Acetaminophen is rapidly absorbed from the gastrointestinal tract, with peak levels occurring 1-3 hours after ingestion. Serum levels drawn less than 4 hours after ingestion may not represent peak levels. The normal half-life of the drug is approximately 3 hours. A half-life of greater than 4 hours indicates impaired metabolism and potential for hepatic injury. Toxicity due to acetaminophen should be monitored by determining both serum concentration and rate of clearance (half-life). An elevated serum acetaminophen with a half life of greater than 4 hours indicates a high likelihood of hepatic injury. The hepatic toxicity of acetaminophen is related to the formation of one or more highly reactive metabolites in the liver. Orally administered N-acetylcysteine (Mucomyst) has been shown to provide protection against acetaminophen toxicity. The patient's condition should be monitored clinically for hepatotoxicity. Liver function tests may be indicated.