Antihypertensive drugs sympatholytic

Antihypertensive drugs can be divided into eight classes based on the mechanism of action diuretics, )3-adrenoblockers, centrally acting sympatholytics, peripherally acting sympatholytics, calcium channel blockers, myotropic hypotensive drugs, angiotensin-con-verting enzyme inhibitors, and calcium channel activators. 

Hydralazine was one of the first orally active antihypertensive drugs marketed in the United States. Its structure is shown in Figure 12.4. Initially, the drug was used infrequently because of its propensity to produce reflex tachycardia and tachyphylaxis. However, with a better understanding of the compensatory cardiovascular responses that accompany use of arteriolar vasodilators (the drug has little or no effect on venous smooth muscle), hydralazine was combined with sympatholytic agents and diuretics with greater therapeutic success. 

IV. Diagnosis is based on the history of ingestion, accompanied by bradycardia and hypotension. Other drugs that may cause a similar presentation after overdose include sympatholytic and antihypertensive drugs, digitalis, and calcium channel blockers. 

C. Hypertensive crisis associated with sudden withdrawal of sympatholytic antihypertensive drugs (eg, clonidine). 

In addition to the diuretics, which are listed separately, first-line antihypertensive drugs may be grouped into three categories sympatholytic agents ([jS] and [a] blockers. 

To circumvent problems, encourage patient compliance, avoid excessive doses, avoid combining sympatholytics and -blockers, and maintain antihypertensive medication in surgical patients. When discontinuing medication, taper the dose slowly, one drug at a time use special caution in patients with coronary artery or cerebrovascular disease. 

C. Trimethaphan is a ganglionic blocking agent that will lower blood pressure very rapidly. Hydralazine is a vasodilator hydrochlorothiazide and spironolactone are diuretics and methyldopa is a sympatholytic acting in the central nervous system. All of these drugs are used clinically as antihypertensive agents. None work as rapidly as trimethaphan. Clinically, however, either nitroprusside or clonidine is used much more commonly than trimethaphan in this situation. 

As noted above, serotonin synthesis can be inhibited by p-chlorophenylalanine andp-chloroamphetamine. However, these agents are too toxic for general use. Storage of serotonin can be inhibited by the use of reserpine, but the sympatholytic effects of this drug (see Chapter 11 Antihypertensive Agents) and the high levels of circulating serotonin that result from release prevent its use in carcinoid. Therefore, receptor blockade is the major approach to therapeutic limitation of serotonin effects. 

THERAPEUTIC USES Minoxidil is reserved for the treatment of severe hypertension that responds poorly to other antihypertensive medications, especially in male patients with renal insufficiency. Minoxidil must be given concurrently with a diuretic to avoid fluid retention and with a sympatholytic drug (usually a fi receptor antagonist) to control reflex cardiovascular effects. The drug usually is administered either once or twice a day, but some patients may require more frequent dosing for adequate control of blood pressure. The initial daily dose of minoxidil may be as little as 1.25 mg, which can be increased gradually to 40 mg in one or two daily doses. 

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