Urinary propofol metabolites in early life after single intravenous bolus

Propofol clearance is lower in neonates than in adults and displays extensive interindividual variability, in part explained by postmenstrual age (PMA) and postnatal age (PNA). Since propofol is almost exclusively cleared metabolically, urinary propofol metabolites were determined in early life and compared with similar observations reported in adults. Twenty-four hours urine collections were sampled after a single i.v. bolus of propofol (3 mg kg(-1)) in neonates undergoing procedural sedation. Clinical characteristics (PMA, PNA, weight, and cardiopathy) were recorded. Urine metabolites [propofol glucuronide (PG), 1- and 4-quinol glucuronide (QG)] were quantified using high-pressure liquid chromatography. Urine recovery (% administered dose) and the contribution of PG and QG to urinary elimination were calculated. Data were reported by median and range, analysed by Mann-Whitney U or Spearman's rank. Eleven neonates (median PNA 11 days, PMA 38 weeks) were included. Median propofol metabolite recovery was 64% (range 34-98%). PG contributed 34% (range 8-67%) and QG 65% (range 33-92%). There was no significant correlation between either PMA, PNA, or cardiopathy and propofol metabolites. Compared with adults, the contribution of PG (34% vs 77%) was lower and the contribution of QG (65% vs 22%) was higher in neonates. Propofol metabolism in neonates differs from adults, reflecting the age-dependent limited glucuronidation capacity. Hydroxylation to quinol metabolites already contributes to propofol metabolism. These differences likely explain the PMA- and PNA-dependent reduced propofol clearance in neonates.