Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.


Chemistry - A benzimidazole anthelmintic, fenbendazole occurs as a white, crystalline powder. It isonly slightly soluble in water.

Storage, Stability, Compatibility

Fenbendazole products should be stored at room temperature.

Uses, Indications

Fenbendazole is indicated (labeled) for the removal of the following parasitesin dogs: ascarids (Toxocara canis, T. leonina), Hookworms (Ancylostoma caninum, Uncinariastenocephala), whipworms (Trichuris vulpis), and tapeworms (Taenia pisiformis). It is not effectiveagainst Dipylidium caninum. Fenbendazole has also been used clinically to treat Capillariaaerophilia:, Filaroides hirthi and Paragonimus kellicoti infections in dogs.
Fenbendazole is indicated (labeled) for the removal of the following parasites in cattle: Adultforms of: Haemonchus contortus, Ostertagia ostertagi, Trichostrongylus axei, Bunostomumphlebotomum, Nematodirus helvetianus, Cooperia spp., Trichostrongylus colubriformis,
Oesophagostomum radiatum and Dictyocaulus vivaparus. It is also effective against most immature stages of the above listed parasites. Although not approved, it also has good activity against
Moniezia spp., and arrested 4th stage forms of Ostertagia ostertagi.
Fenbendazole is indicated (labeled) for the removal of the following parasites in horses: largestrongyles (S. edentatus, S. equinus, S. vulgaris), small strongyles (Cyathostomum spp.,
Cylicocylus spp., Cylicostephanus spp., Triodontaphorus spp.) and pinworms (Oxyuris equi).
Fenbendazole is indicated (labeled) for the removal of the following parasites in swine: large roundworms (Ascaris suum), lungworms (Metastrongylus apri), nodular worms (Oesphagostomum dentatum, O. quadrispinulatum), small stomach worms (Hyostrongylus rubidus), whipworms (Trichuris suis) and kidney worms (Stephanuris dentatus; both mature and immature).
Although not approved, fenbendazole has been used in cats, sheep, goats, pet birds and llamas. See Dosage section for more information.
Fenbendazole is considered to be safe to use in pregnant bitches and is generally considered to besafe to use in pregnancy for all species.

Pharmacokinetics - FENBENDAZOLE

Fenbendazole is only marginally absorbed after oral administration. After oraldosing in calves and horses, peak blood levels of 0.11 micrograms/ml and 0.07 micrograms/mlrespectively, were measured. Absorbed fenbendazole is metabolized (and vice-versa) to the activecompound, oxfendazole (sulfoxide) and the sulfone. In sheep, cattle, and pigs, 44-50% of a dose offenbendazole is excreted unchanged in the feces, and <1% in the urine.
Contraindications/Precautions - Fenbendazole is not approved for use in lactating dairy cat le orfor horses intended for food purposes.

Adverse Effects, Warnings

At usual doses, fenbendazole generally does not cause any adverseeffects. Hypersensitivity reactions secondary to antigen release by dying parasites may occur;particularly at high dosages. Vomiting may infrequently occur in dogs or cats receiving fenbendazole.
Single doses (even at exaggerated doses) are not effective in dogs and cats; must treat for 3 days.
Overdosage/Toxicity - Fenbendazole is apparently well tolerated at doses up to 100X recommended. The LD50 in laboratory animals exceeds 10 grams/kg when administered PO. It is unlikely an acute overdosage would lead to clinical symptoms.

Drug Interactions

Oxfendazole or fenbendazole should not be given concurrently with thebromsalan flukicides (Dibromsalan, Tribromsalan). Abortions in cattle and death in sheephave been reported after using these compounds together.