Bilirubin Elevation Caused by Naproxen Overdose: A Case Report Highlighting Laboratory Interference.

Area of Science:

• Clinical Toxicology
• Pharmacology
• Laboratory Medicine

Background:

• Over-the-counter (OTC) drug overdoses, including NSAIDs like naproxen, are rising in the US.
• NSAID toxicity presents with nonspecific symptoms such as nausea, vomiting, abdominal pain, and headaches, potentially progressing to confusion, seizures, and renal failure.

Observation:

• A 63-year-old male with a history of hyperthyroidism and polysubstance use presented with suicidal ideation and vague abdominal pain after ingesting 16 naproxen tablets.
• Initial medical workup revealed an elevated total bilirubin level, with no other significant findings or abnormalities in hemolysis, biliary stasis, or hepatic dysfunction.
• Indirect hyperbilirubinemia resolved spontaneously within 24 hours following supportive care with intravenous fluids and antiemetics.

Findings:

• The elevated total bilirubin was attributed to the naproxen metabolite O-desmethylnaproxen (ODMN).
• ODMN is known to interfere with specific bilirubin assays when naproxen is ingested at supratherapeutic doses.
• Other causes of hyperbilirubinemia were systematically ruled out, confirming the drug-related interference.

Implications:

• Supratherapeutic naproxen ingestion can cause laboratory abnormalities (elevated total bilirubin) due to assay interference by ODMN.
• Clinicians should consider potential laboratory error when interpreting bilirubin levels in patients with a history of significant OTC drug ingestion, especially when clinical findings are incongruent.
• This highlights the importance of considering drug interactions and metabolite effects in toxicology cases, particularly with the increasing trend of OTC drug misuse for self-harm.