What is Cardura (Doxazosin)?
Cardura (doxazosin) is a long-acting, selective alpha-1 adrenergic receptor blocker primarily used to treat benign prostatic hyperplasia (BPH) and hypertension by reducing smooth muscle tone in the prostate, bladder neck, and peripheral blood vessels. 1
Mechanism of Action
Doxazosin works by selectively blocking alpha-1 adrenoceptors, which are present in high density in the prostatic stroma, prostatic capsule, bladder neck, and peripheral vasculature. 1 This blockade produces two key therapeutic effects:
- In BPH: Decreases urethral resistance by reducing smooth muscle tone in the prostate and bladder neck, thereby relieving bladder outflow obstruction and improving urinary symptoms 1, 2
- In hypertension: Reduces total peripheral resistance through vasodilation without significantly affecting cardiac output or heart rate 2, 3
Formulations and Dosing
Cardura is available in two formulations 1:
- Immediate-release tablets: Doxazosin mesylate in standard formulation
- Extended-release (Cardura XL): Uses GITS (Gastrointestinal Therapeutic System) technology with 4 mg or 8 mg doses, designed for once-daily administration 1, 4
The extended-release formulation provides controlled drug delivery independent of pH or GI motility, achieving stable serum concentrations over 24 hours with reduced peak-to-trough fluctuation. 1, 4 The drug is released gradually through a laser-drilled orifice as water enters the osmotic tablet core, with over 85% released within 12 hours 4.
Clinical Applications
Benign Prostatic Hyperplasia
Doxazosin is recognized in the 2023 European Association of Urology guidelines as an alpha-blocker option for treating male lower urinary tract symptoms (LUTS) associated with BPH. 5 Studies demonstrate:
- Significant improvement in maximum urinary flow rate (Qmax), residual urine volume, IPSS scores, and quality of life 6
- Effective as monotherapy or in combination with antimuscarinics for patients with storage symptoms 5
- In combination therapy with tolterodine, doxazosin showed efficacy in men with symptomatic bladder outlet obstruction and overactive bladder 5
Hypertension
Doxazosin effectively lowers both standing and supine blood pressure throughout a 24-hour dosing interval, with comparable efficacy to atenolol 50-100 mg and other standard antihypertensives. 3, 7
Additional cardiovascular benefits include 2, 3:
- Modest decreases in total cholesterol, LDL cholesterol, and triglycerides
- Small increases in HDL cholesterol and HDL/total cholesterol ratio
- Reduction in left ventricular hypertrophy
- Improved glucose tolerance and insulin sensitivity, particularly beneficial in diabetic patients 8
Important Safety Considerations
Age-Related Hypotension Risk
The incidence of hypotension with Cardura XL appears age-related and significantly more prevalent in patients ≥70 years old (2.9% vs 1.3% in younger patients). 1 This increased risk may relate to:
- 27% increase in maximum plasma concentrations (Cmax) in elderly patients
- 34% increase in area under the curve (AUC) compared to younger patients 1
- Enhanced sensitivity to vasodilatory agents with aging 1
Acute Urinary Retention
The 2021 AUA guidelines recommend prescribing an oral alpha-blocker like doxazosin prior to voiding trial for patients with acute urinary retention related to BPH, with at least 3 days of therapy before attempting trial without catheter. 5
Common Side Effects
Reported adverse effects include 6:
- Headache (10%)
- Fatigue (5%)
- Dizziness (5%)
- Postural hypotension, particularly early in treatment 7
Most side effects are mild to moderate in severity, with excellent overall tolerance in clinical studies. 6
Hepatic Impairment
Cardura XL is not recommended in patients with severe hepatic impairment due to lack of clinical experience, and should be used with caution in mild to moderate hepatic dysfunction. 1
Clinical Pearls
Cardura XL at 4 mg daily represents an effective initial dose for BPH, with 60% of patients achieving adequate blood pressure control at this starting dose. 4 The unique GITS technology minimizes peak-related side effects while maintaining therapeutic efficacy throughout the dosing interval 4.
Doxazosin is particularly suitable for hypertensive patients with concurrent dyslipidemia, type 2 diabetes, or BPH due to its favorable metabolic profile. 4, 8