Fenbendazole is a broad-spectrum anthelmintic belonging to the benzimidazoles, effective against roundworms and, depending on the dose, also against some tapeworms (e.g. Moniezia spp) as well. It is ineffective against flukes (e.g. Fasciola hepatica adults) at the usual therapeutic dose. It is completely ineffective against external parasites.
Today’s parasite researchers recommend using two classes of dewormers for effectiveness and to help curb resistance issues. Widespread use of an endectocide (like ivermectin) to control both internal and external parasites should be accompanied by a benzimidazole (like Safe-Guard) to get the tough internal parasites and fight against resistance.
Oral administration is the rule. It is used massively in all kinds of livestock (mainly in drenches and feed additives), and abundantly in pets (often in tablets, pills, etc. or oral suspensions) and horses (mostly in oral pastes & gels). There are hundreds of generic brands worldwide, also in mixtures with other anthelmintics. Unfortunately, resistance of gastrointestinal roundworms to all benzimidazoles in sheep, goats, cattle and horses is a major problem in numerous countries. Not so yet in pets, swine or poultry.
In ruminants, a 50% reduction of the diet 36 prior and 8 hours after treatment slows down the passage through the stomach, which increases the bioavailability of benzimidazoles and their metabolites and consequently its efficacy against gastrointestinal parasites.
Uses/benefits of Fenbendazole For Cows
Fenbendazole is absorbed slowly in the stomach. Therefore the longer it remains there, the better the efficacy. In carnivores (e.g. dogs and cats) and other animals with a simple stomach the passage through the stomach is rather fast and therefore a higher dosage is required. This is why it is more often used on livestock than on dogs and cats.
In ruminants, unless delivered using a slow-release device, fenbendazole has only a limited residual effect. This means that a single administration will kill the parasites present in the host at the time of treatment and protect against re-infestations for a few more days, but not for weeks or months. In non-ruminants the residual effect is substantially shorter, i.e. only a few hours.
At the therapeutic dose fenbendazole is not effective against flukes and whatsoever external parasites. Unfortunately, resistance of several gastrointestinal roundworms to all benzimidazoles,, including fenbendazole is already very high and very frequent worldwide in sheep and goats, slightly lower in cattle. For this reason, the risk that benzimidazoles fail to protect ruminants against gastrointestinal roundworms is considerable worldwide. Resistance of worms to benzimidazoles in dogs, cats, pig and poultry are so far not a serious problem.
Dose (against fenbendazole-susceptible parasites)
1 mg/kg/day x5-10 days, mixed with feed
5-7.5 mg/kg, rep after 4 weeks if needed
Fasciola hepatica, adults
15 mg/kg/day x6 days
Ostertagia ostertagi inhibited larvae
10 mg/kg 2x/day x 3 days
NOT FOR USE IN HUMANS. KEEP OUT OF REACH OF CHILDREN. The Safety Data Sheet (SDS) contains more detailed occupational safety information. For customer service, adverse effects reporting, and/or a copy of the SDS, call 1-800-211-3573. For additional information about adverse drug experience reporting for animal drugs, contact FDA at 1-888-FDAVETS,
Parasite resistance may develop to any dewormer, and has been reported for most classes of dewormers. Treatment with a dewormer used in conjunction with parasite management practices appropriate to the geographic area and the animal(s) to be treated may slow the development of parasite resistance. Fecal examinations or other diagnostic tests and parasite management history should be used to determine if the product is appropriate for the herd, prior to the use of any dewormer. Following the use of any dewormer, effectiveness of treatment should be monitored (for example, with the use of a fecal egg count reduction test or another appropriate method). A decrease in a drug’s effectiveness over time as calculated by fecal egg count reduction tests may indicate the development of resistance to the dewormer administered. Your parasite management plan should be adjusted accordingly based on regular monitoring.