Alpha-blocker prazosin

CENTRALLY ACTING ANTI HYPERTENSIVES -CLONIDINE ALPHA-BLOCKERS-PRAZOSIN Small case series indicate that prazosin may 1 the antihypertensive effect of donidine Uncertain at present Monitor BP at least weekly until stable... 

Agonist 1 increases HR, presumably through direct activation of cardiac P receptors because the effect is blocked by propranolol but is not influenced by the alpha blocker (prazosin), the ganglion blocker (trimethaphan), or blockade of M receptors (atropine). Only two of the listed drugs directly activate cardiac receptors epinephrine and norepinephrine. For NE, any direct cardiac stimulation is counteracted by reflex bradycardia resulting from the increase in mean BP via its activation of a, receptors in blood vessels (it has no effects... 

Selective alpha-blockers Prazosin and other a, blockers are used in hypertension (see Chapter 11). Selective a,-blockers have also found increasing use in the management of urinary hesitancy and prevention of urinary retention in men with prostatic hyperplasia. 

The alpha blocker prazosin (Minipress) to the client with a serum sodium level of 137 mEq/L. 

Geriatric Considerations - Summary Alpha-adrenergic blockers are modestly effective alone, and in combination with 5-alpha reductase inhibitors (e,g, finasteride) in the treatment of urinary obstructive symptoms related to benign prostatic hyperplasia. Alfuzosin is a "uroselective" alpha-blockerwhich appears to cause less orthostatic hypotension than nonselective alpha-blockers such as terazosin, prazosin, and doxazosin. 

Sotalol (Betapace) Timolol (Blocadren) Alpha blockers Doxazosin (Cardura) Phenoxybenzamine (Dibenzyline) Prazosin (Minipress) Terazosin (Hytrin) Trimethaphan (Arfonad)... 

The characteristics of individual alpha blockers are discussed in Chapter 20. Basically, these drugs can be differentiated according to their relative alpha-1 selectivity, their duration of action, and other pharmacokinetic properties. Prazosin (Minipress) has been the primary alpha blocker used in the past, but newer agents such as doxazosin and terazosin (Hytrin) are gaining acceptance in treating hypertension. Prazosin and other alpha blockers approved as antihypertensives are listed in Table 21-4. 

ALPHA-BLOCKERS BETA-BLOCKERS t efficacy of alpha-blockers t risk of first-dose 1 BP when alfuzosin, prazosin or terazosin is started in patients already taking beta-blockers Additive hypotensive effect may be used therapeutically Monitor BP at least weekly until stable. Warn patients to report symptoms of hypotension (lightheadedness, dizziness on standing, etc.). Watch for first-dose 1 BP... 

ALPHA-BLOCKERS CARDIAC GLYCOSIDES Possibility of T plasma concentrations of digoxin no cases of toxicity have been reported with doxazosin or prazosin Doxazosin inhibits P-gp-mediated elimination of digoxin mechanism with prazosin is uncertain at present Monitor digoxin levels... 

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. 

There is some evidence that male sexual dysfunction occurs less often with alpha-blockers than with other types of anti-hjrpertensive drugs (2). For example, in a comparison of the effects of prazosin and hydrochlorothiazide on sexual function in 12 hjrpertensive men, plethysmographic measurements and subjective assessments showed less dysfunction with prazosin than with hydrochlorothiazide (3). There is no evidence that this effect can be used therapeutically, but cases of priapism have been reported for example, a 55-year-old man presented with priapism having taken prazosin 7.5 mg tds for 4 months. After a further 3 months, prazosin was discontinued and erectile function became normal (4). 

Certain beta-blockers such as propranolol, metoprolol, and pindolol, and alpha-blockers such as prazosin, may cause impotence or a decrease in libido, which is usually dose related and should be... 

Clinically important, potentially hazardous interactions with albuterol, alpha-blockers, amitriptyline, amoxapine, atenolol, beta-blockers, carteolol, chlorpromazine, clomipramine, cocaine, desipramine, doxepin, ephedra, ergotamine, furazolidone, halothane, imipramine, insulin detemir, MAO inhibitors, metoprolol, nadolol, nortriptyline, oxprenolol, penbutolol, phenelzine, phenoxybenzamine, phenylephrine, pindolol, prazosin, propranolol, protriptyline, sympathomimetics, terbutaline, thioridazine, timolol, tranylcypromine, tricyclic antidepressants, trimipramine, vasopressors... 

Of the drugs listed, only isoproterenol causes a decrease in mean blood pressure, because it activates beta receptors and has no effect on alpha receptors. This permits identification of drug 3 as isoproterenol. Prazosin is an alpha blocker, so one can anticipate that this drug would antagonize any increases in blood pressure that result from activation of (Xj receptors in the vasculature. Epinephrine (high dose), norepinephrine, and tyramine all exert pressor effects via activation of (Xj receptors. However, only epinephrine is active on P2 receptors, and this action would be revealed by vasodilation and a reversal of its pressor effects following treatment with an alpha blocker— epinephrine reversal. Thus, drug 4 can be identified as epinephrine. 

The newer selective alphaj-adrenoreceptor-blocking agents, such as trimazosin, doxasozin, and terazosin, display a pharmacologic profile virtually identical to that of prazosin, but pharmacokinetic differences between the various alpha,-blockers exist. 

The nonselective alpha blockers (phentolamine, phenoxybenzamine) are described. The a,-selective blockers (e.g., prazosin) are used in hypertension and BPH. 

Selective alpha-blockers Because prazosin and its analogs block vascular a, receptors much more effectively than the a,-modulatory receptors associated with cardiac sympathetic nerve endings, these drugs cause much less tachycardia than the nonselective alpha-blockers when reducing 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. 

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