However, factors such as differences in age and weights of the study participants (mostly children), food effect, intestinal diseases, and a wide spectrum of CYP450 metabolizing enzymes involved in biotransformation of praziquantel (extensive first pass effect), including CYP3A, CYP1A2, CYP2C9 and CYP2C19 have been speculated12,19. The gene discussed is CYP2C19; the disease is intestinal disorder.