Studies on the mode of action of beclotiamine on Eimeria tenella.

The thiamine antagonist beclotiamine showed anticoccidial activity against Eimeria tenella, although metabolites and related substances were inactive. Oocyst production in experiments employing unilateral caecal ligation suggested that the drug reached parasitized cells by downward movement through the intestinal lumen, rather than by absorption and systemic transport. In chickens given 100 p.p.m. beclotiamine in the feed over a period of 7 days, duodenal drug concentrations of approximately 5.8 p.p.m. were achieved and maintained, while concentrations in the caeca were lower, but gradually increased to 1.2 p.p.m. Caecal levels were slow to fall following drug withdrawal, whereas duodenal levels showed an immediate decrease. [3H]thiamine absorption from the caeca of normal chicks or of chicks infected with E. tenella was inhibited by oral administration of beclotiamine. Pyrithiamine showed slight anticoccidial activity at 30 p.p.m. as did 2,4-dinitrophenol (2,4-DNP) at 100 p.p.m. A combination of 40 p.p.m. beclotiamine and 200 p.p.m. 2,4-DNP was quite effective although weight gains were not as good as with 120 p.p.m. beclotiamine alone.