Anticoccidial activity of 1-phenyluracils.

The minimum effective concentration (MEC) of 6-azauracil against Eimeria tenella when incorporated in feed is about 1000 ppm. Attachment of suitably substituted phenyl side chains at the 1-position reduces the MEC to less than 1 ppm. Uracil itself is devoid of anticoccidial activity, but side chains attached at the 1-position potentiate uracil and result in activity against E. tenella. Although effective at levels as low as 60 ppm, the 1-phenyluracils are less active than the corresponding 1-phenyl-6-azauracils. They also are less acidic.