Alergia Elemental Libro

Alpha Blockers:
Selective alpha-adrenergic receptor blockers, such as prazosin and terazosin, block postsynaptic alpha-receptors, resulting- in both arterial and venous vasodilatation. Side effects include frequent orthostatic hypotension, especially with the first dose; dizziness; and headache.
Mixed Alpha-and Beta-Antagonists:
Mixed Alpha-and Beta-Antagonists, such as labetalol-andcarvedilol, antagonize both alpha and beta-adrenorecetors

Other Sympatholytics:
Older agents, such as reserpine and guanethidine, are rarely used because of significant side effects, such as depression, dizziness, postural hypotension, and diarrhea. These agents act by inhibiting the release of norepinephrine from peripheral neurons.

CENTRALLY ACTING AGENTS:
Centrally acting agents stimulatepresynaptic receptors in the CNS, causing peripheral vasodilatation via a decrease in sympathetic tone and systemic vascular resistance.
Clonídine ís available in both oral form and as a transdermal patch. Methyldope is safe to administer in pregnant patients. Side effects of these drugs may include drowsiness, dry mouth, sexually dysfunction and a lupus like syndrome with methyldopa.

Abruptcessation of these agents may result in an acute withdrawal syndrome manifested by tachycardia, diaphoresis, and accelerated HTN.

CALCIUM CHANNEL BLOCKERS:
Calcium channel blockers (CCBs) are effective in the treatment of HTN and act by selective blockade of the inwardly directed calcium channels in the smooth muscle cells of the vascular endothelium. Dihydropyridine CCBs include nifedipine as wellas the second generation drugs amlodipine, felodipine, isradipine, and nicardipine, which have longer half lives and are more vasoselective. These agents cause peripheral vasodilatation and may result in a mild reflex tachycardia. Nondihydropyridine CCBs include verapamil and these agents are associated with negative cardiac inotropìc and chronotropic effects.

INHIBITORS OF THE RENIN-ANGIOTENSIN SYSTEM

ACE Inhibitors:
ACE Inhibitors competitively inhibit the ACE responsible for the conversion of angiotensin I to its active vasoconstrictor form, angiotensin II. This results in arterial and venous dilation, plus mild natriuresis from the indirect lowering of plasma aldosterone. Major side effects include cough (believed to be secondary to increased bradykinins), angioneurotic edema,hyperkalemia, and a decrement in glomerular filtration rate, These agents are beneficial in patients with proteinuria or coexisting heart failure.

Angiotensin Receptor Blockers:
Angiotensin receptor blockers (ARBs) block the angiotensin-receptor: This is the receptor through which angiotensin II mediates its vaso-constrictive effects on smooth muscle and secretory effects on the zonaglomerulosa.

Thus, the action profile is similar to ACE inhibitors as are the side effects. However; as
ARBs do not interfere with bradykinin breakdown, they do not cause cough.
Angioedema is also distinctly less common with the use of ARBs. It is important to note that ARBs do not eliminate the potentially useful effects of angiotensin-II receptor blockade, as ARBs are specific for angiotensin-Ireceptors. ARBs may also protect against ACE inhibitor escape, which 'results from the non ACE conversion of angiotensin I to angiotensin II chymases in patients chronically treated with ACE inhibitors.

DIRECT VASODILATORS

Direct vasodilators, such as minoxidil and hydralazine, produce arterial vasodilation. Side effects include headache, nausea, postural hypotension, and drug-induced lupuswith hydralazine. Minoxidil may result in hypertrichosis and pericardial effusion

Choice of initial Antihypertensive Agent

Before 1995, The majority of data for improving outcomes with antihypertensive therapy were for thiazide diuretics and beta blockers. These data were reviewed in a metaanalysis by Psaty et al.: Beta blockers and high-dose diuretics were shown to decrease stroke and...