Randomized controlled trial of duration of analgesia following intravenous or rectal acetaminophen after adenotonsillectomy in children.

Background: Doses of acetaminophen 40 mg kg(-1) rectally and 15 mg kg(-1) i.v. produce similar effect-site concentrations. However, the clinical effectiveness of these routes has not been compared. The aim of this study was to compare duration and efficacy of analgesia in children following adenotonsillectomy after acetaminophen either 40 mg kg(-1) rectally or 15 mg kg(-1) i.v.

Methods: Fifty children aged between 2 and 5 yr were recruited. They received a standardized anaesthetic, including 2 microg kg(-1) of fentanyl. Children were randomized to receive either rectal or i.v. acetaminophen. Postoperative pain was assessed regularly with the Children and Infants Postoperative Pain Scale score and rescue analgesia provided if scores were 4 or greater. The primary outcome measure was time to first analgesia. Results were plotted with a Kaplan-Meier analysis and median time to rescue analgesia compared between the groups.

Results: The protocol was successfully completed in 46 children. Forty-five children required rescue medication. The time to first rescue analgesia was longer in children receiving rectal acetaminophen (median 10 h, inter-quartile range 9-11 h) compared with those receiving i.v. acetaminophen (7, 6-10 h) with a P-value of 0.01 by log-rank test for equality in survivor function. Few children in either group required rescue analgesia within the first 6 h with differences between the groups being most prominent in the period from 6 to 10 h.

Conclusions: Rectal acetaminophen 40 mg kg(-1) provides longer analgesia for moderately painful procedures when compared with 15 mg kg(-1) acetaminophen i.v.