Ethnic comparison of haloperidol and reduced haloperidol plasma levels: Taiwan Chinese versus American non-Chinese.

Steady-state haloperidol (HAL) and reduced HAL (RHAL) plasma levels were measured in Chinese and non-Chinese schizophrenic patients. The patients (n = 38) were matched according to age (+/- 1 yr) and by HAL dose. In general, Chinese patients had higher mean plasma HAL levels and lower RHAL/HAL ratios compared to non-Chinese patients (23.6 +/- 14.9 ng/ml versus 17.1 +/- 10.1 ng/ml, p less than 0.05; 0.52 +/- 0.44 versus 0.82 +/- 0.62, p less than 0.05). Six groups were formed according to HAL dose (number per group): 10 mg/day (6); 20 (11); 30 (11); 40 (4); 50 (3); and 60 (3). No significant differences were found in age, weight and dose/weight. In each dose group, HAL plasma levels were generally higher in the Chinese patients than in the non-Chinese patients, though significance was only detected in the 30 mg group (26.1 +/- 7.0 ng/ml versus 18.5 +/- 5.1 ng/ml, p = 0.035) and a slight trend in the 40 mg group (36.0 +/- 15.0 ng/ml versus 23.5 +/- 10.4 ng/ml, p = 0.074). RHAL/HAL ratios were generally lower in the Chinese patients than in the non-Chinese patients, with a strong trend toward the significance level in the 20 mg and 30 mg groups (0.22 +/- 0.13 versus 0.58 +/- 0.57, p = 0.066 and 0.43 +/- 0.26 versus 0.71 +/- 0.34, p = 0.062). This study further suggests the possibility of different metabolic rates between Chinese and non-Chinese patients. Possible differences in the enzyme systems which relate to the metabolism of HAL and RHAL between Chinese and non-Chinese populations are discussed.