Description: It is quarternized derivative of pyrimidine which is a thiamine antagonist. It is most active against E. tenella, E. necatrix and E. acervulina and to lesser extent E. maxima. It could be fed at several times the recommended dose with no ill effects and probably, one of the safest anti-coccidial drugs to be used extensively. There is no premarketing withdrawal requirement for this compound.

Dosage: 125 ppm; . Amprolium is the only active pharmaceutical ingredient approved for prevention and treatment in laying chicken.

Mode of Action: It is thiamine antagonist and due to its close structural similarity it blocks the thiamine receptors. This blockage of receptors prevents coccidia from utilizing thiamine and as a result thiamine is unavailable to coccidian (Competitive inhibition of thiamine uptake). This vitamin (thiamine pyrophosphate) is a cofactor of several decarboxylase enzymes which play role in cofactor synthesis. It is only agent which can be used in laying birds both for prevention and treatment of outbreaks. At higher doses, thiamine deficiency can occur in host but it can be prevented by addition of thiamine.

Stage of the life cycle affected by the drug: It is effective against 1st generation of trophozoites and schizonts and shows peak activity early in day 3 of cycle. It also suppresses the sexual stages, gametogony and sporulation of oocyst. 

Pharmacokinetics: Rapidly eliminated (within few hours) from the body via kidneys.

Toxicity: Chicken LD50 5.1 g/kg (single oral dose). Wide margin of safety.

Drug combinations: Combination of amprolium with ethopabate, sulphaquinoxaline or even pyrimethamine extended and strengthened the spectrum of activity. Amprolium is compatible with vitamins, antibiotics, minerals and other ingredients commonly used in poultry ration but it should not be mixed in concentrates containing high levels of choline because of tendency for it to break down into picric acid.

Residues: Amprolium may be found in eggs up to 10 days after withdrawal from the feed. No withdrawal time has been assigned for eggs (No MRL).

Resistance: Continuous use of Amprolium is resulting into the development of drug resistance which is a major problem and limiting its use.