Doxazosin ā NZ Medication Guide
š Reviewed by a Registered Pharmacist NZ ā This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Doxazosin?
Doxazosin is an alpha-1 adrenergic receptor antagonist used for the treatment of hypertension and benign prostatic hyperplasia (BPH). This medication is commonly prescribed in New Zealand and is funded by Pharmac for hypertension and BPH.
What is Doxazosin Used For?
Doxazosin is prescribed for hypertension (either alone or in combination with other antihypertensives) and for benign prostatic hyperplasia (BPH), where it helps relax smooth muscle in the prostate and bladder neck to improve urinary flow.
How Does Doxazosin Work?
Doxazosin blocks alpha-1 adrenergic receptors in vascular smooth muscle, causing vasodilation and reducing peripheral resistance ā thereby lowering blood pressure. In BPH, alpha-1 blockade relaxes smooth muscle in the prostate and bladder neck, reducing urinary obstruction and improving flow.
How to Take Doxazosin
Started at a low dose (1 mg) at bedtime to minimise first-dose hypotension. The dose is gradually increased over weeks. Extended-release formulations (Cardura XLĀ®) can be taken in the morning. Swallow tablets whole ā do not crush or chew modified-release tablets.
Common Side Effects of Doxazosin
- Dizziness and light-headedness (especially on standing ā orthostatic hypotension)
- Fatigue
- Headache
- Peripheral oedema (ankle swelling)
- Nasal congestion
- Palpitations
Serious Side Effects ā Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Severe hypotension (particularly with first dose or when combined with other BP medicines)
- Fainting (syncope)
- Intraoperative floppy iris syndrome (if having cataract surgery ā inform your eye surgeon)
- Priapism (prolonged painful erection ā rare but requires urgent medical attention)
Drug Interactions
Doxazosin may interact with other medicines. Always inform your doctor and pharmacist of all medications, supplements, and herbal products you are taking. Key interactions include:
- Other antihypertensive agents (additive hypotension)
- PDE-5 inhibitors (sildenafil, tadalafil ā risk of severe hypotension)
- Verapamil (enhanced hypotension)
New Zealand Prescribing Information
Doxazosin is funded by Pharmac and available as 1 mg, 2 mg, and 4 mg standard tablets, as well as 4 mg and 8 mg extended-release tablets (Cardura XLĀ®). Patients scheduled for cataract surgery must inform their ophthalmologist that they are taking doxazosin, as it can cause intraoperative floppy iris syndrome (IFIS).
Frequently Asked Questions
Why is doxazosin started at night?
The first dose can cause a significant drop in blood pressure (first-dose hypotension) causing dizziness or fainting. Taking it at bedtime means you are lying down when the peak effect occurs, reducing the risk of falls.
Can doxazosin be used for BPH if I don’t have high blood pressure?
Yes. Doxazosin is commonly used for BPH even in patients with normal blood pressure. However, it may cause some lowering of blood pressure and dizziness, so starting with the lowest dose and titrating slowly is important.
ā ļø Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider with any questions you may have regarding a medical condition or medication. In New Zealand, medication availability and funding may vary ā check with Pharmac or your pharmacist for the most current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: