Effect of N-acetylcysteine on the pharmacokinetics of acetaminophen in rats

Oral administration of N-acetylcysteine (163 mg/kg at zero time and 82 mg/kg 30 minutes later) to adult male Sprague-Dawley rats given an intravenous injection of acetaminophen, 150 mg/kg at zero time, increased the formation of acetaminophen sulfate and thereby enhanced the elimination of acetaminophen. Apparently, N-acetylcysteine is an in vivo source of inorganic sulfate since availability of the latter is rate-limiting in the formation of acetaminophen sulfate. Increased metabolic conversion of acetaminophen to its sulfate conjugate results in decreased formation of other metabolites of acetaminophen, presumably including the reactive metabolite responsible for the hepatotoxic effect of the drug. This may account, at least in part, for the protective effect of N-acetylcysteine against acetaminophen-induced hepatotoxicity.