What is doxazosin?

Doxazosin is an alpha-adrenergic (AL-fa ad-ren-ER-jik) blockers. It relaxes your veins and arteries so that blood can more easily pass through them. It also relaxes the muscles in the prostate and bladder neck, making it easier to urinate.

Doxazosin is used to treat hypertension (high blood pressure), or to improve urination in men with benign prostatic hyperplasia (enlarged prostate).

The extended-release form of doxazosin (Cardura XL) is for use only in treating benign prostatic hyperplasia and should not be used to treat hypertension.

Important information

Doxazosin can affect your pupils during cataract surgery. Tell your eye surgeon ahead of time that you are using doxazosin. Do not stop using this medicine before surgery unless your surgeon tells you.

You should not use this medication if you are allergic to doxazosin or similar medicines such as alfuzosin (Uroxatral), prazosin (Minipress), silodosin (Rapaflo), tamsulosin (Flomax), or terazosin (Hytrin). Doxazosin may cause dizziness or fainting, especially when you first start taking it or when you start taking it again. Be careful if you drive or do anything that requires you to be alert. Avoid standing for long periods of time or becoming overheated during exercise and in hot weather. Avoid getting up too fast from a sitting or lying position, or you may feel dizzy.

Tell your doctor about all other medications you use, especially other blood pressure medications including diuretics (water pills).

Before taking this medicine

You should not use this medicine if you are allergic to doxazosin or similar medicines such as alfuzosin (Uroxatral), prazosin (Minipress), silodosin (Rapaflo), tamsulosin (Flomax), or terazosin (Hytrin).

To make sure doxazosin is safe for you, tell your doctor if you have:

• a blockage in your digestive tract (stomach or intestines);

• severe constipation;

• liver disease; or

• low blood pressure.

Doxazosin can affect your pupils during cataract surgery. Tell your eye surgeon ahead of time that you are using this medication. Do not stop using this medicine before surgery unless your surgeon tells you to.

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

It is not known whether doxazosin passes into breast milk or if it could harm a nursing baby. You should not breast-feed while using this medicine.

How should I take doxazosin?

Take doxazosin exactly as prescribed by your doctor. Follow all directions on your prescription label. Your doctor may occasionally change your dose. Do not use this medicine in larger or smaller amounts or for longer than recommended.

Doxazosin lowers blood pressure and may cause dizziness or fainting, especially when you first start taking it, or when you start taking it again.

You may feel very dizzy when you first wake up. Be careful when standing or sitting up from a lying position.

Call your doctor if you have severe dizziness or feel like you might pass out.

While using doxazosin, your blood pressure or prostate may need to be checked often.

If you stop taking doxazosin for any reason, ask your doctor before you start taking it again. You may need a dose adjustment.

If you are being treated for high blood pressure, keep using this medicine even if you feel well. High blood pressure often has no symptoms. You may need to use blood pressure medicine for the rest of your life.

Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

If you miss your doses for several days in a row, call your doctor before restarting the medication. You may need a lower dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include extreme dizziness or fainting.

What should I avoid while taking doxazosin?

Doxazosin may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

To prevent dizziness, avoid standing for long periods of time or becoming overheated during exercise and in hot weather.

Avoid getting up too fast from a sitting or lying position, or you may feel dizzy. Get up slowly and steady yourself to prevent a fall.

Drinking alcohol with this medicine can cause side effects.

Doxazosin side effects

Get emergency medical help if you have signs of an allergic reaction to doxazosin: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

• a light-headed feeling, like you might pass out;

• severe ongoing stomach pain or bloating;

• new or worsening chest pain;

• trouble breathing; or

• a penis erection that is painful or lasts 4 hours or longer.

Common doxazosin side effects may include:

• low blood pressure, dizziness;

• drowsiness;

• headache; or

• feeling weak or tired.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Doxazosin dosing information

Usual Adult Dose for Hypertension:

Initial dose: 1 mg orally once a day.
Maintenance dose: 1 to 16 mg orally once a day.

Usual Adult Dose for Benign Prostatic Hyperplasia:

Initial dose:
Immediate-release: 1 mg orally once a day.
Extended-release: 4 mg orally once a day with breakfast

Maintenance dose:
Immediate-release: 1 to 8 mg orally once a day.
Extended-release: 4 to 8 mg orally once a day with breakfast. Depending on the patient's symptomatic response and tolerability, the dose may be increased to 8 mg (the maximum recommended dose). The recommended titration interval is 3 to 4 weeks.

If switching from immediate-release doxazosin tablets to extended-release tablets, therapy should be initiated with the lowest dose (4 mg once daily). Prior to starting therapy with doxazosin extended-release tablets, the final evening dose of immediate-release tablets should not be taken. If doxazosin extended-release tablets are discontinued for several days, therapy should be restarted using the 4 mg once daily dose.

Usual Geriatric Dose for Hypertension:

Initial dose: 0.5 mg orally once a day.

What other drugs will affect doxazosin?

Tell your doctor about all your current medicines and any you start or stop using, especially:

• an antibiotic;

• an antidepressant;

• medicine to treat HIV or AIDS; or

• sildenafil (Viagra) or other erectile dysfunction medicines.

This list is not complete. Other drugs may interact with doxazosin, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use doxazosin only for the indication prescribed.