MCQ on antianginal agents: Page-3

One of the important limitation of the nitrovasodilators is their tolerance. Organic nitrates when used for long period develop tolerance towards their vasodilatory effects. Neither metabolism nor clearance is responsible for tolerance. Organic nitrates not act on any receptor but act by release of nitric oxide which increases cGMP. The tolerance is may be due to decreased release of nitric oxide from organic nitrates due to depletion of thiol groups in the tissues or due to any alteration in cGMP activity. The tolerance can be prevented by nitrate-free intervals. Hence long acting organic nitrates should be give 12-hour nitrate free interval to restore their activity.

Amlodipine is long acting vasodilator used in treatment of hypertension. Nimodipine is selective for cerebral blood vessels and indicated for cerebral vasospasm.

Calcium channel blockers can act on L-type calcium channels which are present on heart and smooth muscle. Verapamil acts on heart and nifedipine acts on smooth muscle. So they decrease heart rate and produce vasodilation respectively. At the same time, as they block calcium channels, decrease the contractility of the heart which is more pronounced with verapamil. Hence CCBs are contraindicated in heart failure.

Natriuretic peptides are released in heart failure as a compensatory mechanism and cause dilatation of afferent arterioles leading to increased excretion of sodium and water.

Ivabradine is a new drug that blocks sodium-potassium channels in pacemaker potential thereby decreases automaticity. Hence it can be used instead of betablockers.