Porphyria Drug Contraindications — MFDS Part 1 MCQ
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Correct answer: D — Phenobarbital
Phenobarbital is the contraindicated drug. It is a barbiturate and a potent inducer of hepatic drug-metabolising enzymes; such induction can increase hepatic haem demand and precipitate an acute neurovisceral attack in susceptible patients. Its UK SmPC specifically lists acute intermittent porphyria as a contraindication. The distinction from non-acute porphyrias is important because the same general drug restrictions do not apply to every condition described as porphyria. Paracetamol and ibuprofen are considered safe analgesics in acute porphyrias. Amoxicillin is a safe antibacterial option, and lidocaine is considered safe when used as a dental local anaesthetic. Individual medicines should nevertheless be checked against current UK Porphyria Medicines Information Service advice when uncertainty remains.
Reference: Electronic Medicines Compendium. Phenobarbital Sodium 200 mg/ml Injection, Summary of Product Characteristics, section 4.3 Contraindications. Updated 1 April 2025. https://www.medicines.org.uk/emc/product/3607/smpc