Adrenoceptor blockers beta-blocking drugs

Beta-adrenoceptor blockers block the sympathetic system antagonising the effect on the lungs, resulting in bronchoconstriction. Non-steroidal anti-inflammatory drugs inhibit prostaglandin synthesis, which may lead to bronchoconstriction. 

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. 

Labetalol is administered as a combination of four stereoisomers (Table 1) [9-11]. Whereas the RR isomer is mostly responsible for the p blocking activity of the drug, the SR isomer is most potent as an a-adrenoceptor blocker [9]. Both the RS and SS isomers, on the other hand, display weak antagonistic activities against a and p receptors [9]. Stereoselectivity in antagonism of beta adrenoceptors has also been reported [11] for nadolol (Fig. 1), another beta-blocker with four stereoisomers (Table 1). 

Propranolol was the first B-blocker shown to be effective in hypertension and ischemic heart disease. It is now clear that all (3-adrenoceptor-blocking agents are very useful for lowering blood pressure in mild to moderate hypertension. In severe hypertension, D-blockers are especially useful in preventing the reflex tachycardia that often results from treatment with direct vasodilators. Beta blockers have been shown to reduce mortality in patients with heart failure, and they are particularly advantageous for treating hypertension in that population (see Chapter 13 Drugs Used in Heart... 

All of the p-adrenergic blockers possess at least one center of asymmetry that confers optical activity to the drug. Beta-adrenoceptor blocking agents are generally used for the treatment of cardiovascular diseases, such as... 

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