Amprolium
Amprolium is a widely used **anticoccidial** agent, structurally analogous to thiamine (Vitamin B1). While FDA-approved primarily for poultry and cattle to treat and prevent *Eimeria* infections, it is frequently used off-label in companion animals, small mammals, and exotics to treat coccidiosis (e.g., *Cystoisospora* spp. in dogs and cats). **Clinical Pearls:** * Because it acts as a thiamine competitive inhibitor, its safety margin is generally wide for short courses, but prolonged use can precipitate thiamine deficiency (polioencephalomalacia in ruminants or neurologic signs in small animals). * Treatment courses typically should not exceed 12-14 days. * The liquid formulation is notoriously bitter; when administered via drinking water, patients must be monitored closely to ensure adequate hydration.
Mechanism: Amprolium is a **thiamine (Vitamin B1) analog**. It competitively inhibits the active transport and utilization of thiamine by the parasite. * **Mechanism:** Amprolium โ blocks thiamine uptake โ disrupts carbohydrate metabolism in the parasite (specifically inhibiting **thiamine pyrophosphate (TPP)**-dependent enzymes) โ parasite death. * It primarily targets the **first-generation schizont** in the cells of the intestinal wall, preventing differentiation into merozoites. It may also suppress the sexual stages and sporulation of oocysts. * Because the host's thiamine transport mechanisms have a lower affinity for amprolium than the parasite's, toxicity to the host is minimized during short-term therapy.
Dosing by species
- Coccidiosis (Lambs) ยท 55 mg/kg daily ยท PO ยท q24h ยท 19 days
- Eimeria macusaniensis (Camelids - New World) ยท 10 mg/kg ยท PO ยท q24h ยท 5 days ยท Dosed for camelids
- Eimeria macusaniensis (Camelids - New World) ยท 10 mg/kg as a 1.5% solution ยท PO ยท q24h ยท 10-15 days ยท Give thiamine at 10 mg/kg SC once daily every 5 days during treatment. Dosed for camelids.
- Coccidiosis (Small Pups < 10 kg adult weight) ยท 100 mg (total dose) ยท PO ยท q24h ยท 7-12 days ยท Using the 20% powder in a gelatin capsule
- Coccidiosis (Large Pups > 10 kg adult weight) ยท 200 mg (total dose) ยท PO ยท q24h ยท 7-12 days ยท Using the 20% powder in a gelatin capsule
- Coccidiosis (Pups or bitches, in food) ยท 250-300 mg total dose ยท PO ยท q24h ยท 7-12 days ยท Using the 20% powder on food
- Coccidiosis (Pups or bitches, in water) ยท 30 mL of the 9.6% solution in one gallon of water ยท PO ยท ad libitum ยท 7-10 days ยท No other water provided
- Prophylaxis ยท 0.075% solution as drinking water ยท PO ยท ad libitum
- Coccidiosis (Combination therapy) ยท 150 mg/kg of amprolium and 25 mg/kg of sulfadimethoxine ยท PO ยท q24h ยท 14 days
- Control of coccidiosis ยท 1.5 tablespoonsful (22.5 mL) of the 9.6% solution per one gallon of water ยท PO ยท ad libitum ยท Not to exceed 10 days ยท Sole drinking water source. Monitor water consumption; rarely some dogs may not drink due to bitter taste.
Routes of administration
Contraindications
- Prolonged use (>12-14 days) especially in puppies
- Concurrent high-dose thiamine supplementation (reduces efficacy)
Adverse effects
- Neurologic disturbances (rare, dose-related)
- Depression
- Anorexia
- Diarrhea
- Thiamine deficiency (polioencephalomalacia) with prolonged high doses
Drug interactions
- Thiamine ยท Exogenously administered thiamine in high doses may reverse or reduce the anticoccidial efficacy of amprolium.
- Thiamine (Vitamin B1) ยท Exogenously administered thiamine may reduce the efficacy of amprolium. ยท major
Monitoring
- Clinical efficacy (resolution of diarrhea, negative fecal floats)
- Hydration status (especially if administered in drinking water)
- Neurologic signs (ataxia, depression) indicating potential thiamine deficiency
Overdose
Amprolium has induced **polioencephalomalacia (PEM)** in sheep when administered at 880 mg/kg PO for 4-6 weeks and at 1 gram/kg for 3-5 weeks. Erythrocyte production also ceased in lambs receiving these high dosages. In dogs, overdoses of amprolium will produce neurologic clinical signs. **Treatment:** * Discontinue amprolium therapy immediately. * Administer parenteral thiamine (1-10 mg/day IM or IV).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.