Beta-blocking drugs selectivity

Beta-blockers. There is some evidence that beta-adrenergic blocking drugs such as propranolol can cause bronchoconstriction in some patients. Some selectivity with beta2-adrenergic drugs can minimise this effect but caution should be exercised. 

Answer B. Propranolol is a nonselective blocker of beta adrenoceptors, whereas meto-prolol is Pj -selective. Metoprolol is less likely to block receptors in the bronchiolar smooth muscle and is less likely to cause bronchoconstriction, especially in asthmatic patients. Propranolol and metoprolol are considered to be equally effective as antiarrhythmics and in post-MI prophylaxis, and both are cardiodepressant. Drugs that appear to have both alpha- and beta-blocking actions include carvedilol and labetalol. 

Drug Beta j-receptor selectivity Alpha-blocking activity ISA Lpophilicity Bioavailability First pass metabolism Metdbo/i m... 

Clinically useful beta antagonists are classified as beta-l-selective if they predominantly affect the beta-1 subtype they are classified as beta-nonselective if they have a fairly equal affinity for beta-1 and beta-2 receptors (see Table 20-2). Beta-l-selective drugs are also referred to as cardioselective because of their preferential effect on the myocardium. Even if a beta antagonist is nonselective (i.e., blocks both beta-1 and beta-2 receptors), the beta-1 blockade is clinically beneficial. When stimulated, beta-2 receptors, which... 

Labetalol [Normodyne, Trandate). Labetalol is a nonselective beta blocker. This drug appears to have some alpha-1-selective blocking effects. Labetalol is used primarily in the management of hypertension and, while usually given orally, may be injected intravenously in emergency hypertensive situations. 

Systemic absorption may occur when eye drops containing beta-blockers are administered. Beta-receptors are found in heart muscle (predominantly beta-1) and the smooth muscle of the blood vessels and bronchioles (mainly beta-2). Selective beta-blockers (atenolol, bisoprolol, metoprolol, nebivolol, acebutolol) primarily (but not exclusively) antagonize beta-1 receptors, while the non-selective drugs (carvedilol, celiprolol, esmolol, labetalol, nadolol, oxprenolol, pindolol, propanolol, sotalol, timolol) block both beta-1 and beta-2 receptors,... 

Receptor selectivity Beta, receptor selectivity (p, block > p block), is a property of acebu-tolol, atenolol, esmolol, metoprolol. and several other beta-blockers. This property may be an advantage when treating patients with asthma. Butoxamine, a P -selective drug, is used only in research. Nadolol, propranolol, and timolol are typical nonselective beta-blockers. 

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