ISSN 2398-2942      

Therapeutics: parasiticide




Drugs for nematodesAvermectins and milbemycins

  • IvermectinIvermectin - used to control migrating heartworm larvae.
    Approved in US only as a preventative for heartworm.Toxicity Ivermectin 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 Streptomycesspp 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 Milbemycin oxime.


  • 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 Albendazole : lungworm - Oslerus (formerly known as FilaroidesOslerus (Filaroides) osleri.
    Teratogenic in early pregnancy.
  • Fenbendazole Fenbendazole : for pregnant and lactating bitches to prevent roundworm in puppies, also for hookworms, whipworms, lungworm and tapeworm ( Taenia Taenia pisiformis - not licensed for Echinococcus or Dipylidium). Needs daily treatment from day 40 of pregnancy through to 2 days post-partum to achieve this.
  • Mebendazole Mebendazole : gastrointestinal roundworms, Echinococcus Echinococcus granulosus and Taenia Taenia pisiformis. Need to treat longer if treating tapeworms.
  • Praziquantel Praziquantel : preferred treatment for Echinococcus Echinococcus granulosus.
  • Febantel Febantel.


  • 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 hydrochlorideLevamisole : lungworms ( Angiostrongylus Angiostrongylus vasorum ), immune stimulation, heartworm treatment (seek specialist advice).

Organophosphorous compounds

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


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


  • Nitroscanate Nitroscanate : roundworms and tapeworms (at recommended dose it gives only limited control of echinococcus).
  • Piperazine Piperazine : modifies neurotransmission → relaxation and expulsion; for some roundworms, ie Toxocara, Toxascaris Toxocara canis and Uncinaria; little activity against larval Toxocarain 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 lupiat very high doses.


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

Drugs for tapeworms

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

  • Dichlorophen Dichlorophen : effective against Dipylidium and Taenia.
  • Praziquantel 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 Fenbendazole : effective against Taenia spp.

Compound endoparasiticides

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


  •  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 al,1991), fenbendazole 50 mg/kg for 10-14 d (Dubey et al,1979), albendazole 25 mg/kg BID for 14 d.
    •  N. salmincola - praziquantel 7-38 mg SQ or IM (Foreyt & Gorham, 1988).


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Mealey K L (2008) Canine ABCB1 and macrocyclic lactones: heartworm prevention and pharmacogenetics. Vet Parasitol 158 (3), 215-222 PubMed.
  • Estrada-Peña 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 PubMed.
  • Marsella R (1999) Advances in flea control. Vet Clin North Am Small Anim Pract 29 (6), 1407-1424 PubMed.
  • Paiement J P, Leger C, Ribeiro P et al (1999) Haemonchus contortus - effects of glutamate, ivermectin, and moxidectin on inulin uptake activity​ in unselected and ivermectin-selected adults. Exp Parasitol 92 (3), 193-198 PubMed.
  • Paradis M (1999) New approaches to the treatment of canine demodicosis. Vet Clin North Am Small Anim Pract 29 (6), 1425-1436 PubMed.
  • Nuttall T J, French A T, Cheetham H C et al (1998) Treatment of trombicula autumnalis infection in dogs and cats with a 0.25% fipronil pump spray. JSAP 39 (5), 237-239 PubMed.
  • Paradis M (1998) Ivermectin in small animal dermatology. Part II. Extralabel applications. Comp Cont Ed Prac Vet 20 (4), 459-484 VetMedResource.
  • Cooper P R & Penaliggon J (1996) Use of fipronil to eliminate recurent infestation by Trichodectes canis in a pack of bloodhounds. Vet Rec 139 (4), 95 PubMed.
  • Hugnet C, Buronrosse F, Pineau X et al (1996) Toxicity and kinetics of amitraz in dogs. Am J Vet Res 57 (10), 1506-1510 PubMed.
  • Barriga O O (1991) Rational control of canine toxocariasis by the veterinary practioner. JAVMA 198 (2), 216-221 PubMed.
  • 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 PubMed.
  • Paul A J, Tranquilli W J, Todd K S et al (1991) Evaluating the safety of administering high doses of a chewable ivermectin tablet to Collies. Vet Med 86 (6), 623-625 VetMedResource.

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.

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