Activated charcoal and acetylcysteine absorption: issues in interpreting pharmacokinetic data.

Studies determining the effects of activated charcoal on drug absorption frequently use area under the plasma drug concentration versus time curve or drug and metabolite recovery in the urine as endpoints. The considerations in using these endpoints is presented using studies that have evaluated the effects of activated charcoal on acetylcysteine absorption. Acetylcysteine's pharmacokinetics, quantitation of plasma concentrations, and the lack of an identifiable pharmacokinetic-pharmacodynamic relationship all contribute to the difficulties in determining whether activated charcoal inhibits the oral absorption of acetylcysteine, or alters acetylcysteine's efficacy in treating acetaminophen overdoses. The results of these studies should be interpreted cautiously, with consideration of internal and external study validity.