Doxazosin

Doxazosin is a selective alpha-1 adrenoceptor antagonist used in the treatment of hypertension and the symptomatic management of benign prostatic hyperplasia (BPH).

It is effective in lowering blood pressure and relieving urinary symptoms associated with prostate enlargement.

In hypertension, doxazosin works by blocking alpha-1 receptors on vascular smooth muscle, preventing noradrenaline from causing vasoconstriction.

This results in peripheral vasodilation and a reduction in peripheral vascular resistance, leading to lower blood pressure.

In BPH, the drug relaxes smooth muscle in the prostate gland and bladder neck, reducing the obstruction to urinary flow caused by the enlarged prostate.

Doxazosin is available as standard tablets and as a modified-release (gastrointestinal therapeutic system or GITS) formulation.

The modified-release formulation provides a more gradual onset of action and a smoother plasma concentration profile, which may reduce the incidence of first-dose hypotension.

Unlike some other antihypertensives, doxazosin has a favourable metabolic profile, with beneficial effects on lipid levels.

Take doxazosin by mouth once daily. The first dose should ideally be taken at bedtime to minimise the risk of first-dose hypotension (a sudden drop in blood pressure on standing).

Subsequent doses can be taken at any time of day. Modified-release tablets should be swallowed whole with a glass of water; do not crush, chew, or break them.

Continue taking doxazosin as directed, even if you feel well.

For hypertension: start with 1 mg once daily, increasing at intervals of 1 to 2 weeks to 2 mg, then 4 mg, and up to a maximum of 16 mg daily as needed.

For BPH: start with 1 mg once daily, increasing to 2 mg, then 4 mg, and up to 8 mg daily. The modified-release formulation starts at 4 mg once daily and may be increased to 8 mg.

Dose titration should be guided by blood pressure and symptom response.

Common (1 in 10 to 1 in 100): dizziness, headache, fatigue, asthenia, oedema, postural hypotension, rhinitis.

Uncommon (1 in 100 to 1 in 1,000): nausea, abdominal pain, dry mouth, vertigo, somnolence, urinary incontinence, tachycardia.

Rare (1 in 1,000 to 1 in 10,000): syncope, impotence, priapism, hepatitis, cholestasis, thrombocytopenia, leucopenia, bronchospasm.

Very rare (less than 1 in 10,000): urticaria, intraoperative floppy iris syndrome during cataract surgery. First-dose dizziness is minimised by starting at a low dose and taking it at bedtime.

First-dose hypotension may cause dizziness, lightheadedness, or fainting, particularly at the start of treatment or after dose increases. Patients should be cautioned about standing up quickly.

Use with caution in patients with hepatic impairment.

Patients undergoing cataract surgery should inform their ophthalmologist of current or previous alpha-blocker use, as intraoperative floppy iris syndrome has been associated with these drugs.

Doxazosin may cause postural hypotension when combined with other antihypertensives, phosphodiesterase-5 inhibitors, or alcohol.

Doxazosin is contraindicated in patients with known hypersensitivity to doxazosin, other quinazolines, or any of the excipients.

It is contraindicated in patients with a history of orthostatic hypotension and (for BPH monotherapy) in patients with overflow incontinence or anuria.

The modified-release formulation should not be used in patients with gastrointestinal obstruction.