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Morphine histamine release — FRCA Primary MCQ

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ModeratePharmacologyMorphine histamine releaseFRCA Primary

A 56-year-old man with asthma receives morphine for postoperative pain and develops pruritus, flushing and mild wheeze. Blood pressure is stable and there is no rash progression. Which of the following is correct regarding this reaction?

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Correct answer: C — It is caused by IgE-mediated mast-cell degranulation in most cases

Morphine can cause direct non-IgE histamine release, producing flushing, pruritus and bronchospasm, particularly in susceptible patients. True IgE-mediated allergy is much less common and would be suggested by more severe multisystem features. Fentanyl causes less histamine release and does not necessarily cross-react in this way. The pearl is to distinguish pharmacological histamine release from anaphylaxis while treating severe reactions promptly.

Reference: RCoA Primary FRCA Syllabus 2026; Peck, Hill & Williams Pharmacology for Anaesthesia