title: Lower incidence of anaphylactoid reactions to N-acetylcysteine in patients with high acetaminophen concentrations after overdose.
abstract: BACKGROUND
  Mechanisms responsible for anaphylactoid reactions to N-acetylcysteine (NAC) are poorly understood, and acetaminophen itself may play an important role. The present study examined the relationship between serum acetaminophen concentrations and risk of anaphylactoid reactions.
  
  
  METHODS
  Prospective study of adverse reactions to NAC administered according to standardized clinical protocols in patients who present to hospital after acute acetaminophen overdose. Subgroups were defined by serum acetaminophen concentrations 0 to 100 mg/L, 101 to 150 mg/L, 151 to 200 mg/L, 201 to 300 mg/L, and >300 mg/L.
  
  
  RESULTS
  There were 362 patients, and anaphylactoid reactions occurred in 14.9%. Anaphylactoid reactions occurred less commonly in patients with high serum acetaminophen concentrations (p = 0.046 by Cochran-Armitage trend test) and high equivalent 4 h acetaminophen concentrations (p = 0.004).
  
  
  CONCLUSIONS
  High serum acetaminophen concentrations were associated with fewer anaphylactoid reactions, suggesting that these might in some way be protective. The biological basis needs further exploration so as to allow a better understanding of the mechanisms responsible for adverse reactions to NAC treatment.
authors.affiliation: Scottish Poisons Information Bureau, The Royal Infirmary of Edinburgh, Edinburgh, United Kingdom. s.waring@ed.ac.uk
authors.forename: W Stephen
authors.initials: WS
authors.lastname: Waring
authors.forename: Alexandra F
authors.initials: AF
authors.lastname: Stephen
authors.forename: Oliver D
authors.initials: OD
authors.lastname: Robinson
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Dow
authors.forename: Janice M
authors.initials: JM
authors.lastname: Pettie
mesh_terms: D000082:Acetaminophen / Q000493:pharmacokinetics* / Q000506:poisoning; D000111:Acetylcysteine / Q000009:adverse effects* / Q000627:therapeutic use; D000328:Adult; D018712:Analgesics, Non-Narcotic / Q000493:pharmacokinetics* / Q000506:poisoning; D000707:Anaphylaxis / Q000139:chemically induced* / Q000453:epidemiology; D000931:Antidotes / Q000009:adverse effects* / Q000627:therapeutic use; D004347:Drug Interactions; D062787:Drug Overdose; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies
chemical_list: D018712:Analgesics, Non-Narcotic; D000931:Antidotes; D000082:Acetaminophen; D000111:Acetylcysteine