Tolerance of Kenyan Schistosoma mansoni to oxamniquine

Although 30 mg/kg oxamniquine produced high levels (85·5 to 99·5%) of egg reduction in Kenyan children infected with Schistosoma mansoni after a single oral treatment, cure rates from children at Mwea in Kirinyaga district were lower than those from Machakos (58% v. 74%). Redosing uncured children confirmed this lower cure rate (36% v. 83%). Isolates from infected children were passaged into mice and dosed with oxamniquine. Lower than expected reductions in worm numbers were obtained, suggesting that oxamniquine tolerant S. mansoni are present in the normal worm population in Kenya. It is concluded that mass use of oxamniquine at 30 mg/kg may produce problems of drug resistance.