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Doxazosin, Oral Tablet

Highlights for Doxazosin

  1. Doxazosin oral tablet is available as both a generic and brand-name drug. Brand name: Cardura.
  2. It is used to treat benign prostatic hyperplasia (BPH) and high blood pressure.
  3. Common side effects of doxazosin include dizziness, tiredness, and swelling of your feet, hands, arms, and legs.
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Important warnings

Important warnings

  • Low blood pressure warning: Doxazosin can cause your blood pressure to become low. This may cause dizziness, lightheadedness, and vertigo when you stand up. This is most common with your first dose of medication. The reaction is known as a “first-dose” effect, but it can also occur when your doctor changes your dose. Your doctor will start you on the lowest dose and slowly increase it.
  • Cataract surgery warning: Intraoperative floppy iris syndrome (IFIS) can occur during cataract surgery in people who take or have taken doxazosin. You may not have to stop taking doxazosin prior to your surgery, but you should tell your doctor if you have a cataract surgery planned.

About

What is doxazosin?

Doxazosin oral tablet is a prescription drug that’s available as the brand-name drug Cardura. It’s also available in a generic version. Generic drugs usually cost less. In some cases, generic drugs may not be available in every strength or form as the brand.

It’s also available in both immediate-release and extended-release oral tablets.

Why it's used

Doxazosin is used to treat benign prostatic hyperplasia (BPH) and high blood pressure (immediate-release tablets only). The most up-to-date guidelines for the treatment of high blood pressure don’t recommend the use of doxazosin.

This drug may be used as part of a combination therapy. That means you may need to take it with other drugs.

How it works

Doxazosin belongs to a class of drugs called alpha-1-adrenergic blockers. It works by blocking certain chemicals, which helps to widen blood vessels and relax muscles in your prostate and in your bladder.

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Side effects

Doxazosin side effects

Doxazosin oral tablet is sedating and causes drowsiness. Be careful driving and doing other activities that require you to be alert until you know how it affects you.

Doxazosin may also cause your blood pressure to become low. This may cause dizziness, lightheadedness, and vertigo when you stand up. This is most common with your first dose of medication and is known as a “first-dose” effect. But it can also happen when your doctor changes your dose. Your doctor will start you on the lowest dose of doxazosin and slowly increase it.

Mild side effects may disappear within a few days or a couple of weeks. Talk to your doctor or pharmacist if they’re more severe or don’t go away.

More common side effects

The more common side effects that occur with doxazosin when treating benign prostatic hyperplasia include:

  • low blood pressure
  • dizziness
  • shortness of breath
  • tiredness
  • abdominal pain
  • diarrhea
  • headache
  • swelling of your feet, hands, arms, and legs

The more common side effects that occur when treating high blood pressure include:

  • low blood pressure
  • dizziness
  • headache
  • tiredness
  • nausea
  • runny nose
  • swelling of your feet, hands, arms, and legs

Serious side effects

If you experience any serious side effects, call your doctor right away. If your symptoms are potentially life threatening, or if you think you’re experiencing a medical emergency, call 911. Serious side effects can include:

  • heart problems. Symptoms may include:
    • rapid, pounding, or irregular heartbeat
    • chest pain
  • painful erection that lasts for hours (priapism)
  • severe allergic reaction. Symptoms may include:
    • wheezing
    • chest tightness
    • itching
    • swelling of your face, lips, tongue, or throat
    • hives
  • breathing problems. Symptoms may include:
    • shortness of breath

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.

Interactions

Doxazosin may interact with other medications

Doxazosin oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Examples of drugs that can cause interactions with promethazine are listed below.

Drugs that inhibit CYP3A4 enzymes

Doxazosin is broken down by the CYP3A4 enzyme—a common enzyme that processes drugs. Medications that block it from working or over work it to increase its effects, will change the level of doxazosin in your body. It’s important to let your doctor know all the medications you’re taking so they can monitor the effect of doxazosin when taken with these medications.

Examples include:

  • CYP3A4 Inhibitors
    • Antifungals (Azole antifungals): Fluconazole, ketoconazole, voriconazole
    • HIV medications (protease inhibitors): ritonavir, saquinavir, indinavir
    • Macrolide antibiotics: clarithromycin, telithromycin, erythromycin
    • Grapefruit juice
  • CYP3A4 Inducers
    • Antiseizure: fosphenytoin, phenytoin, carbamazepine
    • HIV medications (non-nucleoside reverse transcriptase inhibitors): efavirenz, etravirine
    • St. John’s wort

Blood pressure medications

  • drugs to lower your blood pressure. Combining doxazosin with any drug that lowers your blood pressure can increase your risk for lowering your blood pressure too much. Examples are:
    • aldosterone antagonists, such as: spironolactone, eplerenone
    • angiotensin-converting enzyme inhibitors (ACEIs), such as: benazepril, lisinopril, enalapril, fosinopril
    • angiotensin receptor blockers (ARBs), such as: losartan, candesartan, valsartan
    • beta-blockers, such as: atentolol, bisoprolol, metoprolol, propranolol
    • calcium channel blockers (DHP), such as: amlodipine, nifedipine, nicardapine,
    • calcium channel blockers (non DHP) such as: diltiazem, verapamil
    • centrally-acting adrenergic agents, such as: clonidine, guanfacine, methyldopa
    • direct renin inhibitors, such as: aliskiren
    • diuretics (loop and thiazide/thiazide-like): amiloride, chlorthalidone, furosemide, metolazone
    • vasodilators: hydralazine, minoxidil
    • nitrates, such as: isosorbide mononitrate, isosorbide dinitrate, nitroglycerin transdermal patch
  • drugs that increase your blood pressure. Combining doxazosin with drugs that increase your blood pressure can cancel the effects of both medications. Examples are:
    • symphathomimetics (decongestants): pseudoephedrine, oxymetazoline, phenylephrine
    • erythropoiesis-stimulating agents (red blood cell production stimulators): darbepoetin alfa, epoetin alfa
    • contraceptives (birth control): ethinyl estradiol, ethinyl estradiol/levonorgestrel
  • drugs to treat pulmonary arterial hypertension. Combining doxazosin with these drugs can increase your risk of low blood pressure. Examples are:
    • endothelin receptor blockers, such as: ambrisentan, bosentan, macitenan
    • phosphodiaesterase-5 (PDE-5) blockers, such as: sildenafil, tadalafil
    • nitric oxide

Erectile dysfunction drugs

  • phosphodiaesterase-5 (PDE-5) inhibitors. Combining doxazosin with PDE-5 inhibitors can increase the blood pressure-lowering effects of doxazosin and increase your risk of side effects. An example is:
    • tadalafil. Combining these drugs can cause a serious drop in your blood pressure.

Attention deficit hyperactivity disorder (ADHD) drug

  • methylphenidate

Combining this drug with doxazosin can lower the effect of doxazosin. This may cause your blood pressure to stay too high.

Parkinson’s disease drugs

Combining these drugs with doxazosin can increase your risk of low blood pressure when standing:

  • levodopa
  • MAO inhibitors (MAOIs). Examples are:
    • isocarboxazid (Marplan)
    • phenelzine (Nardil)
    • tranylcypromine (Parnate)
    • selegiline (Emsam, Eldepryl, Zelapar)

Cancer drugs

Combining these medications with doxazosin increases your risk of low blood pressure.

  • amifostine. Your doctor may stop your doxazosin 24 hours before giving you amifostine. If you can’t stop taking doxazosin, you shouldn’t take amifostine.
  • obinutuzumab. Your doctor may stop your doxazosin 12 hours before giving you obinutuzumab. You shouldn’t take doxazosin for 1 hour after taking obinutuzumab.
  • rituximab

Hepatitis C drug

  • boceprevir

Combining boceprevir with doxazosin will increase the levels of doxazosin and increase your risk of side effects. Don’t take these medications together.

Herbal medications

  • yohimbine. Combining this with doxazosin can lower the effect of doxazosin and cause your blood pressure to stay too high.
  • Herbs that can increase your blood pressure. Combining these with doxazosin can lower the effect of doxazosin and cause your blood pressure to stay too high.
  • Herbs that can lower your blood pressure. Combining these with doxazosin can increase your risk of low blood pressure.

Antidepressant

  • duloxetine

Combining this with doxazosin can increase your risk of low blood pressure when standing up.

Seizure drugs

  • barbiturates, such as:
    • Phenobarbital
    • Pentobarbital
    • Primidone

Combining these with doxazosin can increase your risk of low blood pressure.

Intermittent claudication drug

  • pentoxifylline

Combining this with doxazosin can increase your risk of low blood pressure.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

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Other warnings

Doxazosin warnings

Doxazosin oral tablet comes with several warnings.

Allergy warning

Doxazosin can cause a severe allergic reaction. Symptoms may include:

  • trouble breathing
  • swelling of your throat or tongue
  • hives

Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal.

Warnings for people with certain health conditions

For people with liver problems: Doxazosin is broken down by your liver. If you have liver problems, you may have an increased risk of side effects.

For people having cataract surgery: Intraoperative floppy iris syndrome (IFIS) can occur during cataract surgery in people who take or have taken doxazosin. You may not have to stop taking doxazosin prior to your surgery, but you should tell your doctor if you have a cataract surgery planned.

Warnings for other groups

For pregnant women: Doxazosin is a category C pregnancy drug. That means two things:

  1. Research in animals has shown adverse effects to the fetus when the mother takes the drug.
  2. There haven’t been enough studies done in humans to be certain how the drug might affect the fetus.

Tell your doctor if you’re pregnant or plan to become pregnant. Doxazosin should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

For women who are nursing: Doxazosin passes through breast milk. You and your doctor may need to decide whether you’ll take this medication or breastfeed.

For Seniors: This medication shouldn’t be used to treat high blood pressure in people aged 65 years and older. If you’re 65 or older, you’re at increased risk of having low blood pressure when you stand up. This can lead to dizziness and lightheadedness.

For Children: The safety and effectiveness of doxazosin haven’t been established in people younger than 18 years old for treating benign prostatic hyperplasia (BPH).

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Dosage

How to take doxazosin

This dosage information is for doxazosin oral tablet. All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

Forms, strengths, and dosage for benign prostatic hyperplasia

Generic: Doxazosin

  • Form: Oral immediate-release tablet
  • Strength: 1 mg, 2 mg, 4 mg, and 8 mg
  • Form: Oral extended-release tablet
  • Strength: 4 mg and 8 mg

Adult Dosage (ages 18–64 years)

  • Extended-release tablet:
    • The starting dose is 4 mg per day with breakfast.
    • Your doctor may increase your dose to a maximum of 8 mg per day in 3 to 4 weeks after starting the medication.
    • When switching from immediate-release tablets to extended-release tablets: You may be started on 4 mg per day. Before you start taking the extended-release tablet, don’t take your last evening dose of the immediate-release tablet.
  • Immediate-release tablet:
    • The starting dose is 1 mg per day in the morning or evening.
    • Your doctor may increase your dose by 2 mg every 1–2 weeks, up to a maximum of 8 mg per day.

Child Dosage (ages 0–17 years)

A safe and effective dose hasn’t been established for this age group.

Senior Dosage (ages 65 years and older)

Your body may process this drug more slowly. Your doctor may start you on a lowered dose so that too much of this drug doesn’t build up in your body. Too much of the drug in your body can be toxic.

Forms, strengths, and dosage for high blood pressure

Generic: Doxazosin 

  • Form: Oral immediate-release tablet
  • Strength: 1 mg, 2 mg, 4 mg, and 8 mg

Adult Dosage (ages 18–64 years)

  • The starting dose is 1 mg per day.
  • Based on your blood pressure, your doctor may increase your dose 2 mg at a time to a maximum dose of 16 mg per day.

Child Dosage (ages 0–17 years)

A safe and effective dose hasn’t been established for this age group.

Senior Dosage (ages 65 years and older)

Your body may process this drug more slowly. Your doctor may start you on a lowered dose so that too much of this drug doesn’t build up in your body. Too much of the drug in your body can be toxic.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.

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Take as directed

Take as directed

Doxazosin oral tablet is a long-term drug treatment. It comes with risks if you don't take it as prescribed.

If You Don't Take It At All: Your symptoms may not improve or they may get worse over time.

If You Stop Taking It Suddenly: If your condition improved while taking the medication regularly and you stop taking doxazosin suddenly, your symptoms may come back.

If You Don't Take It on Schedule: You may not see a full benefit of this medication. If you double up your dose or take it too close to your next scheduled time, you may be at higher risk of experiencing serious side effects.

What to Do If You Miss a Dose: If you miss a dose, take it as soon as you can. However, if it’s just a few hours until your next dose, wait and take a single dose.

Never try to catch up by taking two doses at once. This could result in toxic side effects

How to Tell If the Drug Is Working: You may be able to tell this drug is working for benign prostatic hyperplasia (BPH) if you have an easier time urinating and experience fewer symptoms of obstruction and irritation.

You may be able to tell it’s working for high blood pressure if your blood pressure is lower. High blood pressure doesn’t often have symptoms, so you may need to take a blood pressure test to know if your pressure is lower.

Important considerations

Important considerations for taking doxazosin

Keep these considerations in mind if your doctor prescribes doxazosin oral tablet for you.

General

  • Take the extended-release tablet with breakfast.
  • Take the extended-release tablet in the morning.
  • Don’t cut or crush the extended-release form. You can cut or crush the immediate-release tablet.
  • Not every pharmacy stocks this drug, so call ahead.

Storage

Store in temperatures from 59–86°F (15–30°C). Keep drugs away from areas where they could get wet, such as bathrooms. Store them away from moisture and damp locations.

Refill

A prescription for this medication is refillable. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry it with you or in your carry-on bag.
  • Don’t worry about airport X-ray machines. They can’t hurt this medication.
  • You may need to show your pharmacy’s preprinted label to identify the medication. Keep the original prescription-labeled box with you when traveling.

Self-management

If you’re taking this drug for high blood pressure, your doctor may recommend getting a blood pressure monitor. You may keep it at home to check your blood pressure on a regular basis in between clinic visits.

Clinical Monitoring

If you’re taking this drug for high blood pressure, your doctor will check your blood pressure at every visit to make sure the medication is working correctly. Your doctor may increase your dose if your blood pressure is too high or lower your dose if your blood pressure is too low.

Insurance

Many insurance companies will require a prior authorization before they approve the prescription and pay for doxazosin.

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Alternatives

Are there any alternatives?

There are other drugs available to treat your condition. Some may be more suitable for you than others. Talk to your doctor about possible alternatives

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

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