Figure 1.

a) Relationship between oral clearance of clozapine in the control phase and mean value of three paraxanthine/caffeine ratios in the caffeine phase in 12 non-smoking healthy volunteers who were given a single dose of 12.5 mg clozapine in each phase. A significant positive correlation was revealed (r_s = 0.62;/P = 0.03). b) Relationship between the desmethyl-clozapine AUC(0,12h)/clozapine AUC(0,12h) ratio in the control phase and mean value of three paraxanthine/caffeine ratios in the caffeine phase. A significant positive correlation was revealed (r_s = 0.77, P = 0.003).