Amprolium — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Cattle	PO (oral drench, feed, or water)	10 mg/kg for treatment; 5 mg/kg for prevention	Once daily	Duration: 5 days for treatment; 21 days for prevention Notes: For treatment, administer as a drench or in feed/water. For prevention, provide continuously in feed or water.
Sheep and Goats	PO (oral drench, feed, or water)	10 mg/kg for treatment; 5 mg/kg for prevention	Once daily	Duration: 5 days for treatment; 21 days for prevention Notes: Same as cattle; ensure adequate intake if administered in water.
Poultry (Chickens, Turkeys)	PO (feed or water)	0.0125% in feed (0.0125% amprolium) for prevention; 0.025% in feed for treatment	Continuous administration	Duration: Prevention: throughout risk period; Treatment: 3-5 days Notes: For water administration, use 0.024% solution for 3-5 days. Do not use in layers producing eggs for human consumption.
Rabbits	PO (water or feed)	0.02% in drinking water	Continuous	Duration: 5 days Notes: Ensure fresh solution daily. For severe outbreaks, may increase to 0.04% for 5 days.

Clinical Indications & Species Uses

General Indications

Prevention and treatment of coccidiosis in food-producing animals and poultry.

Cattle (Bovine)

Prevention and treatment of coccidiosis caused by Eimeria bovis and Eimeria zuernii.

Small Ruminants (Sheep / Goat)

Prevention and treatment of coccidiosis in sheep and goats caused by Eimeria species.

Rabbit & Small Mammals

Prevention and treatment of hepatic and intestinal coccidiosis caused by Eimeria species.

Avian & Poultry

Prevention and treatment of coccidiosis in chickens and turkeys caused by Eimeria species.

Exotic & Other Species

Occasionally used in other avian species and some exotic animals for coccidiosis, but not FDA-approved.

Pharmacology & Mechanism of Action

Drug Class: Coccidiostat | Pharmacological Group: Thiamine (Vitamin B1) Antagonist

Mechanism of Action: Amprolium is a structural analog of thiamine (vitamin B1) that competitively inhibits the uptake of thiamine by coccidial parasites. Since coccidia are unable to synthesize thiamine de novo, they depend on active transport from the host's intestinal lumen. Amprolium blocks this transport, leading to a deficiency of thiamine within the parasite, which disrupts carbohydrate metabolism and energy production, ultimately causing parasite death. The drug is most effective against the first-generation schizonts (asexual stages) of Eimeria species, thereby preventing the development of clinical coccidiosis.

Pharmacodynamics: Amprolium exhibits coccidiostatic activity against a broad spectrum of Eimeria species in poultry and livestock. It acts primarily on the asexual stages of the parasite's life cycle, particularly the first-generation schizonts, reducing oocyst shedding and preventing mucosal damage. The drug has a wide margin of safety in target species, but its efficacy is dose-dependent and may be reduced in the presence of high dietary thiamine. It does not possess antibacterial or antifungal activity.

⚡ Pharmacokinetics Summary

Absorption: Amprolium is poorly absorbed from the gastrointestinal tract, with systemic absorption typically less than 10% in most species. The majority of the drug remains in the intestinal lumen, which is the desired site of action for coccidial control. In poultry, oral administration results in high concentrations in the ceca and small intestine.

Distribution: Due to poor absorption, systemic distribution is minimal. The small amount that is absorbed is widely distributed in tissues, but concentrations are low. It does not cross the blood-brain barrier to a significant extent.

Metabolism: Amprolium is minimally metabolized in the body. The absorbed fraction is primarily excreted unchanged. Some metabolism may occur in the liver, but the extent is negligible.

Excretion: The primary route of excretion is via the feces, as the majority of the drug is not absorbed and passes through the gastrointestinal tract. The small absorbed fraction is excreted in the urine. In poultry, elimination is rapid, with most of the drug excreted within 24-48 hours after administration.

Half-Life: The half-life in most species is short, approximately 2-4 hours in poultry and ruminants, due to rapid excretion.

Bioavailability: Oral bioavailability is low (<10%) due to poor absorption, which is intentional for local action in the gut.

Protein Binding: Protein binding is low, estimated at less than 20%.

Available Formulations & Strengths

Oral Powder (for feed or water) Various concentrations, e.g., 25%, 50% (PO)

Oral Solution (for drinking water) 9.6% (as amprolium solution) (PO)

Premix (for feed) Various, e.g., 25% (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to amprolium
Do not use in animals with thiamine deficiency or those on thiamine-deficient diets
Do not use in lactating dairy cattle (unless specifically approved) due to milk withdrawal
Do not use in layers producing eggs for human consumption (in poultry)

Warnings & Clinical Precautions:

Use with caution in animals with liver or kidney disease
Ensure adequate thiamine intake in the diet to avoid deficiency
In poultry, do not use in birds producing eggs for human consumption
For food animals, observe withdrawal times
Avoid contamination of feed and water with other drugs
Use only as directed; overdosing may cause thiamine deficiency symptoms

Adverse Effects & Reactions

Common:

Mild gastrointestinal upset (diarrhea, anorexia) at high doses
Reduced feed intake in poultry

Serious / Severe:

Thiamine deficiency (polyneuritis, opisthotonos) with prolonged high doses
Neurological signs in severe cases

Rare:

Allergic reactions
Hepatotoxicity (rare)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Thiamine (Vitamin B1)	Thiamine supplementation may reduce the efficacy of amprolium by competing for uptake.	Moderate
Other coccidiostats (e.g., monensin, lasalocid)	Potential additive effects or toxicity; avoid concurrent use unless directed by a veterinarian.	High
Sulfonamides	May have synergistic effects against coccidia, but may increase risk of adverse effects.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Thiamine deficiency signs: ataxia, opisthotonos, convulsions
Anorexia
Diarrhea
Weight loss
In severe cases, death

Emergency Treatment Protocol: Discontinue amprolium immediately. Administer thiamine (vitamin B1) parenterally or orally to reverse toxicity. Provide supportive care including fluids and nutritional support. In poultry, thiamine can be added to drinking water.

Food Animal Withdrawal Times

🥩 Meat: 1 days🥛 Milk: 0 days🥚 Eggs: 0 days

Withdrawal times vary by country and formulation. In the US, for cattle, the withdrawal period is 1 day for meat and 0 days for milk when used according to label. For poultry, withdrawal is 1 day for meat; eggs are not allowed if used in layers. Always follow local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (15-30°C) in a dry place.

Handling & Special Conditions: Keep container tightly closed. Protect from moisture. Store away from feed and food items.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Approved for use in poultry and cattle in the US. Some formulations are available over-the-counter.

Extra-Label (Off-Label) Use: Extra-label use in food animals requires a valid veterinary-client-patient relationship and must comply with AMDUCA regulations. Withdrawal times must be extended if used off-label.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Amprolium is a widely used coccidiostat in poultry and livestock. It is most effective when used as a preventive measure during periods of high risk, such as in young animals or during stressful conditions. For treatment of active coccidiosis, higher doses are used for a short duration. It is important to ensure that animals have access to adequate thiamine in their diet to prevent deficiency. In poultry, amprolium is often used in starter feeds and can be rotated with other coccidiostats to reduce resistance development. In cattle and sheep, it is commonly used in feed or water during outbreaks. Always follow label instructions and observe withdrawal times for food animals.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)