2-Cyclohexylcarbonyl-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (praziquantel, EMBAY 8440, Biltricide) in single oral doses between 15 and 50 mg/kg given to subjects of all ages with Schistosoma haematobium infections produced few side effects even at the higher doses. Parasitological results were as follows: a) 15--20 mg/kg were too low to consistently give a favourable parasitological response. b) 21--25 mg/kg cured a high proportion of cases but because of poor response in some persons with high pretreatment egg loads, this dose range is not recommended. c) Doses of 45--50 mg/kg did not appear to improve efficacy when compared with 30--40 mg/kg. 2. Praziquantel was highly effective and had low toxicity in a controlled trial in schoolchildren. There was no significant difference in efficacy between two single dose regimens (30 and 40 mg/kg) and a split dose of 2x20 mg/kg given 4 h apart. In long-term follow-up examination no viable eggs were being excreted in 45 of 53 (84.9%) and 37 of 50 (74%) subjects examined 1 and 2 years, respectively, after treatment. 3. 16 persons excreting viable eggs 6 months after treatment were retreated with 35 mg/kg. Six months later 14 of the 16 (87.5%) were cured.
