After a single oral dose of praziquantel with 250 ml of grapefruit juice, the area under the concentration-time curve and the maximum concentration in plasma of praziquantel (Cmax) were significantly increased (Cmax for water treatment, 637.71 +/- 128.5 ng/ml; and Cmax for grapefruit juice treatment, 1,037.65 +/- 305.7 ng/ml, P < 0.05). No statistically significant differences were found in the time to maximum concentration of drug in plasma or elimination half-life.