Doxazosin: clinical use

Prescribing considerations

• Assess postural symptoms, blood pressure and falls risk when treatment is initiated or altered.
• Exclude prostate cancer and investigate significant urinary obstruction before treating presumed benign prostate enlargement.
• Use caution in hepatic impairment and relevant acute cardiac conditions; prolonged-release doxazosin is not recommended in severe hepatic impairment.
• Record current or previous alpha-1-blocker exposure before cataract surgery.
• Do not switch between standard-release and XL formulations without medication review and blood-pressure monitoring.

Contraindications and cautions

• Hypersensitivity to doxazosin, other quinazolines or relevant excipients.
• History of orthostatic hypotension.
• For BPH: hypotension, or BPH with upper urinary tract congestion, chronic urinary infection or bladder stones.
• Monotherapy in overflow bladder or anuria, with or without progressive renal insufficiency.
• Doxadura XL: previous gastrointestinal or oesophageal obstruction or reduced gastrointestinal lumen diameter.
• Doxadura XL for hypertension: breastfeeding.

Monitoring

• Blood pressure, including postural measurements where clinically relevant.
• Dizziness, syncope, falls and other symptoms of hypotension.
• Therapeutic response and evidence of urinary retention when used for BPH.
• Liver function when clinically indicated.
• Blood pressure and symptoms after any formulation switch.

Clinical pharmacology

Doxazosin is a selective post-junctional alpha-1-adrenoceptor antagonist. It is highly protein-bound, extensively metabolised by the liver and has a terminal plasma half-life of about 22 hours. Prolonged-release tablets produce a lower peak and smaller peak-to-trough variation than immediate-release tablets.

Formulation and product differences

• The selected standard-release tablet may be divided into equal halves and contains lactose.
• Doxadura XL must be swallowed whole; crushing, chewing or dividing can disrupt prolonged release.
• An empty-looking XL tablet shell may appear in stools and does not necessarily mean the medicine was not released.
• Doxadura XL has additional contraindications relating to gastrointestinal narrowing or obstruction.
• Any formulation switch should be clinician-led with monitoring.

Modified-release tablet

Route: Oral

Strengths: 4 mg

Tablet

Route: Oral

Strengths: 1 mg, 2 mg, 4 mg, 8 mg