Paracetamol metabolism after general anaesthesia.

Paracetamol metabolism was compared between nine patients after general anaesthesia and nine healthy volunteers. Each subject received 1.5 g of paracetamol orally, and paracetamol concentrations in venous blood were measured by HPLC at intervals over 12 h. Urine samples collected over 24 h were analysed by HPLC for cysteine, mercapturic acid, sulphate and glucuronide metabolites. There were no significant differences in the area under the concentration-time curve for paracetamol, or plasma half-life. Statistically significant differences were observed in the median percentages of unchanged paracetamol (volunteers 2.9%, patients 2.0%) and mercapturic acid (volunteers 4.5%, patients 6.5%) excreted in 24 h. The percentage of sulphate excreted was significantly lower in the 8-24-h period, although there was no difference over the total 24 h.