[The plasma levels of haloperidol and reduced haloperidol in Japanese psychiatric patients].

We measured plasma levels of haloperidol (HAL) and its metabolite, reduced haloperidol (RHAL), in 30 psychiatric patients receiving haloperidol. HAL and RHAL levels were measured by reversed-phase high-performance liquid chromatography. The results were as follows. (1) Plasma levels of HAL had a highly positive correlation with daily dose per body weight (r = 0.902). (2) Distribution of individuals in relation to RHAL levels appeared to have a bimodal pattern. Of these 30 patients studied, 7 were identified as extensive metabolizers (23%). (3) RHAL/HAL ratios showed small intra-individual variance, while inter-individually they varied largely. The mean RHAL/HAL ratio in 30 patients was 0.692; when the 7 extensive metabolizers were excluded, it was 0.491. (4) In the individuals with clinical improvements, plasma levels of HAL and RHAL were 7.45 +/- 4.46, 3.96 +/- 2.16 ng/ml (mean +/- SD), respectively. Patients showing high plasma levels of HAL and RHAL (greater than 30 ng/ml) became aggravated during HAL treatment.