Ipratropium Bronchodilation — FRCA Primary MCQ
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Correct answer: C — Blockade of bronchial muscarinic receptors, reducing IP3-mediated calcium mobilisation
Explanation lettering: E = shown as C · C = shown as D · D = shown as E
E is correct. Ipratropium is a quaternary ammonium antimuscarinic drug. It antagonises acetylcholine at muscarinic receptors on bronchial smooth muscle, thereby inhibiting vagally mediated bronchoconstriction. Muscarinic receptor activation normally stimulates the Gq–phospholipase C–IP3/DAG pathway, increasing intracellular calcium and smooth-muscle contraction. Receptor blockade reduces calcium mobilisation and causes bronchodilation, predominantly through a local airway effect. Beta-2 agonists produce bronchodilation by increasing cyclic AMP (A). Leukotriene receptor antagonists such as montelukast act by mechanism B. Phosphodiesterase inhibitors increase cyclic AMP by reducing its degradation (C), while cromoglicate stabilises mast cells (D).
Reference: Cipla EU Ltd. Ipravent CFC-Free Inhaler 20 micrograms per actuation: Summary of Product Characteristics, section 5.1 Pharmacodynamic properties. Revised 2024. https://www.medicines.org.uk/emc/product/10148/smpc