# Fenbendazole

Fenbendazole is a broad spectrum benzimidazole anthelmintic used against gastrointestinal parasites including: giardia, roundworms, hookworms, whipworms, the tapeworm genus Taenia (but not effective against Dipylidium caninum, a common dog tapeworm), pinworms, aelurostrongylus, paragonimiasis, strongyles, and strongyloides that can be administered to sheep, cattle, horses, fish, dogs, cats, rabbits, most reptiles, freshwater shrimp tanks as planaria and hydra treatments, as well as seals.

## Mechanism of action

Fenbendazole works by binding to tubulin, a protein that is part of the microtubules in the cells of parasites. This binding disrupts the microtubules' formation and function, leading to the parasites' inability to absorb nutrients, resulting in their eventual death. This mode of action makes fenbendazole effective against both adult and larval stages of many parasitic worms.

## Uses in veterinary medicine
### Dogs and cats

Fenbendazole is commonly used to treat intestinal parasites, including roundworms, hookworms, whipworms, and certain tapeworms. It is often administered as part of a broader deworming protocol.

### Horses

In equine medicine, fenbendazole is used to control strongyles, pinworms, and ascarids. It is available in paste form for easy administration.

### Cattle and goats

Fenbendazole is effective against lungworms, stomach worms, and intestinal worms in ruminants. It is administered through feed, drenching, or bolus form.

## History

Fenbendazole was first developed by German scientists in the early 1970s. It belongs to the benzimidazole class of compounds, which are known for their ability to disrupt the microtubule structure of parasites. Microtubules are essential for cellular functions such as maintaining shape and facilitating cell division. Fenbendazole works by binding to beta-tubulin proteins, preventing proper microtubule formation, which ultimately leads to the death of the parasite.
Fenbendazole was first approved for use in dogs on November 2, 1983. It became widely adopted in veterinary medicine due to its efficacy and safety profile. It was used to treat parasitic infestations in various animals, including dogs, cats, livestock, and poultry.

## Drug interactions

Drug interactions may occur if salicylanilides such as dibromsalan and niclosamide are co-administered. Abortions in cattle and death in sheep have been reported after using these medications together. Abortions in domestic ruminants have been associated with concurrent use of anti-trematode therapeutic agents.

## Dosage and administration

The appropriate dosage of the medication fenbendazole depends on the specific animal species being treated as well as the particular formulation or preparation of the fenbendazole product being used. To ensure the correct dosage considering the animal species being treated with its weight, using a dosage calculator like the Fenbendazole Paraclear Defense Dosage Calculator would be recommended.

## Toxicity

Fenbendazole is poorly absorbed from the gastrointestinal tract in most species. The LD$_{50}$ in laboratory animals exceeds 10 g/kg when administered orally.

## Metabolism

Fenbendazole is 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.

## Safety and precautions

Fenbendazole is generally safe when used as directed. However, it is important to follow veterinary guidelines and dosage instructions to avoid potential side effects. Some animals may experience mild gastrointestinal upset. It is not recommended for use in pregnant animals without veterinary advice.

## Repurposing

Fenbendazole has been proposed for repurposing as an anticancer drug due to its ability to disrupt energy metabolism in cancer cells and induce cell death through multiple mechanisms. However, its poor bioavailability when administered orally remains a challenge for its repurposing as a cancer treatment.