Pharmacokinetics of oral diclofenac and acetaminophen in children after surgery

BACKGROUND: Our aim was to study the pharmacokinetics and pain scores following administration of single oral doses of either diclofenac or high-dose acetaminophen (paracetamol). METHODS: In the morning, the day after tonsillectomy, children 5-15 years of age were randomized in a double-blind manner to receive either diclofenac 1-2 mg.kg-1 (n=11) or acetaminophen 22.5 mg.kg-1 (n=10). Postoperative pain was assessed by self-report and blood samples were drawn every 30 min for 4 h after medication. RESULTS: Large interindividual differences in maximum plasma diclofenac concentrations (Cmax) were found. Mean Cmax was 2.4+/-1.3 microg.ml-1 and mean tmax was 2+/-0.5 h. No significant reduction in pain score with diclofenac was seen at any of the assessments during the study period. Eight of 10 children achieved Cmax of acetaminophen within the 10-20 microg.ml-1 antipyretic range. Mean tabs was 0.7+/-0.3 h and mean Cmax and tmax were 12.7+/-3.8 microg ml-1 and 1.4+/-0.5 h, respectively. No significant reduction in pain score with acetaminophen was seen at any of the assessments during the study period. CONCLUSIONS: The achieved concentrations of diclofenac and acetaminophen were not able to significantly reduce the children's pain score during the 5 h postingestion study period. Analgesic plasma acetaminophen concentrations may be higher than those required for antipyresis.