Fenbendazole belongs to a class of drugs known as anthelmintics. This drug is often used to remove various gastrointestinal parasites from animals. Fenbendazole is effective against roundworms, hookworms, whipworms, certain tapeworms and parasites called strongyles and strongyloides. Fenbendazole is also effective against certain parasites of the bronchial tree and lungs (Aelurostrongylus and Paragonimiasis).

It binds to 3-tubulin astructural protein that blocks polymerization of tubulin into microtubules, which damages the integrity and the transport function of cells in parasites. The reason behind the wide safety margin is due to its affinity to the parasitic tubules rather than mamilian.

In dogs, it is useful against roundworms, hookworms, and the more difficult to treat whipworms. It is effective against the Taenia species of tapeworm but not against the Common tapeworm Dipylidium caninum. It is also effective against Giardia, a protozoan and several species of lungworm and even some flukes. Fenbendazole is rarely required for feline use though can certainly be used safely in cats, but Fenbendazole is not approved for use in cats by the FDA.

Formal Chemical Name (IUPAC)
methyl 5-(phenylthio)-1H-benzo[d]imidazol-2-ylcarbamate

References

http://en.wikipedia.org/wiki/Fenbendazole

http://www.petplace.com/drug-library/fenbendazole-panacur/page1.aspx