Evaluation and treatment of acetaminophen toxicity

A review of the typical clinical course, diagnosis and treatment of acetaminophen toxicity is provided. For an acute overdose, most adults must ingest about 12g or more acetaminophen (APAP) before risk of serious hepatotoxicity is of concern. A nomogram of serum APAP concentration vs hours post-ingestion can assist in determining risk of liver injury and need for treatment. However, histories concerning the time of ingestion and the amount of drug ingested are usually unreliable. Peak serum transaminase activities usually occur 48-96h after acute ingestion. It is possible for patients to present in liver failure days after ingestion with undetectable serum APAP concentrations. Patients who have chronically ingested excessive APAP doses and develop hepatotoxicity usually present with such, and renal failure is more common in this population. Current treatment centers on administration of N-acetylcysteine (NAC) to prevent hepatotoxicity, though NAC also improves outcomes in patients who present with acute liver failure. When given early after APAP ingestion, NAC's main mechanism of action is to maintain intracellular glutathione stores so to detoxify the electrophilic APAP metabolite, NAPQI. NAC is generally well-tolerated when given intravenously, with the main concern being anaphylactoid reactions. These reactions usually occur during loading doses and are easily treated with discontinuation of the NAC infusion, administration of antihistamines, and then restarting the loading dose at a slower infusion rate. There is concern that current NAC dosing is not large enough to adequately treat large APAP ingestions. Patients with acute liver failure may be candidates for orthotopic liver transplantation.