Chemistry - A benzimidazole anthelmintic, oxfendazole occurs as white or almost white powder possessing a characteristic odor. It is practically insoluble in water. Oxfendazole is the sulfoxide metabolite of fenbendazole.
Storage/Stability/Compatibility - Unless otherwise directed by the manufacturer, oxfendazole products should be stored at room temperature and protected from light. The manufacturer recommends discarding any unused suspension 24 hours after it has been reconstituted.
Uses/Indications - Oxfendazole is indicated (labeled) for the removal of the following parasites in horses: large roundworms (Parascaris equorum), large strongyles (S. edentatus, S. equinus, S. vulgaris), small strongyles and pinworms (Oxyuris equi).
Oxfendazole has also been used in cattle, sheep, goats, and swine; see Dosage section for more information.
Pharmacokinetics - Limited information is available regarding this compound’s pharmacokinetics. Unlike most of the other benzimidazole compounds, oxfendazole is absorbed more readily from the GI tract. The elimination half-life has been reported to be about 7.5 hours in sheep and 5.25 hours in goats. Absorbed oxfendazole is metabolized (and vice-versa) to the active compound, fenbendazole (sulfoxide) and the sulfone.
Contraindications/Precautions - There are no contraindications to using this drug in horses, but it is recommended to use oxfendazole cautiously in debilitated or sick horses. Oxfendazole may be safely used in pregnant mares and foals.
Adverse Effects/Warnings - When used as labeled, it is unlikely any adverse effects will be noted. Hypersensitivity reactions secondary to antigen release by dying parasites are theoretically possible, particularly at high dosages.
Overdosage/Toxicity - Doses of 10 times those recommended elicited no adverse reactions in horses tested. It is unlikely that this compound would cause serious toxicity when given alone.
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: 10 mg/kg PO. (Package insert; Benzelmin®—Syntex), (Roberson 1988b)
For susceptible parasites:
a) 4.5 mg/kg PO. (Roberson 1988b)
b) 5 mg/kg PO. (Brander, Pugh, and Bywater 1982)
Monitoring Parameters - Efficacy
Client Information - Not to be used in horses intended for food purposes.
Dosage Forms/Preparations/FDA Approval Status -
Veterinary-Approved Products: None
Oxfendazole Powder for Suspension 75.6 mg/gram in 30 gram packets and 300 gram bulk powder.
Benzelmin® (Fort Dodge); (Rx) Approved for use in horses.
Oxfendazole Suspension 90.6 mg/ml in 1 liter bottles.
Benzelmin® (Fort Dodge); (Rx) Approved for use in horses. Shake well before using.
Oxfendazole Oral Paste 375 mg/gram in 12 g and 72 g syringes. Benzelmin® Paste (Fort Dodge); (OTC) Approved for use in horses.
Oxfendazole may be known in the U.K. by the proprietary names: Synanthic® (Syntex) or Systamex® (Coopers).
Human-Approved Products: None
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