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Chokri Ben Lamine: Methemoglobinemia in Hematology – Causes, Diagnosis, Antidote
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Apr 30, 2026, 12:45

Chokri Ben Lamine: Methemoglobinemia in Hematology – Causes, Diagnosis, Antidote

Chokri Ben Lamine, Assistant consultant at King Faisal Specialist Hospital and Research Center, shared a post on X:

“Methemoglobinemia in Hematology – Causes, Dx, Antidote

What is it?

Hb Fe²⁺ to Fe³⁺ leading to cannot carry O₂

Resulting in functional anemia and tissue hypoxia

Common causes in Hematology

  • Dapsone (very common in PCP prophylaxis)
  • Trimethoprim-sulfamethoxazole (rare)
  •  Benzocaine / lidocaine
  • Nitric oxide
  • Rasburicase  (esp. G6PD)
  • Primaquine
  • Nitrates / nitrites

High risk:

  • G6PD deficiency
  • Renal failure
  • High-dose or prolonged exposure

Clinical clues

  • Dyspnea, fatigue
  • Cyanosis not improving with O₂
  • Headache, confusion
  • Severe: arrhythmia, coma

Diagnosis

  • ABG: normal PaO₂
  • Pulse ox approximately 85% (fixed, not improving)
  • Co-oximetry elevated reveals metHb % (confirm)

‘Saturation gap’ is key clue

Severity guide

  • less than 10% – often asymptomatic
  • 10–20% – cyanosis
  • 20–50% – symptoms (dyspnea, fatigue)
  • more than 50% – life-threatening

Treatment

1. STOP offending drug (e.g., Dapsone)

2.Methylene blue

  • Dose: 1–2 mg/kg IV over 5 min
  • Repeat in 1 hr if needed

Requires NADPH 

  • Avoid in G6PD deficiency (risk hemolysis)

If G6PD deficiency / refractory

  • Vitamin C (ascorbic acid) high dose
  • Exchange transfusion (severe)
  • Hyperbaric O₂ (rare cases)

Monitoring

  • Serial metHb levels
  • Clinical response (O₂ sat improves)
  • Watch for rebound (esp. dapsone long half-life)

Hematology pearl

  • Dapsone – delayed and recurrent methemoglobinemia
  • May need repeated treatment

Take-home

  • Cyanosis and normal PaO₂ – think metHb
  • Dapsone is the primary culprit in hematology patients
  • Treat fast with methylene blue (unless G6PD).”

Other posts featuring Chokri Ben Lamine on Hemostasis Today.

bleeding disorders Chokri Ben Lamine Dapsone Health Hematology Hemostasis Hemostasis News Hemostasis Today Medicine Methemoglobinemia Toxicology
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