A Case Report of a Severe, Unusually Delayed Anaphylactoid Reaction to Intravenous N-Acetylcysteine During Treatment of Acute Acetaminophen Toxicity in an Adolescent.

Abstract

Anaphylactoid reactions are well-documented adverse events associated with the intravenous administration of N-acetylcysteine (NAC) in patients with acetaminophen overdose. Most reactions are mild, occurring within the first 1-5hours of initiation. This report presents the case of an adolescent with a delayed, life-threatening anaphylactoid reaction 24.5hours after starting NAC, where discontinuing NAC could have resulted in fulminant hepatic failure (FHF) and death. A 17-year-old previously healthy female presented with nausea, vomiting, and abdominal pain 10hours after an acute acetaminophen ingestion. Her 11-hour serum acetaminophen concentration was above the treatment line (149μg/mL), and she had elevated transaminases (AST = 202U/L, ALT = 284U/L). She was treated with intravenous NAC, which was suspended for 3hours after she developed an apparent life-threatening anaphylactoid reaction with angioedema and respiratory distress 24.5hours after treatment initiation. Given her high risk of progression to FHF, NAC was resumed at double the previous rate along with scheduled corticosteroids and antihistamines after resolution of her symptoms. Her AST increased to 10,927U/L, and INR peaked at 3.6, but she had no further anaphylactoid symptoms. She was discharged in her normal state of health after 6days. Discontinuing NAC in this case of severe, delayed anaphylactoid reactioncould haveresulted in FHF requiring liver transplant. The reason for herreaction is unclear but could be related to patient risk factors or medication error. Guidelines for reinitiation of NAC after development of delayed anaphylactoid reactions are not well-established. Close observation beyond the first 1-5hours of NAC administration is warranted.