Isoprenaline (isoproterenol) is used as a temporary bridge in complete heart block pending pacemaker insertion. Which of the following adverse effects is most likely with this drug in this setting?

• A Hypertension due to peripheral vasoconstriction
• B Bronchoconstriction due to beta-2 blockade
• C Bradycardia due to vagal reflex
• D Ventricular arrhythmias due to increased myocardial automaticity ✓

Explanation

Isoprenaline is a non-selective beta agonist (beta-1 + beta-2) with no alpha activity. Stimulation of beta-1 receptors increases heart rate, conduction velocity, and myocardial automaticity, predisposing to ventricular arrhythmias including ventricular tachycardia and fibrillation — the main limiting adverse effect. It causes peripheral vasodilation (not vasoconstriction) via beta-2 receptors and bronchodilation, not bronchoconstriction.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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