Oxfendazole
Oxfendazole (sulfoxide metabolite of fenbendazole)
Also known as: Synanthic · Benzelmin · RS 8858
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For Oslerus osleri | 10 mg/kg PO once daily for 28 days. | PO | q24h | 28 days | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For susceptible parasites | 10 mg/kg PO | PO | Single dose | — | 🌎 NA |
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For susceptible parasites | 4.5 mg/kg either PO or via intraruminal injection (22.5% only). May repeat in 4-6 weeks. Dose of the 9.06% suspension is 2.5 mL per 100 lb (50 kg) of body weight PO. Dose of the 22.5% suspension is 1 mL per 100 lb (50 kg) of body weight either PO or intraruminal injection. | PO/intraruminal | Single dose, may repeat in 4-6 weeks | — | 🌎 NA |
- For susceptible parasites: See package label for specific directions if giving by intraruminal injection.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For susceptible parasites | 3-4.5 mg/kg PO | PO | Single dose | — | 🌎 NA |
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For susceptible parasites | 5 mg/kg PO | PO | Single dose | — | 🌎 NA |
Goats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For susceptible parasites | 7.5 mg/kg PO | PO | Single dose | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Oxfendazole is a benzimidazole anthelmintic primarily indicated for use in cattle to remove and control lungworms, roundworms (including inhibited forms of Ostertagia ostertagi), and tapeworms.
- Broad-spectrum activity: Effective against a variety of pathogenic internal parasites.
- Extra-label use: Frequently utilized in horses, sheep, goats, swine, and dogs.
- Clinical Pearl: Oxfendazole is the active sulfoxide metabolite of fenbendazole. It offers improved gastrointestinal absorption compared to many other benzimidazoles, leading to higher plasma concentrations and longer resident times.
Mechanism of action
Oxfendazole exerts its antiparasitic effects by disrupting intracellular microtubular transport systems within the parasite.
- Binds selectively to and damages tubulin → prevents tubulin polymerization → inhibits microtubule formation.
- At higher concentrations, it disrupts metabolic pathways and inhibits key metabolic enzymes, including malate dehydrogenase and fumarate reductase, ultimately depleting the helminth's energy reserves and causing death.
Safety & warnings
Contraindications
- Female dairy cattle of breeding age
Adverse effects
- Hypersensitivity reactions (theoretically possible secondary to antigen release by dying parasites, particularly at high dosages)
Precautions
Warning: Not for use in female dairy cattle of breeding age. A 7-day slaughter withdrawal is required when using at labeled doses in cattle.
- Use cautiously in debilitated or sick horses.
- Hypersensitivity reactions may occur due to massive parasite die-off.
Drug interactions
Concurrent use is contraindicated; abortions in cattle and death in sheep have been reported after using these compounds together.
Monitoring
- Clinical efficacy (resolution of clinical signs, fecal egg counts)
Pharmacokinetics
Half-life
Absorption
Absorbed more readily from the GI tract compared to most other benzimidazole compounds. In dogs, peak levels occur at 8 hours post-administration.
Distribution
In dogs, oxfendazole plasma concentrations are significantly higher and resident times longer than that of either fenbendazole or albendazole following single oral administration.
Metabolism
Absorbed oxfendazole is metabolized (and vice-versa) to the active compound, fenbendazole (sulfoxide) and the sulfone.
Elimination
Elimination half-life is reported to be about 7.5 hours in sheep and 5.25 hours in goats.
Overdose
Safety Profile: Oxfendazole has a wide margin of safety.
Doses of 10 times those recommended elicited no adverse reactions in horses tested. It is highly unlikely that this compound would cause serious acute toxicity when given alone.
Available products
Formulations
- Oral Suspension 9.06%
- Oral Suspension 22.5%
Veterinary
- Oxfendazole Oral Suspension: 9.06% (Synanthic)
- Oxfendazole Oral Suspension: 22.5% (Synanthic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at room temperature and protect from light. Discard any unused suspension 24 hours after it has been reconstituted.
Client information
Important Safety Note: Do not use in horses intended for human consumption.
- Administration: Shake the oral suspension thoroughly before administering.
- Food Animal Restrictions: In cattle, a strict 7-day slaughter withdrawal is required. It is not FDA-approved for use in lactating dairy cattle.
- Side Effects: Adverse effects are extremely rare, but contact your veterinarian if your animal shows signs of an allergic reaction (e.g., facial swelling, hives, difficulty breathing) after administration.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.