doxazosin

Brand: Cardura

Beers Criteria Prototype Drug

Drug Class: alpha-1 blocker

Drug Family: antihypertensive

Subclass: quinazoline alpha-1 antagonist (long-acting)

Organ Systems: cardiovascular

Mechanism of Action

Selective alpha-1 adrenergic receptor antagonist; vasodilates arteries and veins; also relaxes smooth muscle in prostate and bladder neck.

alpha-1 adrenergic receptor

Absorption	65% oral bioavailability; food does not affect absorption
Distribution	high Vd, lipophilic
Metabolism	extensive hepatic CYP3A4, CYP2D6, CYP2C9
Excretion	fecal 63%, renal 9%
Half-life	22 hours
Onset	1-3 hours
Peak	2-3 hours
Duration	24 hours
Protein Binding	98%
Vd	1.5 L/kg

Drug / Agent	Mechanism	Severity
PDE-5 inhibitors (sildenafil)	severe hypotension — additive vasodilation	major
CYP3A4 inhibitors	increased doxazosin exposure	moderate

First dose at bedtime to minimize orthostatic hypotension
Inform ophthalmologist before cataract surgery (IFIS — pupil dilates poorly, vitreous loss risk)
Tell urologist if on doxazosin for BPH before any pelvic surgery
Avoid in elderly (Beers criteria — hypotension risk)
XL formulation (Cardura XL) for BPH only, not approved for hypertension

ALLHAT trial: doxazosin arm terminated early due to increased HF risk vs chlorthalidone
IFIS (intraoperative floppy iris syndrome) — must inform ophthalmologist preoperatively
Dual indication: hypertension + BPH — useful in male patients with both conditions

Pregnancy avoid

Lactation avoid

Renal Adjustment Not required

Hepatic Adjustment Required

TDM Not required

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