Two weeks after starting dapsone monotherapy, a young man develops rapid-onset pallor, fatigue, and dark urine. Peripheral smear shows Heinz bodies and bite cells. Screening for which enzyme deficiency should be done before continuing therapy?

• A Glucose-6-phosphate dehydrogenase ✓
• B Pyruvate kinase
• C NADH methaemoglobin reductase
• D Glutathione synthetase

Explanation

Dapsone is an oxidant drug that produces haemolysis and methaemoglobinaemia through its hydroxylamine metabolite. In G6PD deficiency, red cells cannot regenerate reduced glutathione to counter oxidative stress, leading to intravascular haemolysis with Heinz bodies and bite cells. G6PD levels should be checked before starting dapsone in susceptible populations. Methaemoglobin reductase deficiency causes cyanosis but not the acute haemolytic picture described here.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.