# Oxfendazole: veterinary dose and monograph

> Oxfendazole is a veterinary antiparasitic. A broad-spectrum benzimidazole anthelmintic (the active metabolite of fenbendazole, and itself reduced to fenbendazole — they interconvert) used for GI roundworms, lungworm and some tapeworm/inhibited larval stages in cattle, sheep… Indications include GI nematodes (Ostertagia, Haemonchus, Cooperia, Trichostrongylus, etc.); lungworm (Dictyocaulus); some tapeworm (Moniezia) and inhibited/larval stages. This monograph lists 6 reference doses for dogs, cattle, horses, goats, sheep and pigs, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/oxfendazole · Last reviewed: 2026-10-01

## 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

*Oxfendazole doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Oslerus osleri (tracheal worm) | 10 mg/kg | PO | q24h | 28 days |

- 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

*Oxfendazole doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| GI nematodes / lungworm | 4.5 mg/kg | PO | single dose | — | 7d slaughter |

- 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

*Oxfendazole doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GI nematodes | 10 mg/kg | PO | single dose | — |

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

### Goats

*Oxfendazole doses for goats*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| GI nematodes (off-label, higher dose) | 7.5 mg/kg | PO | single dose | — | Withdrawal NOT established — treat as extra-label |

- 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

*Oxfendazole doses for sheep*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| GI nematodes | 5 mg/kg | PO | single dose | — | Withdrawal NOT established — treat as extra-label |

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

### Pigs

*Oxfendazole doses for pigs*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| GI nematodes | 3–4.5 mg/kg | PO | single dose | — | Withdrawal NOT established — treat as extra-label |

- 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.

*Oxfendazole doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| GI nematodes / lungworm | 4.5 mg/kg | PO | single dose | — | 7d slaughter |

- 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

> **Caution:** 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

> **Caution:** 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

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- [Niclosamide](https://vetmasterji.com/drugs/niclosamide)
- [Nitenpyram](https://vetmasterji.com/drugs/nitenpyram)
- [Nitroxynil](https://vetmasterji.com/drugs/nitroxynil)
- [Oxibendazole](https://vetmasterji.com/drugs/oxibendazole)
- [Permethrin](https://vetmasterji.com/drugs/permethrin)
- [Piperazine](https://vetmasterji.com/drugs/piperazine)
- [Ponazuril](https://vetmasterji.com/drugs/ponazuril)

## Frequently asked questions

### What is the dose of Oxfendazole for dogs?

Reference doses for Oxfendazole in dogs: 10 mg/kg PO q24h for 28 days (Oslerus osleri (tracheal worm)). Confirm against the label and the patient before use.

### What is the dose of Oxfendazole for cattle?

Reference doses for Oxfendazole in cattle: 4.5 mg/kg PO single dose (GI nematodes / lungworm). Confirm against the label and the patient before use.

### What is the dose of Oxfendazole for horses?

Reference doses for Oxfendazole in horses: 10 mg/kg PO single dose (GI nematodes). Confirm against the label and the patient before use.

### What is the withdrawal period for Oxfendazole?

Cattle, PO (GI nematodes / lungworm): 7d slaughter; Goats, PO (GI nematodes (off-label, higher dose)): Withdrawal NOT established — treat as extra-label; Sheep, PO (GI nematodes): Withdrawal NOT established — treat as extra-label; Pigs, PO (GI nematodes): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Oxfendazole not be used?

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.

### What are the side effects of Oxfendazole in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.