Background: The purpose of this study was to measure the plasma levels and analgesic effectiveness of a dose of 40 mg x kg(-1) of preoperative oral acetaminophen.
Methods: Thirty children aged 55 (17-72) months undergoing bilateral myringotomy and tube insertion (BMT) received acetaminophen 40 mg x kg(-1) p.o. preoperatively. Plasma levels were measured, at 29 (10-51) min and at 60 min in the postanaesthesia care unit (PACU). Children's Hospital of Eastern Ontario Pain Scale (CHEOPS), for all subjects and the Poker Chip Tool (PCT) a self-report scale for subjects aged > 4 years, were used. After discharge, 24-h analgesic efficacy was evaluated using an observer Visual Analogue Scale (VAS) score and further acetaminophen use was recorded.
Results: Plasma concentrations were 259 (60-391) micromol x l(-1) and 250 (135-450) micromol x l(-1), respectively. All 60 min plasma concentrations were > or = 70 micromol x l(-1) (ED50 for adenotonsillectomy) and less than 800 micromol x l(-1) (associated with toxicity). Twenty-six subjects (87%) had adequate analgesia (CHEOPS < or = 8). The PCT was only understood in the PACU by 13 of the 21 children > 4 years (62%). The median worst 24-h observer VAS was 0.5 (0-5.5) (27 subjects). No further analgesic was required after discharge in 16/28 (57%). A higher plasma level was associated with fewer doses of acetaminophen after discharge (r = -0.36, P=0.05).
Conclusions: No relationship was evident between age, the 60 min plasma acetaminophen level and the CHEOPS carried out at the same time. Acetaminophen 40 mg x g(-1) p.o. results in 60 min plasma levels of 250 (135-450) micromol x l(-1). The in-hospital analgesic efficacy was 87% (CHEOPS < 9, no further analgesics) and the 24-h efficacy was 57% (need for further acetaminophen).