Alpha-1 Adrenergic Blockers

Mechanism of action

Act at post-synaptic alpha-1 receptors to produce arteriole and venous vasodilation
alfuzosin (Uroxatral ® ) doxazosin (Cardura ® )
prazosin (Minipress ® ) silodosin - RAPAFLO®
tamsulosin ( Flomax ® ) terazosin (Hytrin ® )
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alfuzosin  (Uroxatral ® ) top of page

Oral: Adults:
: 10 mg once daily

Dosage adjustment in renal impairment: Bioavailability and maximum serum concentrations are increased by ~50% with mild, moderate, or severe renal impairment

Note: Safety has not been evaluated in patients with creatinine clearances <30 mL/minute.

Dosage adjustment in hepatic impairment:
Mild hepatic impairment: Use has not been studied.
Moderate or severe hepatic impairment (Child-Pugh class B and C): Clearance is decreased 1 /3 to 1 /4 and serum concentration is increased three- to fourfold; use is contraindicated

Tablet should be swallowed whole; do not crush or chew. Administer once daily (with a meal); should be taken at the same time each day.

[ Supplied: 10mg extended release tablet.]

doxazosin  (Cardura ® ) top of page

Mechanism of Action
The mechanism of action of CARDURA (doxazosin mesylate) is selective blockade of the alpha1 (postjunctional) subtype of adrenergic receptors. Studies in normal human subjects have shown that doxazosin competitively antagonized the pressor effects of phenylephrine (an alpha1 agonist) and the systolic pressor effect of norepinephrine. Doxazosin and prazosin have similar abilities to antagonize phenylephrine.

Oral:  Adults: 1 mg once daily in morning or evening; may be increased to 2 mg once daily. Thereafter titrate upwards, if needed, over several weeks, balancing therapeutic benefit with doxazosin-induced postural hypotension

Hypertension: Maximum dose: 16 mg/day

BPH: Goal: 4-8 mg/day; maximum dose: 8 mg/day

Elderly: Initial: 0.5 mg once daily

[Supplied 1 mg, 2 mg, 4 mg, 8 mg tablets]

prazosin  (Minipress ® ) top of page

Mechanism of Action
Prazosin causes a decrease in total peripheral resistance and was originally thought to have a direct relaxant action on vascular smooth muscle. Recent animal studies, however, have suggested that the vasodilator effect of prazosin is also related to blockade of postsynaptic alpha-adrenoceptors.

Oral: Adults:
Hypertension: Initial: 1 mg/dose 2-3 times/day; usual maintenance dose: 3-15 mg/day in divided doses 2-4 times/day; maximum daily dose: 20 mg

Hypertensive urgency: 10-20 mg once, may repeat in 30 minutes

Raynaud's (unlabeled use): 0.5-3 mg twice daily

[Supplied: 1, 2, 5mg capsules]

silodosin - RAPAFLO® top of page

RAPAFLO, an alpha-1 adrenergic receptor antagonist, is indicated for the treatment of the signs and symptoms of benign prostatic hyperplasia (BPH).
RAPAFLO is not indicated for the treatment of hypertension.

8 mg capsules taken orally once daily with a meal.

4 mg capsules taken orally once daily with a meal for those with moderate renal impairment [Creatinine Clearance (CCr) 30-50 mL/min].

Capsules: 8 mg and 4 mg.

tamsulosin  ( Flomax ®  ) top of page

Mechanism of Action
Tamsulosin, an alpha1 adrenoceptor blocking agent, exhibits selectivity for alpha1 receptors in the human prostate. At least three discrete alpha1-adrenoceptor subtypes have been identified: alpha1A, alpha1B and alpha1D; their distribution differs between human organs and tissue. Approximately 70% of the alpha1-receptors in human prostate are of the alpha1A subtype.
Flomax® (tamsulosin hydrochloride) capsules are not intended for use as an antihypertensive drug.

Dosage - Oral: Adults:   BPH:   0.4 mg once daily ~30 minutes after the same meal each day; dose may be increased after 2-4 weeks to 0.8 mg once daily in patients who fail to respond. If therapy is interrupted for several days, restart with 0.4 mg once daily.

Dosage adjustment in renal impairment:
Clcr >/= 10 mL/minute: No adjustment needed
Clcr<10 mL/minute: Not studied

[Supplied: 0.4 mg capsule]

terazosin   (Hytrin ® ) top of page

Mechanism of Action
BPH: The reduction in symptoms and improvement in urine flow rates following administration of terazosin is related to relaxation of smooth muscle produced by blockade of alpha-1 adrenoceptors in the bladder neck and prostate. Because there are relatively few alpha-1 adrenoceptors in the bladder body, terazosin is able to reduce the bladder outlet obstruction without affecting bladder contractility.

HTN: The vasodilatory hypotensive action of terazosin appears to be produced mainly by blockade of alpha-1 adrenoceptors. Terazosin decreases blood pressure gradually within 15 minutes following oral administration.

Oral: Adults:
Hypertension: Initial: 1 mg at bedtime; slowly increase dose to achieve desired blood pressure, up to 20 mg/day; usual dose range (JNC 7): 1-20 mg once daily

Dosage reduction may be needed when adding a diuretic or other antihypertensive agent; if drug is discontinued for greater than several days, consider beginning with initial dose and retitrate as needed; dosage may be given on a twice daily regimen if response is diminished at 24 hours and hypotensive is observed at 2-4 hours following a dose

Benign prostatic hyperplasia: Initial: 1 mg at bedtime, increasing as needed; most patients require 10 mg day; if no response after 4-6 weeks of 10 mg/day, may increase to 20 mg/day

[Supplied 1, 2, 5, 10 mg capsule]


According to 1 study, dosage-conversion from doxazosin to terazosin results in similar or better control of symptoms in most (83%) patients with BENIGN PROSTATIC HYPERPLASIA (BPH). In this study, patients with BPH (n=69) were switched from doxazosin to terazosin according to the following protocol: doxazosin 1 milligram (mg) to terazosin 1 mg, 2 mg to 2 mg, 4 mg to 5 mg, 8 mg to 10 mg, 12 mg to 15 mg, and 16 mg to 20 mg. There were no significant differences in International Prostate Symptom Score (IPSS), blood pressure, pulse, or adverse effects before and after the conversion (p less than 0.05).


National Institutes of Health, U.S. National Library of Medicine, DailyMed Database.
Provides access to the latest drug monographs submitted to the Food and Drug Administration (FDA). Please review the latest applicable package insert for additional information and possible updates.  A local search option of this data can be found here.


Listed dosages are for - Adult patients ONLY. PLEASE READ THE DISCLAIMER CAREFULLY BEFORE ACCESSING OR USING THIS SITE. BY ACCESSING OR USING THIS SITE, YOU AGREE TO BE BOUND BY THE TERMS AND CONDITIONS SET FORTH IN THE DISCLAIMER. GlobalRPH does not directly or indirectly practice medicine or provide medical services and therefore assumes no liability whatsoever of any kind for the information and data accessed through the Service or for any diagnosis or treatment made in reliance thereon.
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