Antihypertensive drugs adrenoceptor blockers

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. 

Prazosin and its derivatives that are selective for aj-adrenoceptors are quite useful for the management of primary hypertension. The aj-receptor-selective antagonists can be used alone in mild hypertension. When hypertension is moderate or severe, prazosin is generally administered in combination with a thiazide and a 13-blocker. The antihypertensive actions of prazosin are considerably potentiated by coadministration of thiazides or other types of antihypertensive drugs. 

Summation or addition occurs when the effects of two drugs having the same action are additive, i.e. 2 + 2 = 4 (a p-adrenoceptor blocker plus a thiazide diuretic have an additive antihypertensive effect). 

P-adrenoceptor blockers lose some antihypertensive efficacy when nonsteroidal anti-inflammatory drugs (NSAIDs), especially indomethacin, are coadministered the effect involves inhibition of production of vasodilator prostaglandins by the kidney leading to sodium retention. 

Prostaglandin synthesis. Nonsteroidal anti-inflammatory drugs (NSAIDs), e.g. indomethacin, attenuate the antihypertensive effect of p-adrenoceptor blockers and of diuretics, perhaps by inhibiting the synthesis of vasodilator renal prostaglandins. This effect can also be important when a diuretic is used for severe left ventricular failure. 

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