Therapeutics: parasiticide

Endoparasiticides

Nematodes

• Toxocara canis : benzimidazoles more effective than piperazine against larval stages therefore prevent fecal output for longer period; pregnant/nursing bitches need daily treatment with fenbendazole to prevent larval migration across placenta and into milk.
• Toxascaris , Uncinaria , Ancylostoma caninum and Trichuris : treat adults every few months; monthly from late pregnancy until weaning. Pups should be treated at age 2 weeks, 4 weeks, 8 weeks and 6 months, or if transmission very likely, age 2 weeks, 4 weeks, 6 weeks, 8 weeks, 6 months.
• Angiostrongylus usually responds to levamisole , but fenbendazole may be safer though less effective; Oslerus( Filaroides) needs repeated treatment with albendazole* or fenbendazole .
• Heartworm: Dirofiliaria immitis treat with melarsomine * for prophylaxis use monthly ivermectin , selamectin , moxidectin (unlicensed use in dogs) or milbemycin oxime .
• Nasal worms: Eucoleus (Capillaria) Boehmi treat with ivermectin.

Drugs for nematodes Avermectins and milbemycins

• Ivermectin * - used to control migrating heartworm larvae.
  Approved in US only as a preventative for heartworm.
  Toxicity in Collies/Collie-x; seen at the higher doses used to treat ectoparasites, not at heartworm preventative dosees (dose difference - 6 ug/kg for heartworm; 200 ug/kg to treat ectoparasites).
• Natural or semi-natural macrocyclic lactone fermentation products of Streptomyces spp that induce neuromuscular paralysis in susceptible parasites by binding to and opening glutamate-gated chloride channels (glutamate agonists).
• Effective against wide range of nematodes.
• Also termed endectocides because also active against many ectoparasites.
• Kill existing population of parasites and prevent re-infection for a period of time.
• Selamectin : prevention of heartworm disease caused by D. immitis.
• Milbemycin oxime .

Benzimidazoles

• Disrupt parasite energy metabolism by binding to tubulin (required for uptake of nutrients).
• Doses may need to be repeated in dogs.
• Effective against larval and adult roundworms, some also ovicidal.
• Products containing benzimidazoles or probenzimidazoles are labelled 1-BZ.
• Albendazole : lungworm - Oslerus (formerly known as Filaroides) .
  Teratogenic in early pregnancy.
• Fenbendazole : for pregnant and lactating bitches to prevent roundworm in puppies, also for hookworms, whipworms, lungworm and tapeworm ( Taenia - not licensed for Echinococcus or Dipylidium). Needs daily treatment from day 40 of pregnancy through to 2 days post-partum to achieve this.
• Mebendazole : gastrointestinal roundworms, Echinococcus and Taenia . Need to treat longer if treating tapeworms.
• Praziquantel : preferred treatment for Echinococcus .
• Febantel .

Imidazothiazoles

• Nicotinic receptor agonists interfere with parasite nerve transmission → muscular paralysis and expulsion.
• Restores depressed T-cell function.
  Low therapeutic index - toxic signs include salivation and muscle tremors.
• Levamisole hydrochloride * : lungworms ( Angiostrongylus ), immune stimulation, heartworm treatment (seek specialist advice).

Organophosphorous compounds

• Dichlorvos : roundworms, hookworms. Not recommended. Safer drugs are available.

Tetrahydropyrimidines

• Interfere with parasite nerve transmission → neuromuscular paralysis.
• Effective against adults and larval gastrointestinal roundworms and hookworms.
• Pyrantel embonate , pyrantel pamoate, pyrantel tartrate : (not licensed for use in cats).

Others

• Nitroscanate : roundworms and tapeworms (at recommended dose it gives only limited control of echinococcus).
• Piperazine : modifies neurotransmission → relaxation and expulsion; for some roundworms, ie Toxocara, Toxascaris and Uncinaria; little activity against larval Toxocara in puppies; ineffective against lungworms or tapeworms.
• Diethylcarbamazine : piperazine derivative that acts in nicotine-like manner causing paralysis. Used for heartworm prophylaxis and has ascaricide activity. Has been used to treat Spirocerea lupi at very high doses.

Tapeworms

• All tapeworms have an indirect lifecycle and control measures should, where possible, include control of intermediate hosts, eg Dipylidium - flea control.
• Dipylidium , Echinococcus (zoonotic), Taenia Diphyllobothrium latum and Spirometra mausonoides affect dogs.

Drugs for tapeworms

Some benzimidazoles have activity against tapeworms; nitroscanate is also effective.

• Dichlorophen : effective against Dipylidium and Taenia.
• Praziquantel : tapeworms (drug of choice for Echinococcus). Mechanism of action; impairs integument function enhancing permeability to glucose leading to nutrient loss.
• Epsiprantel : same spectrum of activity and treatment efficacy as praziquantel.
• Fenbendazole : effective against Taenia spp.

Compound endoparasiticides

• For multiple parasitism → broad spectrum roundworm and tapeworm control, eg febantel and praziquantel.

Flukes/trematodes

• Nanophyetus salmincola acquired by consumption of raw trout or salmon in North West US.
• Paragonimus kellicotti acquired by consumption of raw crayfish or freshwater crab.
• Drugs for Trematodes:
  • P. kellicotti - praziquantel 23 mg/kg TID for 3 d (Bowman et al1991), fenbendazole 50 mg/kg for 10-14 d (Dubey et al1979), albendazole 25 mg/kg BID for 14 d.
  • N. salmincola - praziquantel 7-38 mg SQ or IM (Foreyt & Gorham, 1988).

Sources

Publications

Refereed papers

• Recent references from PubMed.
• Mealey K L (2008) Canine ABCB1 and macrocyclic lactones: heartworm prevention and pharmacogenetics. Vet Parasitol 158 (3), 215-222 PubMed.
• Estrada-Peria A & Ascher F (1999) Comparison of an amitraz-impregnated collar with topical administration of fibronil for prevention of experimental and natural infestations by the brown dog tick (Rhipicephalus sanguineus). JAVMA 214 (12), 1799-1803.
• Marsella R (1999) Advances in flea control. Vet Clin North Am Small Anim Pract 29 (6), 1407-1424.
• Paiement J P, Leger C, Ribeiro P & Prichard R K (1999) Haemonchous contortus - effects of glutamate, ivermectin, and moxidectin on insulin activity in unselected and ivermectin-selected adults. Exp Parasitol 92 (3), 193-198.
• Paradis M (1999) New approaches to the treatment of canine demodicosis. Vet Clin North Am Small Anim Pract 29 (6), 1425-1436.
• Paradis M (1998) Ivermectin in small animal dermatology. Part II - extralabel applications. Comp Cont Ed Prac Vet 20 , 459-469.
• Nuttall T J, French A T, Cheetham H C & Proctor F J (1998) Treatment of trombicula autumnalis infection in dogs and cats with a 0.25% fipronil pump spray. JSAP 39 , 237-239.
• Cooper P R & Penaliggon J (1996) Use of fipronil to eliminate recurent infestation by Trichodectes canis in a pack of bloodhounds. Vet Rec 139 , 95.
• Hugnet C et al(1996) Toxicity and kinetics of amitraz in dogs. Am J Vet Res 57 (10), 1056-1510.
• Barriga O O (1991) Rational control of canine toxocariasia by the vaterinary practioner. JAVMA 198 (2), 216-221.
• Harvey J B, Roberts J M & Schantz P M (1991) Survey of veterinarians' recommendations for treatment and control of interstinal parasites in dogs - public health implications. JAVMA 199 (6), 702-707.
• Paul A J, Tranquilli W J, Todd K S, Wallace D H & Soll M (1991) Evaluating the safety of administering high doses of a chewable ivermectin tablet to Collies. Vet Med 86 (6), 623-625.

Other sources of information

• T K Shotwell (1999) The Complete Handbook of Apporoved New Animal Drug Applications in the United States. Carr Inc. Texas, USA.
• Kunkle G (1997) An updated review of ectoparasiticide treatments in dogs and cats. Proceedings of the 7th European Association for Veterinary Pharmacology and Toxicology International Congress, Madrid, Spain. 6-10 July.
• Lynn R C (1995) Antiparasitic Drugs. In: Georgis' Parasitology for Veterinarians.6th edn. W B Saunders, Philadelphia. pp 247-292.
• Courtney C H & Sundlof S F (1991) Veterinary Antiparasiteic Drugs. Am Assoc Vet Parasitol, University of Florida Publication SP96, Gainesville, Florida.