; R^ is C^-C3 alkyl, or phenyl; or the ammonium, alkali metal, or alkaline earth metal salts of the compounds of formula (i) wherein R* is hydrogen.

The present invention is a modification of the invention described in the aforesaid application providing a similar method of killing insect and acarina parasites but with compounds of formula: wherein I< and R are defined as above. It will be observed that the only difference is the hydroxy at the 1-position. These compounds are useful as parasiticides.

The control of animal parasites is one of the oldest and most important problems of the animal husbandry industry. Parasites afflict virtually all species of animals. Most animals are afflicted by free-flying parasites such as flies, crawling ectoparasites such as lice and mites, burrowing parasites such as bots and grubs, and by microscopic endoparasites such as coccidia, as well as by larger endoparasites such as worms. Thus, the control of parasites even in a single host species is a complex and many-sided problem.

The insect and acarina parasites which consume living tissues of a host animal are particularly harmful. The group includes parasites of all economic animals, including ruminant and monogastric mammals and poultry, and of companion animals such as dogs as well. The term host animal as used heroin does not include humans.

Some progress has been made in the systemic control of some parasites, particularly those which burrow in or migrate through the host animal. Systemic control of animal parasites is accomplished by abserbing a parasiticide in the bloodstream or other tissues of the host animal. Parasites which eat or come into contact with the parasiticide-containing tissue are killed, either by ingestion or contact. A few phosphate, phophoramidate, ι and phosphorothioate insecticides and acaricides have been found to be sufficiently nontoxic to be used systemically in animals.

Recently, there has been much activity in the t field of benzimidazole chemistry. A great many patents and publications have appeared disclosing a variety of substituted benzimidazoles, some of which have insecticidal and acaricidal activity.

For example, Belgian Patent 766,870; Newbold et al., U.S. Patent 3,542,923; Patent Specification Nos. 29323 and 27690, and British Patent Specification No 1,144,620; French Patent 1,430,139; British Patent Specification No. l,113,999;South African Patent 69.02813; Holan et al., U.S. Patent 3,448.115; and Hannah et al.. U.S. Patent 3,749,734.

This invention provides a new method of killing by ingestion insect and acarina parasites which consume living tissues of a host animal which comprises orally or percutaneously administering to the host animal a parasiticidally-effective amount of a compound of the formula - 4 _ 4144 OH wherein R is chloro, trifluoromethyl, difluorometnyi, or chlorodifluoromethyl; and .

R is chlorodifluoromethyl, trifluoromethyl, 1,1,2,2-tetrafluoroethyl, pentafluoroethyl, heptafluoropropyl, or heptafluoroisopropyl.

A preferred group of compounds which are particu larly useful in this method have the formula £ •wherein R is chloro, fluoro, difluoromethyl, or trifluoromethyl; and -541449 g ....... . - ---.-R is chloro or trifluoromethyl, The following specific compounds are presented to assure that those skilled in the organic chemical and parasitological arts understand the scope of this invention. -chloro-l-hydroxy-7-nitro-2-trifluoromethylbenzimidazole 2-chlorodifluoromethyl-l-hydroxy-4-nitro-6trifluoromethylbenzimidazole 6- chloro-l-hydroxy-4-nitro-2-(1,1,2,2,-tetralO fluoroethyl) benzimidazole 7- difluoromethyl-l-hydroxy-5-nitro-2-pentafluoroethylbenzimidazole 6-chlorodifluoromethyl-2-heptafluoropropyl-lhydroxy-4-nitrobenzimidazole 2-heptafluoroisopropyl-l-hydroxy-6-nitro-5-trifluoromethylbenzimidazole The preferred compound of this invention is 1hydroxy-4-nitro-2-(l,1,2,2-tetrafluoroethyl)-6-trifluoromothylbenzimidazole.

The compounds of the invention are not novel and their method of preparation has therfore already been documented in the art. However, for the sake of completeness it may be mentioned that the 1 - hydroxybenzimidazoles of the invention can be prepared by reductive ring closure of an appropriately substituted acetanilide, which may, in turn, be prepared from an o - nitroaniline. - 6 41449 The procedure described below illustrates a typical synthesis useful in the preparation of compounds of' the invention. Organic chemists, guided by the above general teaching as well as the common skill of the chemical art, will be able to modify the procedure below to prepare all the benzimidazoles useful in the present invention.

Procedure A solution of 25.1 g. of 2,6-dinitro-4-trifluoromethylaniline in 100 ml. of pyridine was treated with trifiuoroacetyl chloride, which had been prepared from 10 ml. of trifluoroacetic acid. Ethanol was added to the resulting mixture until it was homogeneous, and the reaction mixture was then evaporated under vacuum. The residue after evaporation was washed with water, dried, dissolved in acetone, and filtered. Chloroform was added to the filtrate until the product precipitated. The precipitate was separated by filtration and dried to obtain the purified intermediate, 2’,6-dinitro~4’-trifluoromethyl-2,2,2trifluoroacetanilide.

A 1.75 g. portion of the above intermediate was dissolved in 100 ml. of ethyl acetate. One hundred mg. of 5 percent palladium on carbon was added, and the mixture was hydrogenated at an initial pressure of 13 psig. and room temperature until 0.01 mole of hydrogen had been taken up. The reaction mixture was then filtered and evaporated to dryness. The solid residue was taken up in about 300 ml. of ether, extracted into 5 percent Na^CO^, and acidified.

The desired l-hydroxy-4-nitro-2,6-bis(trifluoromethyl)benzimidazole precipitated and was separated by filtration. The product was then taken up in ether and dried over MgSO^, and - 7 41449 the ether was evaporated. The product was crystallized from chloroform to produce 900 mg. of l-hydroxy-4-nitro-2,6-bis(trifluoromethyl)benzimidazole, m.p. 222-224’C.

The ihstant method of parasite control is of the systemic type. The benzimidazole compounds described above have the ability to permeate the living tissues of a host animal to which one of the compounds is administered.

Insect and acarina parasites which consume blood or other living tissues of the host animal ingest the compounds with which the tissue is permeated, and are thereby killed. It is probable that the blood is the agency through which the compound is dispersed through the host animal, but parasites such as screwworms, which do not suck blood, are killed by this method, indicating that the compounds permeate other tissues as well as blood.

Some parasites, such as most ticks, feed on living tissues of the host animal during most of the parasite's life. Other parasites, such as screwworms, feed on the host only in the larval stage. A third group of parasites, such as the bloodsucking flies, feed on animal hosts only in the adult stage. Administration of the benzimidazoles of this method to host animals kills parasites which feed on the living tissues of the animals, no matter what the life stage, of the feeding parasite.

All the species of insect and acarina parasites which feed on the living tissues of animals are killed by this method. The parasites which suck the host animal's blood, those which burrow into and feed on the animal's tissue, and those, like the larvae of the bot flies, which enter a natural orifice of the host, attach to the -841440 mucous membranes, and feed therefrom are all equally effectively killed. For the sake of clarity, a number of specific parasites of various host animals which are controlled by this method will be mentioned. The parasitic life stage and the means by which it infests the host animal are given for each parasite.

Parasites of Horses horsefly, adult, bloodsucking stable fly, adult, bloodsucking black fly, adult, bloodsucking horse sucking louse, immature, adult, bloodsucking mange mite, nymph, adult, skin-burrowing scab mite, adult, skin-eating common horse bot fly, larva, migrating in alimentary canal chin fly, larva, migrating in alimentary canal nose bot fly, larva, migrating in alimentary canal Parasites of Bovines horn fly, adult, bloodsucking cattle biting louse, adult, skin-eating cattle bloodsucking louse, nymph, adult, bloodsucking tsetse fly, adult, bloodsucking stable fly, adult, bloodsucking horse fly, adult, bloodsucking cattle follicle mite, adult, skin-burrowing cattle tick, larva, nymph, adult, bloodsucking ear tick, nymph, bloodsucking Gulf Coast tick, adult, bloodsucking 41448 Rocky Mountain spotted-fever tick, adult, blood sucking lone-star tick, adult, bloodsucking heel fly, larva, migrating through the body bomb fly, larva, migrating through the body blowfly, larva, infesting wounds assassin bug, adult, bloodsucking Parasites of Swine hog louse, nymph, adult, bloodsucking chigoe flea, adult, bloodsucking Parasites of Sheep and Goats bloodsucking body louse, adult, bloodsucking bloodsucking foot louse, adult, bloodsucking sheep ked, adult, bloodsucking sheep scab mite, nymph, adult, skin-eating greenbottle fly, larva, infesting wounds black blowfly, larva, infesting wounds secondary screwworm, larva, infesting wounds Parasites of Poultry bed bug, nymph, adult, bloodsucking Southern chicken flea, adult, bloodsucking fowl tick, nymph, adult, bloodsucking chicken mite, nymph, adult, bloodsucking scaly-leg mite, adult, skin-burrowing depluming-mite, adult, skin-burrowing Parasites of Dogs horse fly, adult, bloodsucking stable fly, adult, bloodsucking mange mite, nymph, adult, skin-burrowing dog follicle mite, adult, burrowing in hair follicles -1041449 flea, adult, bloodsucking It will be understood that the parasites mentioned above are not confined to the single host animal with which each is here identified. Most parasites inhabit various hosts, although each parasite has a favorite host. For example, the mange mite attacks at least horses, hogs, mules, dogs, cats, foxes, rabbits, sheep, and cattle. Horseflies freely attack horses, mules, cattle, hogs, dogs, and most other animals. This method effectively kills parasites of the types described above growing in the host animals mentioned above, and in other host animals as well. For example, this invention is effective in cats, camels, and zoo animals.

The host animals in which this method is preferably practiced are dogs, bovines, sheep, or horses. The method is preferably used for the control of ticks, fleas, flies, or screwworms.

The time, manner, and rates at which the compounds of this method are effectively administered may be varied over a wide range. Detailed explanation of the ways in which this method is practiced will be given.

The compounds are administered to the animals at rates from 1 to 100 mg/kg. The best rate for killing a given parasite infesting a given animal must be determined individually, but it will be found that in most cases the optimum rate is within the preferred range of from 2.5 to 50 mg./kg. The optimum rate for a given instance depends on such factors as the health of the animal to be treated, the susceptibility of the parasite of primary concern, the expense which can be borne by the animal, -1141448 and the degree of control desired. Lower rates are safer for the host animal, less expensive, and often easier to administer, but are likely to give incomplete or minimum control of the parasite so that reinfestation may occur. On the other hand, higher rates of administration give more complete control of the parasites, but are more expensive and may impose a stress on the treated animals.

The compounds of this method are effective when administered at any time of year to animals of any age. It is possible to administer the compounds of this method to the animals continuously, as by constant feeding of a diet which contains one of the compounds, and thus assure that all parasites which contact the treated animals will be killed. Such administration is by no means economical, and it will usually be found best to administer the compoUhds at such times as to give the best return of parasite control for the compound expended. Certain parasites, such as cattle grubs, which are the larvae of the heel fly and the bomb fly, have a known active season when they attack animals. If such a parasite is of primary importance, this method can be practiced only during that season with assurance of year-round control of the parasite.

Other parasites, such as ticks, infest and bite animals essentially the year round. Control of such parasites can still be accomplished with relatively brief periods of administration by administering the compound to all the animals on a farm or in an area for a short period of time, such as for a few weeks. All the parasites of a generation are thus killed, and the animals can be ex30 pected to remain parasite-free fpr a considerable length -1241449 of time, until reinfested by parasites arriving with imported animals or the like.

The compounds of this method may be administered by any of the usual oral and percutaneous routes.

It should be noted that many of the compounds of this method are chemically changed by passage through the rumen of a ruminant animal. Oral administration to ruminant animals is therefore advisable only if the compounds are protected from the rumen environment by a special formulation. Such formulations will be discussed below.

The formulation and administration to animals of biologically-effective compounds is a very old and developed art. Some explanation of the different formulations and methods of administration will be given to j5 enable all to practice this method of parasite control.

Percutaneous administration of the benzimidazole compounds is carried out in the ways usual in the animal veterinary art. If a water-insoluble benzimidazole is desired, it is practical to dissolve the compound in a physiologically-acceptable solvent, such as the polyethylene glycols. It is likewise practical to formulate an injectable suspension of the benzimidazole as a fine powder, suspended in a formulation of physiologically-acceptable nonsolvents, surfactants, and suspending agents.

The nonsolvent can be, for example, a vegetable oil such as peanut oil, corn oil or sesame oil, a glycol such as a polyethylene glycol, depending on the benzimidazole chosen. -1341448 The compounds used in this invention are administered as compositions wherein the adjuvant employed is a substance other than water or common organic solvents. Suitable physiologically-acceptable adjuvants are necessary to keep the benzimidazole suspended. The adjuvants can be chosen from among the emulsifiers, such as salts of dodecylbenzene sulfate and toluenesulfonate, ethylene oxide adducts of alkylphenol, ahd oleate and laurate esters, and from the dispersing agents such as salts of naphthalenesulfonate, lignin sulfonate and fatty alcohol sulfates. Thickeners such as carboxymethyl cellulose» polyvinylpyrrolidone, gelatin and the alginates are also used as adjuvants for injectable suspensions. Many classes of surfactants, as well as those which have been discussed above, serve to suspend the benzimidazoles. For example, lecithin and the polyoxyethylene sorbitan esters are useful surfactants.

Percutaneous administration is conveniently accomplished by subcutaneous, intramuscular, and even intravenous injection of the injectable formulation. Conventional needle-type injection devices as well as needle-less airblast injection devices are useful.

It is possible to delay or sustain the permeation of the benzimidazole compound through the animal's living tissues by proper formulation. For example, a Very insoluble benzimidazole may be used. In that event, 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 benzimidazole can also be obtained by formulating the compound in a matrix which -1441449 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 well known in the art, are formulated in waxy semisolids such as vegetable waxes and high molecular weight polyethylene glycols.

Even more effective sustained action is obtained by introducing into the animal an implant containing one of the compounds. Such implants are now well known in veterinary medicine, and are usually made of a silicone-containing rubber. The benzimidazole compound is dispersed through a solid rubber implant or is contained inside a hollow implant. Care must be taken to choose a benzimidazole compound 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 the compound 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 benzimidazole compounds by means of an implant is a particularly preferred method of this invention. 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 tlia. -15compound for several months, and is easily inserted in the animal. No further handling of the animal or concern over the benzimidazole dosage is necessary after the insertion of the implant.

Oral administration of a benzimidazole may be performed by mixing the compound in the animal1s feed or drinking water, or by administering oral dosage forms such as drenches, tablets, or capsules.

When a compound of this method is to be administered orally to a ruminant animal, it is necessary to protect the compound from the deleterious effect of the rumen processes. The veterinary art is now aware of effective methods for coating and encapsulating compounds to protect them from the rumen. For example, coating materials and methods are disclosed in Grant et al., D.S. Patent 3,697,640. Grant teaches a method of protecting substances from action of cellulose propionate 3-morpholinobutyrate. Such a film can be used to protect the benzimidazoles of this method. Conveniently, tablets, or capsules containing a benzimidazole are coated with the film in a coating pan or a fluidized bed spray apparatus. Pellets of the parasiticide may be made, coated with the film, and filled into capsules. Alternatively, a solid mixture of the benzimidazole and the film-forming agent may be made and broken or ground into small particles, each of which comprises the benzimidazole enclosed in a matrix of the film-forming agent. The particles may be filled into capsules for oral administration, or made into an oral suspension. -1641449 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 benzimidazole is dispersed in a liquid or particulate solid carrier. The premix may conveniently contain from about 1 to about 400 g. of compound per pound, depending on the desired concentration in the feed. As the art is aware, many benzimidazoles will be hydrolyzed or degraded by constituents of animal feed. Such compounds are routinely formulated in protective matrices such as gelatin before addition to the premix. The premix is in turn formulated into feed by dispersing it in the feed mixture in a conventional mixer. The correct amount of benzimidazole, and hence of premix, to mix in the feed is easily computed by taking into account the weight of the animals, the approximate amount each animal eats per day, and the concentration of the benzimidazole in the premix.

The compounds can easily be formulated into tablets and capsules according to the conventional methods, about which no teaching is required here. Drench formulations comprise the benzimidazole compound dissolved or dispersed in an aqueous liquid mixture.

The following example reports representative results of a bio-assay test. -1741449 Example Larvae of the black blowfly were used as assay organisms in a bio-assay test system. The tests were carried out by administering a compound of formula I as a single subcutaneous injection to a calf. Samples of blood were withdrawn from the calf on successive days after the administration of the compound, and blowfly larvae were fed on the withdrawn whole blood. The end point of the test was recorded as the last day on which 90 percent or more of the blowfly larvae were killed.

Aqueous suspensions of l-hydroxy-4-nitro-2(1,1,2,2-tetrafluoroethyl)-6-trifluoromethylbenzimidazole were administered at rates of 5, 10 and 15 mg./kg. The 15 mg./kg. rate killed 90 percent or more of the larvae for four successive days, and administration at 10 mg./kg. killed the larvae for three days. The 5 mg./kg. rate was not effective.

In the tests of this example, the parasites were exposed to the treated animal's blood indirectly,. instead of directly by feeding the parasites on the animal. The control obtained, however, is obviously as significant as if the parasites had sucked blood directly from the animal. The value of the method in protecting animals from the very injurious parasite, the blowfly, is clearly demon25 strated by the tests, si-ice several days of parasite control were obtained from a single administration of a compound of this invention.

Claims (12)

1. CLAIMS:1. A method of killing insect and acarina parasites which consume living tissues of a host animal which comprises orally or percutaneously administering to the host animal a parasiticidally-effective amount of a compound of the formula wherein R is chloro, trifluoromethyl, difluoromethyl, or chlorodifluoromethyl; and R 2 is chlorodifluoromethyl, trifluoromethyl, 1,1,2,2-tetrafluoroethyl, pentafluoroethyl, heptafluoropropyl, or heptafluoroisopropyl.

2. A method of killing insect and acarina parasites which consume living tissues of a host animal which comprises orally or percutaneously administering to the host animal a parasiticidally-effective amount of a compound of the formula -1941440 OH X I Χγ\ (III) θ wherein R is chloro, fluoro, difluoromethyl, or trifluoromethyl; and R is chloro or trifluoromethyl. 5

3. The method of Claim 1 in which the compound of formula (II) is l-hydroxy-4-nitro-2-(l,l,2,2-tetrafluoroethyl)-6-trifluoromethylbenzimidazole.

4. The method of Claim 1, 2 or 3 in which from 1 mg./kg. to 100 mg./kg. of the compound is administered to the 10 host animal.

5. The method of Claim 4 in which from 2.5 mg./kg. to 5θ mg./kg. of -che compound is administered to the host animal.

6. The method of Claim 4 or 5 in which the admini15 stration is percutaneous.

7. The method of Claim 4 or 5 in which the compound is administered in an implant.

8. A parasiticidal composition for oral or percutaneous administration to an infected host animal 20 which comprises an.adjuvant as hereinbefore defined and as active ingredient a compound of the formula -2041449 wherein R and R are defined as in Claim 1

9. A parasiticidal composition for oral or percutaneous administration to an infected host animal which comprises an adjuvant as hereinbefore defined and as active ingredient a compound of the formula

10. The composition of Claim 8 in which the compound of formula (II) is l-hydroxy-4-nitro-2-(1,1,2,2tetrafluoroethyl)-6-trifluoromethylbenzimidazole.

11. The composition of Claim 8, 9 or 10 adapted for percutaneous administration,

12. A composition according to any one of Claims 8 to 10, in tho form of an inplant.