Acetaminophen (N-Acetyl-p-Aminophenol; APAP)


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Subject: Acetaminophen (N-Acetyl-p-Aminophenol; APAP)

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  • Nonopioid analgesic, antipyretic


  • Relief of pain, such as headaches and toothaches

  • Reduction of fever


  • Screen of urine: indication of exposure

  • Screen of serum: used to assess potential toxicity

  • Normal range: 5–20 μg/mL serum

  • Potentially toxic: >150 μg/mL measured 4 hours postdose


  • Screening

    • Serum/urine: colorimetric or immunoassay on automated chemistry analyzers

      • High bilirubin concentrations [>50 μg/mL] may cause false-positive results with immunoassay-based tests.

      • Plasma may be tested in place of serum. Anticoagulants such as EDTA and heparin do not generally interfere with the assay.

      • Do not use whole blood.

  • Confirmation:

    • Serum/urine–HPLC or GC/MC

    • APAP is highly conjugated by glucuronidation and sulfation.

    • An assay that includes a hydrolysis step provides total APAP levels, which are not useful for assessing toxicity.