Effectiveness of delayed activated charcoal administration in simulated paracetamol (acetaminophen) overdose

Aims Oral activated charcoal is used to treat drug overdose and is effectiv e at reducing drug absorption when administered within 1 h of drug ingestio n. There are fewer data on efficacy when the delay is longer, as is the cas e in most drug overdoses. This study investigated the efficacy of activated charcoal at preventing paracetamol (acetaminophen) absorption after simula ted overdose when administration was delayed between 1 and 4 h. Methods An open randomized-order four-way crossover study was performed in healthy volunteers comparing the effect of activated charcoal 50 g on the a bsorption of 3 g paracetamol tablets when administered after an interval of 1, 2 or 4 h or not at all. Plasma paracetamol concentrations were measured over 9 h after paracetamol ingestion using h.p.l.c. and areas under the cu rve between 4 and 9 h (AUC(4,9 h)) calculated as a measure of paracetamol a bsorption. Results Activated charcoal significantly reduced paracetamol AUC(4,9 h) whe n administered after 1 h (mean reduction 56%; 95% Confidence intervals 34, 78; P < 0.002) or 2 h (22%; 6, 39; P < 0.03) but not after 4 h (8%; -8, 24) . When administered after 1 h activated charcoal reduced individual plasma paracetamol concentrations significantly at all times between 4 and 9 h aft er paracetamol administration. Administration at 2 or 4 h had no significan t effect. Conclusions These results in healthy volunteers cannot be extrapolated dire ctly to poisoned patients. However, they provide no evidence of efficacy fo r activated charcoal when administered after an interval of more than 2 h.