Oxfendazole: veterinary dose and monograph

At a glance

Drug class

Antiparasitic

Also known as

Synanthic, Systamex, Oxfen

Species with doses

Dogs, Cattle, Horses, Goats, Sheep and Pigs

General dose range

4.5–10 mg/kg PO single dose (repeat per cycle) — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• GI nematodes (Ostertagia, Haemonchus, Cooperia, Trichostrongylus, etc.)
• Lungworm (Dictyocaulus)
• Some tapeworm (Moniezia) and inhibited/larval stages
• Routine strategic deworming in ruminants/horses/pigs

Oxfendazole dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Oslerus osleri (tracheal worm): Plumb’s p.917 (Bowman 2006): 10 mg/kg PO once daily for 28 days. Papich 5e: dose otherwise not established in dogs.

Cattle

• GI nematodes / lungworm: Papich 5e and Plumb’s p.917 (Synanthic label): 4.5 mg/kg PO or by intraruminal injection (22.5% only); may repeat in 4–6 weeks. 9.06%: 2.5 mL per 100 lb; 22.5%: 1 mL per 100 lb. US slaughter withdrawal 7 days; not for lactating dairy cattle.

Horses

• GI nematodes: Papich 5e and Plumb’s p.917 (label): 10 mg/kg PO.

Goats

• GI nematodes (off-label, higher dose): Plumb’s p.917 (Roberson 1988): goats 7.5 mg/kg PO. Extra-label — obtain a FARAD withdrawal.

Sheep

• GI nematodes: Plumb’s p.917 (Brander; Roberson): sheep 5 mg/kg PO. Follow the local product-label withdrawal. Check flock benzimidazole resistance.

Pigs

• GI nematodes: Plumb’s p.917 (Roberson 1988): swine 3–4.5 mg/kg PO. Follow the product-label withdrawal.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• GI nematodes / lungworm: Papich 5e and Plumb’s p.917 (Synanthic label): 4.5 mg/kg PO or by intraruminal injection (22.5% only); may repeat in 4–6 weeks. 9.06%: 2.5 mL per 100 lb; 22.5%: 1 mL per 100 lb. US slaughter withdrawal 7 days; not for lactating dairy cattle.

Contraindications

Early pregnancy at high/repeated doses (theoretical benzimidazole teratogenicity at high doses — follow label). Known hypersensitivity. Observe food-animal withdrawal. Confirm benzimidazole susceptibility where resistance is suspected.

Species-specific warnings

Goats: Off-label in goats — higher dose needed and withdrawal not established; extend meat/milk withdrawal conservatively.

Adverse effects

• Mild, transient GI effects (uncommon)
• Very well tolerated — wide safety margin
• Reduced efficacy where benzimidazole resistance exists

Drug interactions

• No major systemic drug interactions
• Cross-resistance with other benzimidazoles (fenbendazole, albendazole, etc.)

Pregnancy and lactation

Benzimidazoles are generally regarded as safe in pregnancy at label doses; avoid very high/repeated dosing in early gestation.

Monitoring

• Faecal egg count reduction (efficacy AND resistance surveillance)
• Withdrawal-period compliance
• Rotate anthelmintic classes to slow resistance

Toxicity and overdose

Very wide safety margin; overdose typically causes only mild GI upset. High-dose/prolonged benzimidazole exposure can rarely affect rapidly dividing tissues (marrow), but this is not expected at deworming doses.

Management: Supportive — fluids if needed. No specific antidote required (wide margin).

Clinical pearls

• A broad-spectrum benzimidazole interchangeable in spectrum with fenbendazole (they interconvert) — good for GI worms, lungworm and inhibited larvae
• Benzimidazole resistance is common in small-ruminant worms — do faecal egg count reduction tests and rotate classes
• Goats need a higher mg/kg than sheep/cattle (faster metabolism) with no set withdrawal — extend conservatively
• Wide safety margin makes it forgiving, but still dose to accurate body weight

Mechanism of action

Binds parasite β-tubulin and inhibits microtubule polymerisation, disrupting the worm's cytoskeleton, nutrient uptake and energy metabolism — leading to parasite death. Mammalian tubulin has much lower affinity, giving the wide safety margin. Oxfendazole and fenbendazole interconvert in vivo (oxfendazole is the sulphoxide), so they share spectrum and resistance.

Formulations and products

• Oral suspension 22.65 mg/mL (2.265 %)
• Oral suspension 90.6 mg/mL (9.06 %)
• Intraruminal bolus / paste
• Synanthic (Boehringer Ingelheim) — 2.265 % / 9.06 % oral suspension, Oral drench
• Oxfen / Systamex (Various (India)) — Oxfendazole suspension/bolus, Suspension / bolus

Storage

Suspension/bolus: 15–30 °C, protect from light; shake suspension well.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antiparasitics

• Nicarbazin
• Niclosamide
• Nitenpyram
• Nitroxynil
• Oxibendazole
• Permethrin
• Piperazine
• Ponazuril

Frequently asked questions