Doxazosin is a prescription medication belonging to the class of selective α₁‑adrenergic receptor antagonists. It is primarily used in the treatment of hypertension (high blood pressure) and benign prostatic hyperplasia (BPH), a condition characterized by enlargement of the prostate gland that can cause urinary obstruction. The drug is administered orally in tablet form and is available under various brand names, including Cardura.
Chemical and Pharmacological Characteristics
- IUPAC name: (±)-4-[2-(4-Amino-6,7-dimethoxyquinazolin-2-yl)ethoxy]‑2-methoxy‑phenyl‑2‑butyl‑pyridine‑1‑carboxamide
- Molecular formula: C₂₈H₃₂N₄O₅
- Molecular weight: 453.57 g·mol⁻¹
- Physical appearance: White to off‑white crystalline powder, freely soluble in aqueous media.
Doxazosin acts by competitively inhibiting α₁‑adrenergic receptors located on vascular smooth muscle and the prostate. Blockade of these receptors prevents norepinephrine‑induced vasoconstriction, resulting in decreased peripheral vascular resistance and lowered arterial pressure. In the prostate, α₁‑blockade reduces smooth‑muscle tone, improving urinary flow.
Medical Uses
| Indication | Typical Dose Range* | Comments |
|---|---|---|
| Hypertension | 1–8 mg once daily | Dose titrated based on response; often initiated at 1 mg. |
| Benign Prostatic Hyperplasia | 0.4–8 mg once daily | Improves urinary symptoms such as hesitancy and weak stream. |
| Combination therapy for hypertension (e.g., with thiazide diuretics) | Varies | May be used as part of a multi‑drug regimen. |
*Dose ranges reflect standard prescribing information for adult patients; pediatric use is not approved.
Pharmacokinetics
- Absorption: Near‑complete oral absorption with peak plasma concentrations occurring 1–3 hours post‑dose.
- Bioavailability: Approximately 65 % (food does not significantly affect absorption).
- Distribution: Highly protein‑bound (≈98 %) primarily to albumin.
- Metabolism: Minimal hepatic metabolism; the drug is largely excreted unchanged.
- Elimination: Approximately 80 % excreted via the kidneys, the remainder in feces.
- Half‑life: 22–30 hours, supporting once‑daily dosing.
Adverse Effects
Common adverse reactions (≥5 % incidence) include:
- Dizziness or light‑headedness, especially upon standing (orthostatic hypotension).
- Headache.
- Fatigue.
- Nasal congestion.
- Peripheral edema.
Less frequent but clinically significant effects may involve:
- Syncope.
- Tachycardia (reflex).
- Hepatic enzyme elevations.
- Sexual dysfunction (e.g., decreased libido).
Contraindications and Precautions
- Known hypersensitivity to doxazosin or any component of the formulation.
- Caution in patients with severe hepatic impairment, as drug clearance may be reduced.
- Use with caution in patients with a history of orthostatic hypotension, volume depletion, or concurrent use of other antihypertensives that may potentiate blood‑pressure‑lowering effects.
Drug Interactions
- Synergistic hypotensive agents (e.g., other antihypertensives, nitrates) may increase the risk of profound blood pressure reductions.
- Phosphodiesterase‑5 inhibitors (e.g., sildenafil) can enhance hypotensive effects.
- Potassium‑sparing diuretics may exacerbate hyperkalemia.
Clinical Pharmacology
Randomized controlled trials have demonstrated that doxazosin reduces both systolic and diastolic blood pressure compared with placebo. In BPH, the International Prostate Symptom Score (IPSS) typically improves by 30‑40 % after 12 weeks of therapy. Long‑term data suggest cardiovascular benefits when used in combination with other antihypertensives, though the ALLHAT (Antihypertensive and Lipid‑Lowering Treatment to Prevent Heart Attack Trial) highlighted a higher incidence of heart failure in the doxazosin arm compared with chlorthalidone, influencing guideline recommendations.
Regulatory Status and History
- Approval: First approved by the U.S. Food and Drug Administration (FDA) in 1995 for hypertension; BPH indication followed shortly thereafter.
- Patents: Originally patented by Pfizer under the brand name Cardura. Generic formulations have been available since the early 2000s.
- Guidelines: Current hypertension guidelines (e.g., 2023 ACC/AHA) list α₁‑blockers, including doxazosin, as a fourth‑line option after thiazide diuretics, calcium‑channel blockers, ACE inhibitors/ARBs, and beta‑blockers, primarily due to the ALLHAT findings. They remain first‑line for BPH management per urology society recommendations.
Societal and Economic Aspects
Generic doxazosin is widely available worldwide and is listed on many national essential medicines lists. The drug's cost is relatively low compared with newer antihypertensives, contributing to its continued use in low‑resource settings for both hypertension and BPH.
Research Directions
Investigations continue into potential benefits of doxazosin for conditions associated with sympathetic overactivity, such as certain types of heart failure and peripheral arterial disease. However, as of the latest literature (2024), no new indications have received regulatory approval.
References
- United States Food and Drug Administration. Doxazosin (Cardura) Prescribing Information. Revised 2022.
- James PA, et al. “The Fifth Joint National Committee (JNC 5) Report on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.” JAMA. 1993.
- ALLHAT Collaborative Research Group. “Long‑Term Effects of Antihypertensive Drug Treatment on Cardiovascular Morbidity and Mortality.” N Engl J Med. 2002.
- McVary KT, et al. “Efficacy of Doxazosin in Men With Benign Prostatic Hyperplasia.” J Urol. 1998.
This entry reflects current encyclopedic knowledge up to April 2026.