Doxazosin

1. Introduction

Doxazosin is an alpha-1 adrenergic receptor blocker used to treat hypertension and symptoms of benign prostatic hyperplasia (BPH). It works by relaxing the smooth muscle in blood vessels and the bladder neck, improving blood flow and urinary flow. Its dual benefits make it a valuable medication for patients with both hypertension and BPH.

2. Indications

  • Approved Indications:
    • Hypertension (as monotherapy or in combination with other antihypertensives).
    • Benign prostatic hyperplasia (BPH) to improve urinary symptoms.
  • Off-Label Uses:
    • Ureteral stones (to improve stone passage by relaxing ureteral smooth muscle).

3. Dosage

  • Adults (Hypertension):
    • Initial dose: 1 mg once daily.
    • Maintenance dose: 2–16 mg daily, adjusted based on response.
  • Adults (BPH):
    • Initial dose: 1 mg once daily.
    • Maintenance dose: 2–8 mg once daily, adjusted based on symptoms.
  • Elderly:
    • Start with 0.5–1 mg once daily due to increased sensitivity to orthostatic hypotension.

4. Administration

  • Take orally, with or without food.
  • Extended-release tablets should be swallowed whole and not crushed or chewed.
  • Take the first dose at bedtime to reduce the risk of dizziness or fainting due to the “first-dose effect.”

5. Forms Available

  • Immediate-release tablets: 1 mg, 2 mg, 4 mg.
  • Extended-release tablets: 4 mg, 8 mg.

6. Side Effects

6.1. Common Side Effects

  • Dizziness.
  • Fatigue.
  • Headache.
  • Postural hypotension (low blood pressure upon standing).

6.2. Less Common Side Effects

  • Nausea.
  • Oedema (swelling).
  • Nasal congestion.

6.3. Rare but Serious Side Effects

  • Syncope (fainting), particularly after the first dose or dose increases.
  • Priapism (prolonged, painful erection).
  • Hepatotoxicity (very rare).

7. Warnings

  • First-Dose Hypotension: Doxazosin can cause a significant drop in blood pressure after the first dose or dose increases, leading to dizziness or fainting.
  • Orthostatic Hypotension: Patients should be cautious when standing up quickly, especially during initial treatment.
  • Cataract Surgery Complications: Risk of intraoperative floppy iris syndrome (IFIS) during cataract surgery in patients previously treated with alpha-blockers.

8. Precautions

  • Use cautiously in patients with a history of orthostatic hypotension or syncope.
  • Avoid in patients with severe liver impairment, as metabolism of the drug is primarily hepatic.
  • Monitor for symptoms of fluid retention, especially in patients with heart failure.

9. Interactions

  • Drug-Drug Interactions:
    • Antihypertensives (e.g., beta-blockers, ACE inhibitors): Additive hypotensive effect.
    • PDE5 inhibitors (e.g., sildenafil, tadalafil): Increased risk of significant hypotension.
    • NSAIDs: May reduce the antihypertensive effect.
  • Drug-Food Interactions:
    • No significant food interactions, but taking with food may reduce gastrointestinal discomfort.

10. Monitoring Parameters

  • Blood pressure (especially after the first dose or dose adjustments).
  • Symptom relief in BPH (e.g., improved urinary flow).
  • Signs of dizziness, syncope, or fatigue.

11. Use in Children

  • Not recommended due to a lack of safety and efficacy data in paediatric populations.

12. Use in Pregnancy

  • Category C: Use only if the potential benefit outweighs the risks, as safety data in pregnancy are limited.

13. Use in Elderly

  • Use cautiously due to an increased risk of postural hypotension and dizziness. Start with the lowest possible dose and titrate slowly.

14. Use in Kidney Disease

  • No specific dose adjustments are required, as doxazosin is not significantly renally excreted.

15. Use in Liver Disease

  • Use with caution in patients with hepatic impairment, as doxazosin is metabolised in the liver. Avoid in severe liver dysfunction.

16. Patient Counselling Points

  • Take the first dose at bedtime to minimise dizziness or fainting (first-dose effect).
  • Stand up slowly after sitting or lying down to reduce the risk of dizziness.
  • Report symptoms such as prolonged erections (lasting more than 4 hours), severe dizziness, or fainting immediately.
  • Continue taking doxazosin regularly to maintain its benefits, even if symptoms improve.
  • Inform your doctor if you are undergoing cataract surgery, as doxazosin may affect the procedure.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
CarduraPfizer$30–50 (30 tablets, 4 mg)
CarduranPfizer$20–40 (30 tablets, 2 mg)
Generic DoxazosinVarious$10–25 (30 tablets, 4 mg)

18. FAQs (15 Questions)

  1. What is doxazosin used for?
    It is used to treat high blood pressure and symptoms of benign prostatic hyperplasia (BPH).
  2. How does doxazosin work?
    It relaxes smooth muscle in blood vessels and the prostate, improving blood flow and urinary symptoms.
  3. What are the common side effects of doxazosin?
    Common side effects include dizziness, fatigue, headache, and postural hypotension.
  4. How should doxazosin be taken?
    Take it once daily, preferably at bedtime, with or without food.
  5. What should I do if I miss a dose?
    Take it as soon as you remember, unless it’s close to the next dose. Do not double the dose.
  6. Can doxazosin cause low blood pressure?
    Yes, especially after the first dose or during dose increases.
  7. Can I drink alcohol while taking doxazosin?
    Alcohol may enhance dizziness or hypotension and should be limited.
  8. Is doxazosin safe for elderly patients?
    Yes, but elderly patients are more prone to dizziness and hypotension, so doses should be started low and increased gradually.
  9. Can doxazosin be taken with other antihypertensives?
    Yes, but the combination may increase the risk of low blood pressure. Monitor carefully.
  10. Can doxazosin be used during pregnancy?
    It should only be used if the potential benefits outweigh the risks, as safety in pregnancy is not well established.
  11. What should I do if I experience dizziness or fainting?
    Sit or lie down immediately and inform your doctor if symptoms persist.
  12. Does doxazosin help with kidney stones?
    It is sometimes used off-label to improve stone passage by relaxing the ureter.
  13. How long does it take for doxazosin to work?
    Blood pressure effects are seen within a few hours, while urinary symptoms may improve within a few days to weeks.
  14. Can doxazosin cause priapism?
    Rarely, it can cause prolonged, painful erections, which require immediate medical attention.
  15. How should doxazosin be stored?
    Store at room temperature, away from moisture and heat.