The present study was undertaken to determine the acceptablility, tolerance and effectiveness of praziquantel in a rural population infected with Clonorchis sinensis and to suggest the suitable dosages of praziquantel for the field use on a large scale. A total of 121 patients with proven C. sinensis infection were treated by two dosages with praziquantel at a single dose of 40 mg/kg bwt and 2 doses of 30 mg/kg bwt in a single day. A single dose of 40 mg/kg bwt were given to 60 patients and 2 x 30mg/kg bwt were given to 61 patients. Follow-up examinations were carried out at about 30 and 60 days after treatment. Two months after therapy, 13(21.7%) of 60 patients who received a single dose of 40 mg/kg bwt were cured completely. Among these cured patients, 9(75.0%) out of 12 cases of light and only 4 out of 48 cases of moderate or heavy infection groups were cured. But in the non-cured cases the overall egg reduction rate was 89.1%. On the other hand, 36(59.0%) out of 61 patients treated with 2 x 30mg/kg bwt were cured at 60 days after treatment. Among these cured patients, all of the 13 cases of light infection and 18(69.2%) out of 26 cases of moderate and 5(23.8%) out of 21 cases of heavy infection groups were cured completely at 60 days after therapy. However the overall egg reduction rate was 95.2% in the non-cured cases. Praziquantel is well tolerated and side effects consist particularly of mild and transient headache, dizziness and abdominal discomfort, etc. However there was no difference in regard to frequency and intensity of untoward side effects between the two dosage groups. The results obtained in this study suggest that a single dose of 40 mg/kg bwt for light infection, 2 x 30mg/kg bwt for moderate infection and 3 x 25mg/kg bwt for heavy infection groups will be recommended for the field use on a large scale.
