Laboratory studies with some older anticoccidials.

Features of the anticoccidial activity of nicarbazin, amprolium, zoalene, sulphadimidine, diaveridine, Darvisul, spiramycin, chloramphenicol and oxytetracycline have been re-investigated both in vivo and in cell culture using Eimeria tenella. Of the drugs studied, only spiramycin was appreciably coccidiocidal, although nicarbazin and amprolium showed possibly slower coccidiocidal activity. In order to show activity against a particular stage in the life-cycle, higher concentrations of drug than those usually recommended for field usage had in most cases to be used. Under these conditions, parasites were usually inhibited as multinucleate 1st generation schizonts. With delayed medication, effects against 2nd generation parasites were in most cases found, and in many cases, although the parasites never matured to give viable merozoites, the large degenerating forms produced were able to cause extensive tissue destruction and haemorrhage. Methodology in this type of study is discussed in relation to more active and more recent anticoccidials, and some further experiments with robenidine reported.