Amprolium: veterinary dose and monograph

At a glance

Drug class

Antiparasitic

Also known as

Amprol, Corid, Amprolium hydrochloride

Species with doses

Dogs, Cats, Cattle, Goats, Sheep, Pigs, Poultry and Camelids

General dose range

10–20 mg/kg PO q24h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Poultry coccidiosis (Eimeria spp.) — prevention and treatment
• Calf, lamb and kid coccidiosis
• Coccidiosis outbreaks in intensively reared birds/ruminants

Amprolium 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

• Coccidiosis (puppies): Plumb’s p.101 (Greene 2006): pups under 10 kg adult weight 100 mg, over 10 kg 200 mg (20% powder in a capsule) PO once daily for 7–12 days; or 250–300 mg on food; or 30 mL of 9.6% solution per gallon as the only water for 7–10 days. Papich 5e: 1.25 g of 20% powder in daily feed or 30 mL of 9.6% solution in 3.8 L water for 7 days.

Cats

• Coccidiosis (Cystoisospora): Plumb’s p.101 (Lappin 2000): 60–100 mg total PO once daily for 7 days; or 110–220 mg/kg on food for 7–12 days; with sulfadimethoxine 150 mg/kg amprolium + 25 mg/kg for 14 days (Greene 2006).

Cattle

• Calf coccidiosis (treatment): Papich 5e and Plumb’s p.101 (Todd 1986): 10 mg/kg PO once daily for 5 days. High doses or long courses can cause thiamine-deficiency polioencephalomalacia.
• Calf coccidiosis (prevention): Papich 5e and Plumb’s p.101: 5 mg/kg PO once daily for 21 days.

Goats

• Coccidiosis — goat kids: Plumb’s 10e p.85 (extra-label): goat kids — 50 mg/kg PO daily for 5 days effectively reduces faecal shedding of Eimeria oocysts without inducing neurologic disease. (The older Plumb’s gave only the lamb dose, 55 mg/kg daily for 19 days.) Amprolium is a thiamine antagonist — high doses or long courses can induce polioencephalomalacia. Obtain a FARAD withdrawal.

Sheep

• Coccidiosis (lambs): Plumb’s p.101 (Todd 1986): lambs 55 mg/kg PO daily for 19 days. Watch for polioencephalomalacia (thiamine antagonism). Obtain a withdrawal from the label or FARAD.

Pigs

• Coccidiosis: Plumb’s p.101 (Todd 1986): 25–65 mg/kg PO once or twice daily for 3–4 days; or 100 mg/kg/day in food or water (Howard 1986).

Poultry

• Coccidiosis treatment (water): Typically 0.012–0.024 % in drinking water (≈120–240 ppm) per label; convert to mg/kg by intake.

Buffalo

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

• Calf coccidiosis (treatment): Papich 5e and Plumb’s p.101 (Todd 1986): 10 mg/kg PO once daily for 5 days. High doses or long courses can cause thiamine-deficiency polioencephalomalacia.
• Calf coccidiosis (prevention): Papich 5e and Plumb’s p.101: 5 mg/kg PO once daily for 21 days.

Camelids

• Eimeria macusaniensis: Plumb’s p.101: 10 mg/kg PO once daily for 5 days (Wolff 2009), or for 10–15 days with thiamine 10 mg/kg SC every 5 days (Cebra 2007).

Contraindications

Prolonged high-dose use in ruminants (thiamine-deficiency PEM risk). Do not exceed labelled duration. Known hypersensitivity. Verify food-animal withdrawal/egg restrictions per product.

Species-specific warnings

Cattle: Excess/prolonged dosing causes thiamine-deficiency polioencephalomalacia — treat with parenteral thiamine and discontinue.

Goats: Goats/kids dosed off-label at the higher end are prone to PEM — monitor neurological status.

Adverse effects

• Thiamine deficiency / polioencephalomalacia with overdose or prolonged use (ruminants)
• Reduced feed/water intake if palatability is poor
• Generally very well tolerated at label doses

Drug interactions

• Supplemental thiamine (B1) antagonises the anticoccidial effect — avoid high B-vitamin supplementation during treatment
• Other thiamine antagonists (e.g. excess sulphur in ruminant diets): additive PEM risk

Pregnancy and lactation

Considered safe at label doses in breeding/pregnant food animals; widely used in young stock.

Monitoring

• Faecal oocyst counts / clinical response
• Neurological signs (PEM) on prolonged or high-dose courses in ruminants
• Water/feed intake (palatability)
• Adherence to label duration

Toxicity and overdose

Overdose or prolonged courses cause thiamine-responsive polioencephalomalacia — blindness, head-pressing, opisthotonus, seizures (especially in ruminants). Birds tolerate it well within label limits. Otherwise low acute toxicity.

Management: Stop amprolium and give parenteral thiamine (vitamin B1) promptly — 10–20 mg/kg thiamine for ruminant PEM, repeated as needed — plus supportive/anticonvulsant care. Neurological signs reverse if treated early.

Clinical pearls

• Keep an eye on the thiamine angle: too much amprolium for too long causes the very brain disease (PEM) you must reverse with B1
• Do not co-supplement high-dose thiamine during treatment — it cancels the anticoccidial action
• Water medication must be made fresh daily and be the only water source for reliable intake
• For ruminant PEM from any cause, amprolium overdose is a classic differential — ask about recent coccidiosis treatment

Mechanism of action

A structural analogue of thiamine (vitamin B1). It competitively blocks thiamine uptake/transport in Eimeria, depriving the parasite (which has a high thiamine requirement during first-generation schizogony) of an essential cofactor and halting its development. The same antagonism, if excessive, can deplete host thiamine and precipitate cerebrocortical necrosis (PEM).

Formulations and products

• Soluble powder 20 % (water-medication)
• Oral solution 9.6 % (96 mg/mL)
• Feed premix
• Amprolium 20 % soluble powder (Various (India)) — 200 mg/g, Soluble powder (water)
• Corid (Amprol) 9.6 % oral solution (Huvepharma / MSD) — 9.6 % (96 mg/mL), Oral solution
• Corid 20 % soluble powder (Huvepharma / MSD) — 20 % (200 mg/g), Soluble powder (water medication)

Storage

Powders/solutions: 15–30 °C, dry, protected from light. Medicated water: prepare fresh daily.

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.

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Frequently asked questions