Advantages and disadvantages of alpha 2-adrenoceptor agonists for systemic hypertension.

Alpha 2-receptor agonists are effective antihypertensive drugs that reduce sympathetic activity by both central and peripheral mechanisms. Plasma noradrenaline and renin concentrations are reduced. Hemodynamic disturbances are minor with a near-normal cardiovascular response to standing, exercise and volume depletion. The main problems are due to central adverse effects, particularly sedation, and a syndrome of sympathetic overactivity on sudden withdrawal. These problems can be minimized by using lower doses, while therapy with a useful antihypertensive drug is maintained. Clonidine and its analogs have a low toxicity and very few contraindications. They remain a useful part of the therapeutic armamentarium in hypertension.