Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Overview
Amprolium is an anticoccidial agent used in dogs and cats for the treatment of coccidiosis on an extra-label basis. It is a structural analogue of thiamine (vitamin B1) and functions primarily as a coccidiostat rather than a coccidiocidal drug, meaning it inhibits parasite development rather than directly killing the organism.
In small animal practice, amprolium is administered orally for the management of coccidial infections, particularly in puppies and kittens. Treatment duration is typically limited, as prolonged or high-dose therapy may interfere with thiamine metabolism and increase the risk of adverse neurologic effects. Palatability can be a limiting factor, especially when administered in drinking water.
Mechanism of Action (MOA): Amprolium competitively inhibits thiamine uptake by coccidial organisms by mimicking the structure of thiamine. This preferentially disrupts thiamine-dependent metabolic pathways within the parasite, impairing its development and replication. Although amprolium can also affect thiamine utilization in the host, this effect is significantly less pronounced when the drug is used at appropriate doses and for limited treatment durations.
Indications
In dogs and cats, amprolium is used on an extra-label basis for the treatment of coccidiosis caused by susceptible Eimeria species. Its use is most common in young animals, where clinical disease is more likely to occur, and in environments with increased exposure risk.
- Coccidiosis in dogs: Used for the management of intestinal coccidial infections, particularly in puppies, to reduce clinical signs and oocyst shedding.
- Coccidiosis in cats: Used for treatment of feline coccidiosis, especially in kittens, when clinical signs such as diarrhea or poor growth are present.
- Control of outbreaks: May be used in group-housed dogs or cats as part of outbreak control programs, provided adequate access to medicated water or food can be ensured.
Dosage (Reference)
Dog
In dogs, amprolium is used orally on an extra-label basis for the treatment of coccidiosis. Doses are expressed as a fixed amount per dog rather than on a mg/kg basis for most protocols. Treatment duration is typically limited to reduce the risk of thiamine deficiency.
| Clinical use | Route | Dose | Notes |
|---|---|---|---|
| Coccidiosis (20% powder – capsules) | PO |
Small dogs (<10 kg): 60–100 mg/dog once daily Large dogs (>10 kg): |
Dose is NOT mg/kg. Given for 7–12 days using gelatin capsules. |
| Coccidiosis (20% powder – in food) | PO | 250–300 mg/dog once daily | Mixed with food; commonly used for pups or nursing bitches. |
| Coccidiosis (9.6% oral solution – in water) | PO (drinking water) |
30 mL per 3.8 L (1 gallon) water OR 22.5 mL per 3.8 L water |
Treated water must be the sole source for 7–10 days; do not exceed 10 days. |
| Combination therapy | PO | 150 mg/kg once daily | Used in combination with sulfadimethoxine 25 mg/kg PO every 24 hours for 14 days. |
• Most protocols use fixed mg per dog, not mg/kg.
• Treatment duration should generally not exceed 12–14 days.
• Monitor water intake when using medicated water due to poor palatability.
• High doses or prolonged use increase risk of thiamine deficiency.
Cat
In cats, amprolium is used orally on an extra-label basis for the treatment of coccidiosis. Similar to dogs, dosing is typically based on a fixed amount per cat rather than body weight.
| Clinical use | Route | Dose | Notes |
|---|---|---|---|
| Coccidiosis (20% powder) | PO | 60–100 mg/cat once daily | Dose is NOT mg/kg; given for 7 days. |
| Coccidiosis (9.6% oral solution – in water) | PO (drinking water) | 7.5 mL per 3.8 L (1 gallon) water | Treated water used as sole source for 10 days. |
| Combination therapy | PO | 150 mg/kg once daily | Used with sulfadimethoxine 25 mg/kg PO every 24 hours for 14 days. |
• Fixed-dose regimens are commonly used rather than weight-based dosing.
• Ensure adequate water intake if using medicated water.
• Avoid prolonged treatment to reduce the risk of thiamine deficiency.
• Monitor for neurologic signs during therapy.
Warnings & Precautions
Amprolium should be used cautiously in dogs and cats, with particular attention to treatment duration and dosing accuracy. Most precautions relate to its interference with thiamine metabolism and the potential for neurologic toxicity when used improperly.
- Treatment duration: Prolonged administration or repeated courses increase the risk of thiamine deficiency; therapy is generally limited and should not be extended unnecessarily.
- Thiamine deficiency risk: As a thiamine analogue, amprolium can interfere with host thiamine utilization at high doses or with long-term use, potentially leading to neurologic complications.
- Use in puppies: Extended use is not recommended in puppies; shorter treatment courses are preferred to minimize neurologic risk.
- Palatability concerns: Liquid formulations may be bitter and poorly accepted, especially when administered in drinking water; inadequate intake can reduce treatment effectiveness.
- Dietary thiamine: Excessive dietary or supplemental thiamine may reduce or reverse the anticoccidial efficacy of amprolium.
- Monitoring during therapy: Dogs and cats receiving higher doses or combination protocols should be observed closely for early signs of neurologic dysfunction.
Drug Interactions
Drug interactions associated with amprolium in dogs and cats are limited and primarily related to its mechanism as a thiamine analogue. Most interactions involve reduced efficacy of amprolium rather than increased toxicity.
- Thiamine (vitamin B1): High levels of exogenously administered thiamine may reduce or reverse the anticoccidial activity of amprolium by competing for the same metabolic pathways.
Side Effects & Overdose
Side Effects
Adverse effects associated with amprolium in dogs and cats are uncommon and are most often related to dose or duration of therapy. When used appropriately and for limited treatment periods, the drug is generally well tolerated.
- Gastrointestinal effects: Anorexia, diarrhea, or mild gastrointestinal upset may occur, particularly during oral administration.
- Neurologic disturbances: Rarely reported signs include ataxia, circling, depression, central blindness, opisthotonos, and abnormal posturing (eg, “stargazing”). These effects are typically dose related.
- Thiamine deficiency–related signs: High doses or prolonged administration may interfere with thiamine metabolism, leading to neurologic dysfunction consistent with thiamine deficiency.
Overdose
Overdose or excessive duration of amprolium therapy in dogs and cats can result in significant neurologic toxicity, primarily due to functional thiamine deficiency.
- Neurologic signs: Ataxia, circling, central blindness, opisthotonos, and abnormal behavior may develop following excessive dosing.
- Management: Discontinue amprolium immediately and administer parenteral thiamine (vitamin B1). Supportive care and close neurologic monitoring are recommended.
Key Notes
Practical clinical points to guide appropriate use of amprolium in dogs and cats without repeating previously stated precautions or adverse effects:
- Coccidiostatic action: Amprolium suppresses coccidial development rather than directly eliminating organisms, so clinical improvement may be gradual.
- Best suited for young animals: Most commonly used in puppies and kittens, where coccidial infections are more likely to be clinically significant.
- Administration planning: Successful therapy depends on consistent daily intake; ensure accurate dosing when using capsules, food, or medicated water.
- Environmental control: Drug therapy should be combined with proper hygiene and sanitation to reduce reinfection and environmental contamination.
- Role in treatment protocols: May be used alone or as part of combination protocols for coccidiosis, depending on disease severity and clinical response.
- Reassessment after treatment: Clinical response should be evaluated at the end of therapy to determine if additional treatment or alternative agents are needed.
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