PLASMA-CONCENTRATIONS AFTER HIGH-DOSE (45MG-CENTER-DOT-KG(-1)) RECTALACETAMINOPHEN IN CHILDREN

Although the recommended dose of rectal acetaminophen (25-30 mg . kg(- 1)) is twice that for oral administration (10-15 mg . kg(-1) the liter ature justifies the use of a higher dose when acetaminophen is adminis tered via the rectal route. We measured venous plasma acetaminophen co ncentrations resulting from 45 mg . kg(-1) of rectal acetaminophen in ten ASA 1, 15 kg paediatric patients undergoing minor surgery with a s tandardized anaesthetic. After induction of anaesthesia, a single 650 mg suppository (Abeno(R), SmithKline Beecham Pharma Inc.) was administ ered rectally. Plasma was sampled at t = 0, 15, 30, 45, 60, 90, 120 18 0, 240 min in the first five patients and at t = 0, 30, 60, 90, 120, 1 80, 240, 300, 420 min in the subsequent five. Acetaminophen plasma con centrations were determined using a TDxFLx(R) fluorescence polarizatio n immunoassay (Abbott Laboratories, Toronto, Ontario). The maximum pla sma concentration war; 88 +/- 39 mu mol . L(-1) (13 +/- 6 mu g . ml(-1 )) and the time of peak plasma concentration was 198 +/- 70 min (mean +/- SD). At 420 min, the mean plasma concentration was 46 +/- 18 mu mo l . L(-1) (7.0 +/- 0.9 mu g . ml(-1)). No plasma concentrations associ ated with toxicity (>800 mu mol . L(-1)) were identified. A 45 mg . kg (-1) rectal dose of acetaminophen resulted in peak plasma concentratio ns comparable with those resulting from 10-15 mg . kg(-1) of oral acet aminophen at three hours after suppository insertion. It is concluded that the delayed and erratic absorption of acetaminophen after rectal administration leads to unpredictable plasma concentrations. Rectal ac etaminophen will not be consistently effective for providing rapid ons et of analgesia in children.