Alpha-adrenoceptor blockers

A. Classification and Prototypes Ketanserin is a S-HT and alpha-adrenoceptor blocker. Phe-noxybenzamine (an alpha-adrenoceptor blocker) and cyproheptadine (an Hj blocker) are also good 5-HTj blockers. Ondansetron, granisetron, dolasetron, and alosetron are 5-HTj blockers. The ergot alkaloids are partial agonists at 5-HT and other receptors (see below). 

Alpha-1-proteinase inhibitor, 12 147 a-adrenoceptor blockers, antihypertensive agents, 5 155-156t, 157t, 160... 

Alpha-blocker a drug that blocks alpha adrenoceptors. 

Alpha-adrenoceptor antagonists. Prazosin, afluzosin, indoramin, terazosin and doxazosin are all a-adrenoceptor blockers, with selectivity for the a -subtype. They cause significant increases (compared to placebo) in objective measures such as maximal... 

Buflomedil hydrochloride is a vasoactive drug with a variety of actions. It is an alpha-adrenoceptor antagonist and a weak calcium channel blocker. It inhibits platelet aggregation and improves erythrocyte deformability. However, its mechanism of action in peripheral vascular disease is not known. 

Oral decongestants should also be avoided by patients taking beta-blockers, as sympathomimetics stimulate both the alpha-adrenoceptors of the cardiovascular system to produce vasoconstriction and the beta-adrenoceptors to produce vasodilatation and stimulation of the heart. The overall effect is a slight increase in both blood pressure and heart rate. If the beta-receptors are blocked, unopposed alpha-adrenoceptor-mediated vasoconstriction can lead to a rise in blood pressure. 

E. Adrenoceptor Blockers Alpha -selective agents (eg, prazosin) and beta-blockers (eg, propranolol) are effective antihypertensive drugs. Alpha-blockers reduce vascular resistance and venous return. The nonselective alpha-blockers (phentolamine, phenoxybenzamine) are of no value in chronic hypertension because of excessive compensatory responses, especially tachycardia. Alpha,-selective adrenoceptor blockers are relatively free of the severe adverse effects of the nonselective alpha-blockers and postganglionic nerve terminal sympathoplegic agents. 

The double whammy—additive detrimental effects and novel adverse reactions Combination therapy takes advantage of synergistic mechanisms of antihypertensive action, but this can also be detrimental, particularly if patients are over-treated, leading to dizziness and orthostatic hypotension. Additive effects of certain combinations can also exacerbate adverse reactions that are common with individual agents. For example, calcium channel blockers and alpha-adrenoceptor antagonists both cause peripheral edema, which can be severe if these agents are used together. 

Indoramin is a postsynaptic selective alphai-adrenoceptor antagonist that is chemically distinct from the quinazo-lines. Unlike some other alpha-blockers, indoramin lowers blood pressure without a resulting reflex tachycardia or postural hypotension (1). However, it has largely been supplanted by more modern drugs, such as doxazosin, prazosin, and terazosin. 

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. 

Both alpha- and beta-adrenoceptors are blocked by labetalol Glucagon can be useful in reversing cardiac depression caused by a beta blocker They mask the signs of developing hyperthyroidism Treatment of glaucoma commonly involves the topical use of propranolol... 

Urapidil is an alpha-blocker and has a central sympatholytic effect mediated by stimulation of central 5HTia receptors. The authors of a review have suggested that there is a lower incidence of tachycardia and orthostatic hypotension with urapidil than with other a-adrenoceptor antagonists and no apparent increased risk of heart failure [101 ]. 

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