Fenbendazole

Fenbendazole is a benzimidazole anthelmintic used across companion-animal and livestock species. It acts against many gastrointestinal nematodes and selected lungworms, with additional applications for Giardia in dogs and some other hosts. Its spectrum varies with species, parasite stage and regimen, and its active metabolite oxfendazole contributes to antiparasitic activity.

Group

Benzimidazole anthelmintic

Mechanism of Action

Fenbendazole binds parasite beta-tubulin and inhibits microtubule polymerization. Loss of microtubule-dependent transport disrupts intestinal-cell function and glucose uptake, progressively depleting energy stores and causing parasite death. Differential affinity for parasite tubulin contributes to selective activity. Related disruption of microtubule function is also implicated in its antigiardial effects.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Intestinal nematodes	50 mg/kg	PO	Every 24 h	Up to 3 days
Severe intestinal nematodes	50 mg/kg	PO	Every 24 h	Up to 5 days
Lungworms	50 mg/kg	PO	Every 24 h	Up to 14 days; 10–14-day course.
Giardiasis	50 mg/kg	PO	Every 24 h	Up to 5 days; 3–5-day course.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Intestinal nematodes	50 mg/kg	PO	Every 24 h	Up to 3 days
Severe intestinal nematodes	50 mg/kg	PO	Every 24 h	Up to 5 days
Pancreatic fluke infection	30 mg/kg	PO	Every 24 h	Up to 6 days; Eurytrema procyonis.
Capillaria feliscati	25 mg/kg	PO	Every 12 h	Up to 10 days; Described courses range from 3–10 days.

Horse

Use / stage	Dose	Route	Schedule	Instructions
Intestinal nematodes	5 mg/kg	PO	Once	Paste regimen; retreatment in 6–8 weeks may be needed.
Intestinal nematodes	5.1 mg/kg	PO	Once	Alternative granule regimen.
Ascarids	10 mg/kg	PO	Once

Sheep

Use / stage	Dose	Route	Schedule	Instructions
Intestinal nematodes	5 mg/kg	PO	Once

Goat

Use / stage	Dose	Route	Schedule	Instructions
Intestinal nematodes	5 mg/kg	PO	Once

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Intestinal nematodes	5 mg/kg	PO	Once
In-feed parasite treatment	5 mg/kg	PO	Every 24 h	Up to 6 days; Course 3–6 days.

Mouse

Use / stage	Dose	Route	Schedule	Instructions
Pinworm infection	50 mg/kg	PO	Once
Susceptible intestinal parasites	20–50 mg/kg	PO	Every 24 h	Up to 5 days; Higher end used for Giardia.

Rat

Use / stage	Dose	Route	Schedule	Instructions
Pinworm infection	50 mg/kg	PO	Once
Susceptible intestinal parasites	20–50 mg/kg	PO	Every 24 h	Up to 5 days; Higher end used for Giardia.

Hamster

Use / stage	Dose	Route	Schedule	Instructions
Pinworm infection	50 mg/kg	PO	Once
Susceptible intestinal parasites	20–50 mg/kg	PO	Every 24 h	Up to 5 days; Higher end used for Giardia.

Gerbil

Use / stage	Dose	Route	Schedule	Instructions
Pinworm infection	50 mg/kg	PO	Once
Susceptible intestinal parasites	20–50 mg/kg	PO	Every 24 h	Up to 5 days; Higher end used for Giardia.

Rabbit

Use / stage	Dose	Route	Schedule	Instructions
Pinworm infection	50 mg/kg	PO	Once

Guinea Pig

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	20–50 mg/kg	PO	Every 24 h	Up to 5 days; Higher end used for Giardia.

Chinchilla

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	20–50 mg/kg	PO	Every 24 h	Up to 5 days; Higher end used for Giardia.
Giardiasis	25 mg/kg	PO	Every 24 h	Up to 3 days

Large Cat

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	10 mg/kg	PO	Every 24 h	Up to 3 days; Large exotic cats or bears as specified for this regimen; not domestic-cat dosing.

Bear

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	10 mg/kg	PO	Every 24 h	Up to 3 days; Large exotic cats or bears as specified for this regimen; not domestic-cat dosing.

Llama

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	10–20 mg/kg	PO	Every 24 h	Up to 5 days; Described course 3–5 days.
Meningeal worm adjunct	Reference only	PO		Fenbendazole 50 mg/kg orally daily for five days with ivermectin 0.3 mg/kg SC daily for five days, plus anti-inflammatory, ulcer-prevention and supportive therapy.

Alpaca

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	10–20 mg/kg	PO	Every 24 h	Up to 5 days; Described course 3–5 days.
Meningeal worm adjunct	Reference only	PO		Fenbendazole 50 mg/kg orally daily for five days with ivermectin 0.3 mg/kg SC daily for five days, plus anti-inflammatory, ulcer-prevention and supportive therapy.

Ratite

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	15 mg/kg	PO	Every 24 h	Up to 3 days; Includes reported activity against ostrich tapeworm.

Reptile

Use / stage	Dose	Route	Schedule	Instructions
Susceptible intestinal parasites	50–100 mg/kg	PO		Repeat once in 2–3 weeks; reported activity against Strongyloides.

Bird

Use / stage	Dose	Route	Schedule	Instructions
Flukes or microfilariae	10–50 mg/kg	PO	Every 24 h	Up to 3 days; Do not use in: Molting, Nesting or breeding
Capillaria infection	10–50 mg/kg	PO	Every 24 h	Up to 5 days; Do not use in: Molting, Nesting or breeding
Ascarid infection	10–50 mg/kg	PO		Do not use in: Molting, Nesting or breeding; Repeat in ten days; not effective against finch gizzard worms.

Pig

Use / stage	Dose	Route	Schedule	Instructions
Potbellied-pig whipworm protocol	Reference only	PO		The source gives 9 mg/kg but the duration is printed only as “for days”; a complete course cannot be determined.

Indications

Treatment of susceptible intestinal roundworms, hookworms and whipworms in dogs and selected other companion animals.
Treatment of selected lungworm infections in dogs and cats using a parasite-specific regimen.
Treatment of canine giardiasis and selected extra-label Giardia infections in other veterinary patients, with variable clearance rates.
Treatment of susceptible strongyles, ascarids and pinworms in horses, including selected larval stages with an appropriate regimen.
Treatment and control of susceptible gastrointestinal nematodes and lungworms in cattle, sheep, goats or pigs with a corresponding veterinary product.

Contraindications

No specific source contraindication identified.

Adverse effects

Vomiting and diarrhea
Rare pancytopenia

Preparations

Preparation	Form	Strength	Route
Fenbendazole granules 222 mg/g	Granules	222 mg / g	PO
Fenbendazole oral suspension 100 mg/mL	Oral Liquid	100 mg / mL	PO
Fenbendazole paste 10%	Paste	100 mg / g	PO
Fentas bolus 1500 mg Intas Pharmaceuticals Ltd.	Tablet	1500 mg / tablet	PO
Fentas bolus 3000 mg Intas Pharmaceuticals Ltd.	Tablet	3000 mg / tablet	PO
Fentas Plus tablet Intas Pharmaceuticals Ltd. Combination; follow its regimen rather than substituting into all single-drug courses.	Tablet	fenbendazole 150 mg / tablet + praziquantel 50 mg / tablet	PO

Monitoring and Administration

Granules can be mixed with food; confirm efficacy by appropriate fecal or parasitologic testing. Giardia response is variable.

Duration differs by parasite and severity. Source reports pregnancy tolerance.