Effect of delayed activated charcoal on acetaminophen concentration after simulated overdose of oxycodone and acetaminophen

Objective. To determine the effect of activated charcoal (AC) on acetaminophen (APAP) absorption kinetics when administered at 1, 2, or 3 h after combined oral overdose with oxycodone. Methods. IRB-approved, prospective cross-over study of nine healthy human volunteers ingesting 5 g of APAP + 0.5 mg/kg of oxycodone on each of four study days. On the control day, subjects received no AC. On the remaining study days, subjects ingested 50 g of AC at 1, 2, or 3 h after drug ingestion. We measured serum APAP concentration hourly from 0 through 8 h and compared basic non-compartmental pharmacokinetic parameters. Results. Compared to the control, AC reduced area under the curve by 43% when given at 1 h (p 0.0001), 22% when given at 2 h (p = 0.02), and 15% when given at 3 h (p = 0.26). AC at 1 h resulted in a 25% reduction in peak APAP concentration from 48.6 to 36.3 mcg/mL (p = 0.012) with no significant difference when given at 2 or 3 h. There was no significant difference in elimination half-life among the four study days. Conclusion. The effect of AC rapidly declines between 1 and 3 h after combined oral overdose of APAP and oxycodone. AC is unlikely to be beneficial at or beyond 2 h after an overdose of acetaminophen and oxycodone.