Fenbendazole (CAS 43210-67-9)

Fenbendazole (Hoechst brand names Panacur and Safe-Guard, Intervet Panacur and Panacur Rabbit)

is a broad spectrum benzimidazole anthelmintic used against gastrointestinal parasites including:

giardia, roundworms, hookworms, whipworms, the Taenia genus of tapeworms (but not effective against

Dipylidium caninum, a common dog tapeworm), pinworms, aelurostrongylus, paragonimiasis, strongyles

and strongyloides and can be administered to sheep, cattle, horses, fish, dogs, cats, rabbits and seals. Drug

interactions may occur if salicylanilides like dibromsalan and niclosamide are co-adminstered. Abortions

in cattle and death in sheep have been reported.

Toxicity

Despite being widely used as a dewormer in many species, toxicity has been reported. Birds (storks, pink

pelicans, vultures, pigeons and doves) and reptiles (vipers, turtles and tortoises) have shown toxicity

associated with bone marrow suppression, intestinal crypt cell necrosis and distal villi sloughing

.[citation needed] Abortions in domestic ruminants have been associated with concurrent use

of anti-trematode therapeutic agents.

Fenbendazole is poorly absorbed from the gastrointestinal tract in most species. The LD50 in

laboratory animals exceeds 10 g/kg when administered orally.

Synthesis

Fenbendazole synthesis

Metabolism

It gets metabolized in the liver to oxfendazole, which is anthelmintic too; oxfendazole partially

gets reduced back to fenbendazole in the liver and rumen. Also, fenbendazole itself is an

active metabolite of another anthelmintic drug, febantel.