Use of activated charcoal in a simulated poisoning with acetaminophen: a new loading dose for N-acetylcysteine?

To investigate the ability of a supranormal dose of N-acetylcysteine to overcome the effects of activated charcoal on N-acetylcysteine bioavailability and to determine the effects of activated charcoal on serum acetaminophen levels.

Ten healthy adult volunteers participated in a controlled cross-over experiment. During phase I (control), subjects ingested 3 g acetaminophen, followed one hour later by the normal loading dose of N-acetylcysteine (140 mg/kg). During phase II (charcoal), subjects ingested 3 g acetaminophen, followed one hour later by 60 g activated charcoal and a supranormal loading dose of N-acetylcysteine (235 mg/kg).

Serum levels of N-acetylcysteine were measured every 30 minutes for six hours. A serum acetaminophen level was measured at four hours.

The area under the curve for N-acetylcysteine was significantly higher for phase II than phase I (P < .05, two-tailed paired t-test). Peak N-acetylcysteine and time to peak were not significantly different. The four-hour serum acetaminophen level was significantly lower for phase II than phase I (P < .05, two-tailed paired t-test). Diarrhea occurred during both phases, but N-acetylcysteine was otherwise well tolerated.

These results suggest that activated charcoal can be used safely for victims of acetaminophen overdose. A beneficial effect in preventing acetaminophen absorption can be expected if it is given within one hour after ingestion. If N-acetylcysteine is needed because of a toxic serum acetaminophen level, bioavailability can be ensured by increasing the N-acetylcysteine loading dose from 140 mg/kg to 235 mg/kg.