Doxazosin

Alpha-1 adrenergic blocker (non-selective), Benign prostatic hyperplasia treatment, Antihypertensive

Doxazosin

Cardura, Cardura XL

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Summary

Classes

Alpha-1 adrenergic blocker (non-selective), Benign prostatic hyperplasia treatment, Antihypertensive

Pharmacy

Starting dose

IR 1 mg PO at bedtime, titrate weekly; XL 4-8 mg PO daily

Preparations

1, 2, 4, 8 mg IR tablets; 4, 8 mg XL tablets

US FDA Max

16 mg/d (IR); 8 mg/d (XL)

Pharmacology

Routes

Oral

Onset

BP and symptomatic LUTS improvement within 1-2 weeks

Duration

24 hours

Half-life

~22 hours

Bioavailability

~65% (oral)

Pregnancy

Limited data; rarely indicated in pregnancy.^{[citation needed]}

Legal status

Rx-only in US

Purported mechanism

Doxazosin is a non-selective α1 adrenergic receptor antagonist that relaxes vascular smooth muscle (lowering BP) and prostatic/bladder-neck smooth muscle (improving urodynamic flow); unlike tamsulosin, it lacks α1A subtype selectivity, producing more peripheral hypotension and the characteristic first-dose syncope that drives bedtime initiation.▲0▼ ALLHAT (2000) showed the doxazosin arm had significantly more heart failure than chlorthalidone, leading to the general practice of using α1 blockers as later-line antihypertensives rather than first-line. Intraoperative floppy iris syndrome is a recognized class effect.