Chemistry - A benzimidazole anthelmintic, fenbendazole occurs as a white, crystalline powder. It is only slightly soluble in water.
Storage/Stability/Compatibility - Fenbendazole products should be stored at room temperature.
Uses/Indications - Fenbendazole is indicated (labeled) for the removal of the following parasites in dogs: ascarids (Toxocara canis, T. leonina), Hookworms (Ancylostoma caninum, Uncinaria stenocephala), whipworms (Trichuris vulpis), and tapeworms (Taenia pisiformis). It is not effective against Dipylidium caninum. Fenbendazole has also been used clinically to treat Capillaria aerophilia:, Filaroides hirthi and Paragonimus kellicoti infections in dogs.
Fenbendazole is indicated (labeled) for the removal of the following parasites in cattle: Adult forms of: Haemonchus contortus, Ostertagia ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Nematodirus helvetianus, Cooperia spp., Trichostrongylus colubriformis, Oesophagostomum radiatum and Dictyocaulus vivaparus. It is also effective against most immature stages of the above listed parasites. Although not approved, it also has good activity against Moniezia spp., and arrested 4th stage forms of Ostertagia ostertagi.
Fenbendazole is indicated (labeled) for the removal of the following parasites in horses: large strongyles (S. edentatus, S. equinus, S. vulgaris), small strongyles (Cyathostomum spp., Cylicocylus spp., Cylicostephanus spp.,Triodontaphorus spp.) and pinworms (Oxyuris equi).
Fenbendazole is indicated (labeled) for the removal of the following parasites in swine: large roundworms (Ascaris suum), lungworms (Metastrongylus apri), nodular worms (Oesphagostomum dentatum, O. quadrispinulatum), small stomach worms (Hyostrongylus rubidus), whipworms (Trichuris suis) and kidney worms (Stephanuris dentatus; both mature and immature).
Although not approved, fenbendazole has been used in cats, sheep, goats, pet birds and llamas. See Dosage section for more information.
Fenbendazole is considered to be safe to use in pregnant bitches and is generally considered to be safe to use in pregnancy for all species.
Pharmacokinetics - Fenbendazole is only marginally absorbed after oral administration. After oral dosing in calves and horses, peak blood levels of 0.11 micrograms/ml and 0.07 micrograms/ml respectively, were measured. Absorbed fenbendazole is metabolized (and vice-versa) to the active compound, oxfendazole (sulfoxide) and the sulfone. In sheep, cattle, and pigs, 44-50% of a dose of fenbendazole is excreted unchanged in the feces, and <1% in the urine.
Contraindications/Precautions - Fenbendazole is not approved for use in lactating dairy cattle or for horses intended for food purposes.
Adverse Effects/Warnings - At usual doses, fenbendazole generally does not cause any adverse effects. Hypersensitivity reactions secondary to antigen release by dying parasites may occur; particularly at high dosages. Vomiting may infrequently occur in dogs or cats receiving fenbendazole.
Single doses (even at exaggerated doses) are not effective in dogs and cats; must treat for 3 days.
Overdosage/Toxicity - Fenbendazole is apparently well tolerated at doses up to 100X recommended. The LD50 in laboratory animals exceeds 10 grams/kg when administered PO. It is unlikely an acute overdosage would lead to clinical symptoms.
Drug Interactions - Oxfendazole or fenbendazole should not be given concurrently with the bromsalan flukicides (Dibromsalan, Tribromsalan). Abortions in cattle and death in sheep have been reported after using these compounds together.
For susceptible parasites:
a) 5 mg/kg PO; 10 mg/kg once daily for 5 days to treat S. vulgaris in foals. (Robinson 1987)
b) 5 mg/kg PO; 10 mg/kg for ascarids. (Roberson 1988b)
c) For treatment of migrating large strongyles: 50 mg/kg PO for 3 consecutive days, or 10 mg/kg for 5 consecutive days. (Herd 1987)
a) 5 mg/kg po (Raman, et.al., 2000).
b) 2.5 mg/kg orally as a single dose (Chandrasekharan,2002);(Chandrasekharan et.al.,1995).
c) 2.0 –2.5 mg/kg orally as a single dose mixed with jaggery or rice (Chandrasekharan, 1992).
d) 5 mg/kg po in feed as a single dose (Strao et.al., 1992).
e) Chronic murshidiasis in an Asian elephant was resolved with 50 g fenbendazole repeated at 30 days (Tripathy et.al. 1991).
f) 5 mg/kg po as a single dose (Roy and Mazumdar, 1988).
g) 12 g of Panacur dissolved in 2000 ml water in 2 divided doses at a 3 -day interval (Lahkar and Das,1988).
b) Chandrasekharan,K. 2002. Specific diseases of Asian elephants. Journal of Indian Veterinary Association Kerala 7:(3):31-34
b) Chandrasekharan,K., Radhakrishnan,K., Cheeran,J.V., Nair,K.N.M., and Prabhakaran,T., 1995. Review of the Incidence, Etiology and Control of Common Diseases of Asian Elephants with Special Reference to Kerala. In: Daniel,J.C. (Editor), A Week with Elephants; Proceedings of the International Seminar on Asian Elephants. Bombay Natural History Society; Oxford University Press, Bombay, India pp. 439-449
c) Chandrasekharan,K., 1992. Prevalence of infectious diseases in elephants in Kerala and their treatment. In: Silas,E.G., Nair,M.K., and Nirmalan,G. (Editors), The Asian Elephant: Ecology, Biology, Diseases, Conservation and Management (Proceedings of the National Symposium on the Asian Elephant held at the Kerala Agricultural University, Trichur, India, January 1989). Kerala Agricultural University, Trichur, India pp. 148-155
d) Rao, D.S.T., Yathiraj, S., Choudhuri, P.C., and
Reddy, P.K. 1992. Treatment of helminthiosis in elephants. Indian
Journal of Animal Science 62(12):1155-1156.
and Mazumdar,B.K. 1988. Anthelmintic activity of fenbendazole (Panacur)
against Murshidia murshida in zoo elephants. Indian Veterinary Journal
g) Lahkar,B.C. and Das,M.R. 1988. A note on the successful treatment of trichostrongyle infection of elephants (Elephas maximus) with Panacur (fenbendazole). Indian Veterinary Journal 65:(6):538 Summary: Six Indian elephants, E. maximus infected with gastrointestinal nematodes (700-1400 epg faeces) were given 12 g Panacur (fenbendazole) in the form of a bolus with flour, in 2 doses 3 days part. Faecal samples from all animals were negative 3 days after the second dose. No side effects were recorded.
Dosage Forms/Preparations/FDA Approval Status -
Fenbendazole Granules 222 mg/gram (22.2%) in 0.18 oz & 1 g, 2 g, 4 g packets and 1 lb jars; Panacur® Granules 22.2% (Hoechst). (Rx) Approved for use in dogs.
Fenbendazole Granules 222 mg/gram (22.2%); Panacur® Granules 22.2% (Hoechst). (OTC) Approved for use in horses not intended for food.
Fenbendazole Suspension 100 mg/ml (10%); available in both equine and bovine labeled products; Panacur® Suspension (Hoechst). (Rx) Approved for use in horses (not intended for food) and cattle Slaughter withdrawal=8 days (cattle). Safe-Guard® Suspension (Hoechst) (OTC) Approved for use in beef and dairy cattle. Slaughter withdrawal = 8 days
Fenbendazole Paste 100 mg/gram (10%); available in both equine and bovine labeled products and sizes. Panacur® Paste (Hoechst). (OTC) Approved for use in horses (not intended for food) and cattle. Slaughter withdrawal=8 days (cattle). Safe Guard Paste® (Hoechst) (OTC) Approved for use in horses not intended for food and cattle. Slaughter withdrawal = 8 days; no milk withdrawal time.
Fenbendazole Medicated Block 750 mg/lb.; 25 lb. block; Safe-Guard Sweetlix® (Hoechst); (OTC) Approved for use in beef cattle. Slaughter withdrawal= 16 days.
Fenbendazole Type B Medicated Feed
Safe-Guard EZ Scoop Swine Dewormer® (Hoechst) (OTC). 1.8% Fenbendazole No slaughter withdrawal time required
Safe-Guard 0.96% Scoop Dewormer® (Hoechst) (OTC) Approved for use in cattle. No milk withdrawal time; slaughter withdrawal time=13 days
Fenbendazole Type C Medicated Feed
Safe-Guard Free-choice Cattle Dewormer® (Hoechst) (OTC). 0.50% Fenbendazole (2.27 g/lb) Approved for use in beef and dairy cattle. No milk withdrawal time.
Safe-Guard 35% Salt Free-choice Cattle Dewormer® (Hoechst) (OTC) 1.9 g/lb Fenbendazole. Approved for use in dairy and beef cattle. Slaughter withdrawal time=13 days; no milk withdrawal time.
Safe-Guard 0.5% Cattle Top Dress® (Hoechst) (OTC) Slaughter withdrawal time=13 days; no milk withdrawal period
Safe-Guard 1.96% Scoop Dewormer Mini Pellets® (Hoechst) (OTC) Approved for use in beef and dairy cattle. No milk withdrawal time; slaughter withdrawal time=13 days
Fenbendazole Premix 20% Type A (200 mg/gram)
Safe-Guard Premix® (Hoechst). (OTC) Approved for use in swine. dairy and beef cattle, zoo & wildlife animals. Slaughter withdrawal for cattle = 13 days; no milk withdrawal time. Slaughter withdrawal for swine=none. Wildlife animal slaughter (hunting) withdrawal = 14 days.
Human-Approved Products: None
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