By what mechanism does prilocaine produce methaemoglobinaemia?
- A The parent drug directly oxidises haemoglobin iron
- B Its metabolite o-toluidine oxidises the ferrous iron of haemoglobin to the ferric form ✓
- C It inhibits NADH-cytochrome b5 reductase irreversibly
- D It binds haemoglobin to form stable sulphaemoglobin
Correct answer: B. Its metabolite o-toluidine oxidises the ferrous iron of haemoglobin to the ferric form
Explanation
Prilocaine is metabolised to o-toluidine, which oxidises the ferrous iron of haemoglobin to ferric iron, creating methaemoglobin that cannot carry oxygen. The risk rises sharply above doses of about 600 mg, and treatment is methylene blue, which restores the reduced form through the NADH-methaemoglobin reductase pathway. The reductase enzyme is not inhibited by the drug, and sulphaemoglobin formation involves sulphur compounds, not prilocaine.
Reference: Katzung Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.