Acetaminophen elimination kinetics in neonates, children, and adults.

The elimination of acetaminophen (APAP) following an oral dose of 10 mg/kg in newborn infants, children, and adults was compared. Urinary excretion of unchanged APAP, APAP-sulfate, and APAP-glucuronide was complete within 30 hr at all ages. Higher percentages of the dose were excreted in the urine as APAP-sulfate in neonates (0-2 days old) and children (3-9 yr old) than in 12-yr old children and adults. A pharmacokinetic analysis indicated that the higher rate of APAP-sulfate formation in younger age groups apparently compensated for a deficiency in glucuronide formation. No dramatic age-related differences in the overall elimination rate constant for APAP were observed despite the quantitative changes in the metabolic pathways during early childhood.