Biotransformation of pethidine: a comparative study of 24 h urine in three ethnic groups

219 surgical patients of either Caucasian, Chinese or Nepalese origin were given pethidine 1 mg/kg by intramuscular injection as pre-operative medication. Urine was collected for 24 h and analysed for pethidine, pethidinic acid, pethidinic acid conjugates, norpethidine, norpethidinic acid, and norpethidinic acid conjugates. The mean proportion of the percentage of metabolites attributable to oxidative demethylation, hydrolysis and conjugation was almost identical in each ethic group (P > 0.2). It was concluded that there were no differences in the metabolic variability of the biotransformation of pethidine in Asians and Caucasians in whom the urine pH had not been acidified.