A 26-year-old woman with genetically confirmed acute intermittent porphyria is hospitalised during a severe attack with vomiting, abdominal pain, and progressive proximal weakness. Alongside withdrawal of the offending drug, which intervention directly targets the biochemical defect by repressing hepatic ALA synthase?

• A Regular therapeutic phlebotomy
• B Oral beta-carotene supplementation
• C Intravenous haem arginate (haemin) infusion ✓
• D Oral N-acetylcysteine

Explanation

Exogenous heme supplied as IV haem arginate or lyophilised haemin bypasses the blocked pathway and exerts feedback repression on hepatic ALAS1, lowering ALA and PBG levels and aborting the attack. High carbohydrate infusion is given as adjunct because calories also suppress ALAS1. Beta-carotene treats erythropoietic protoporphyria, phlebotomy treats porphyria cutanea tarda, and neither addresses the neurovisceral crisis. Weakness can progress to respiratory paralysis, so monitoring is essential.

Reference: Harrisons Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.