Overview
Doxazosin is an alpha-1 adrenergic receptor antagonist used primarily for the treatment of hypertension and benign prostatic hyperplasia (BPH). It works by relaxing blood vessels and prostate/urethral smooth muscle, reducing blood pressure and improving urinary flow. It is available in oral tablet formulations.
Mechanism of Action
Doxazosin selectively blocks postsynaptic alpha-1 adrenergic receptors, leading to vasodilation of peripheral blood vessels (reducing blood pressure) and relaxation of smooth muscle in the prostate and bladder neck (improving urinary symptoms in BPH).
Indications
- Treatment of hypertension
- Symptomatic treatment of benign prostatic hyperplasia (BPH)
Common Doses
- 1 mg
- 2 mg
- 4 mg
- 8 mg
Dosage
For hypertension: Initial dose 1 mg once daily, may be increased to 2 mg, then 4 mg, and up to 16 mg daily based on response. For BPH: Initial dose 1 mg once daily, may be increased to 2 mg, 4 mg, and 8 mg daily. Doses should be taken at bedtime to minimize orthostatic hypotension.
Contraindications
- Hypersensitivity to doxazosin, other quinazolines (e.g., prazosin, terazosin), or any components of the formulation
Side Effects
- Dizziness
- Fatigue
- Headache
- Orthostatic hypotension
- Edema
- Somnolence
- Nausea
Interactions
- Other antihypertensive agents (additive hypotensive effects)
- Phosphodiesterase-5 inhibitors (e.g., sildenafil) may increase hypotensive effects
- CYP3A4 inhibitors may increase doxazosin concentrations
Counseling Points
- Take first dose at bedtime to minimize dizziness
- Rise slowly from sitting/lying position to prevent dizziness
- Do not drive or operate machinery if experiencing dizziness
- Report fainting or severe dizziness to healthcare provider
- Do not stop taking abruptly without medical advice