HPI

• 32  year old male p/w possible medication overdose
• Pt reports  3-4 days taking 6g of acetaminophen daily for dental pain
• Pt c/o some abdominal cramping with nausea/vomiting

PMHx

• hypertension

Physical Exam

T: 100.6  HR 80 BP 140/90 Pox 86% on RA and 86% on 4L nasal canula

• General: appears comfortable in no distress

Laboratories

• Lactate 2.2
• ALT 9332 AST 9330 Tbili 9.2
• PT 17.5 INR 1.5
• Hepatitis panel negative
•  COVID Ag/PCR neg
• ABG: pH 7.5 PCO2 24 PO2 186 HCO3 22.5
• Methemoglobin 9.1 (ref range 0.0-1.5%)
•  Ammonia 101
• Acetaminophen <5

 Case Discussion

• Our patient has a negative tylenol level, but elevated LFTs and last tylenol use was 24 hours ago
• Another indication for NAC is any evidence of liver injury (rise in ALT/AST)
• What about the elevated methemoglobin level?? 

 Proposed mechanisms for methemoglobinemia in acetaminophen overdose:

• NAPQI-induced oxidation
• Depletion of glutathione stores
• Production of oxidant-metabolites including paraaminophenol
• G6PD deficiency results in inability to reduce NADP to NADPH
  

Management

•  

  Patient was found to be G6PD deficient at 3 U/gHb (Ref 9.9-16.6)

• G6PD is necessary to reduce methemoglobin
• Giving methylene blue in this case would worsen the oxidative stress as it accumulates without G6PD
• NAC was started given liver injury
•  
  

  Patient was evaluated for transplant but liver enzymes began to downtrend and patient labs improved along with clinical status

• Patient ultimately discharged in good condition from the hospital

Key Points

• Acetaminophen is a rare cause of methemoglobinemia
• Remember methemoglobinemia as a potential complication of acetaminophen overdose in patients with G6PD deficiency

References

 Rianprakaisang T, Blumenberg A, Hendrickson RG. Acetaminophen-associated methemoglobinemia. Clin Toxicol (Phila). 2020;58(7):785-786. doi:10.1080/15563650.2019.1682153

Rumack BH, Matthew H. Acetaminophen poisoning and toxicity. Pediatrics. 1975;55(6):871-876.