Hydralazine dosage, forms, and strengths

Medically reviewed by Ashley Wong, Pharm. D.
Licensed Pharmacist
Updated Jan 13, 2025  •  Published Jan 13, 2025
Datos Verificados
In this article:

Key takeaways

  • Hydralazine is a niche blood pressure medication used for emergency or uncommon situations.

  • Doses are either injected by a healthcare provider or taken as tablets four times daily.

  • Tablets can be taken with or without food but must be taken the same way each time.

Hydralazine is a generic prescription blood pressure drug that’s been in use since 1953. Since then, many more effective and safer blood pressure drugs have come on the market, so hydralazine is used for uncommon or emergencies. When used, hydralazine tablets several times a day. Hydralazine can cause serious heart problems and other complications, so doctors carefully monitor treatment.

Hydralazine forms and strengths

Hydralazine is available in two dosage forms: tablets and injections. 

  • Tablets: 10 mg, 25 mg, 50 mg, 100 mg

  • Injection: 20 mg/mL

Hydralazine dosage for adults

Hydralazine is an older but powerful drug that lowers blood pressure and stimulates the heart. Most people with controlled hypertension will never take the drug. Those whose blood pressure is not controlled by combinations of other drugs may have hydralazine added to their treatment. Doctors also use it in blood pressure emergencies or treat heart failure.

Hydralazine is not safe for everyone. Anyone with known allergies cannot take the drug. Other contraindications include coronary artery disease (CAD) and mitral valvular rheumatic heart disease, a complication of untreated or undertreated strep infections.

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Hydralazine dosage chart
Indication Starting dosage Standard dosage Maximum dosage
High blood pressure 10 mg tablet taken 4 times daily OR 10–20 mg intravenous injection every 4-6 hours OR 10–50 mg intramuscular injection every 4-6 hours 10–50 mg tablet taken 4 times daily OR 10–20 mg intravenous injection every 4-6 hours OR 10–50 mg intramuscular injection every 4-6 hours Oral: 300 mg per day Injection: determined by your healthcare provider
Heart failure (off-label) 25–50 mg tablet taken 3-4 times daily 25–50 mg tablet taken 3-4 times daily 300 mg/day
High blood pressure emergency 20–40 mg intravenous or intramuscular injection  20–40 mg intravenous or intramuscular injection  Not specified
High blood pressure emergency during pregnancy (preeclampsia) 5 mg intravenous or intramuscular injection 5 mg intravenous or intramuscular injection, then 5–10 mg intravenously every 20–40 minutes 20 mg cumulative dose

Hydralazine dosage for hypertension

Although hydralazine is one of the first drugs developed to treat high blood pressure, it’s no longer used as a first-line therapy. Doctors add it to a patient’s drug regimen when one or more other antihypertensive drugs or diuretics aren’t working. 

Hydralazine is a peripheral vasodilator. It widens small arteries of the circulatory system, reducing blood pressure in the arteries. Hydralazine also stimulates the heart to beat faster and stronger and increases water and sodium retention. These are usually effects doctors don’t want to see happen in hypertensive patients.

Though hydralazine is used rarely for controlled hypertension, healthcare professionals commonly use it in pregnant women with acute high blood pressure or preeclampsia. Current guidelines recommend hydralazine, labetalol, or nifedipine as first-line treatments. If blood pressure is low enough, women can take tablets at home, but the preferred treatment is nifedipine. For severe hypertension and preeclampsia, hydralazine is often the first choice (see “Hydralazine for severe hypertension” below).

For standard hypertension, prescribers start with an initial dose of 10 mg taken four times daily. After a few days, doses increase to 25 mg four times daily and then to 50 mg four times daily. However, prescribers will monitor therapy and reduce the dose to the lowest effective dose.

Intravenous and intramuscular injections are used when people can’t take tablets or in emergencies.

  • Standard dosage for hypertension: 10–50 mg tablet taken four times daily

  • Maximum dosage for hypertension: 300 mg daily

Hydralazine dosage for hypertensive crisis

When blood pressure rises above 180/120 mmHg, that’s a medical emergency or “hypertensive crisis.” Severe hypertension can rapidly lead to a heart attack, stroke, and organ damage. 

Guidelines advise intravenous or intramuscular injections of uncommon blood pressure medications such as labetalol, hydralazine, esmolol, nicardipine, and urapidil. These aren’t drugs most people buy in a pharmacy. Injections will continue until blood pressure is brought under control. 

Severe hypertension in pregnant women is defined as a blood pressure exceeding 160/110 mmHg. It, too, is a medical crisis. Guidelines recommend using intravenous hydralazine or labetalol and oral nifedipine. 

  • Standard dosage for hypertensive crisis: 20–40 mg intravenous or intramuscular injection repeated as necessary

  • Standard dosage for urgent blood pressure control in pregnancy: 5 mg intravenous or intramuscular injection, then 5–10 mg intravenously every 20–40 minutes

  • Maximum dosage for urgent blood pressure control in pregnancy: 20 mg total

Hydralazine dosage for heart failure

The FDA has not approved hydralazine as a heart failure treatment, but it’s used off-label for this purpose in certain situations. Hydralazine both lowers blood pressure and increases the amount of blood that flows out of the heart.

Guidelines recommend a combination of hydralazine and isosorbide dinitrate, a drug that widens blood vessels, be used in certain African-American heart failure patients or heart failure patients who can’t take first-line treatments for heart failure.

  • Standard dosage for heart failure: 25–50 mg tablet taken three to four times daily

Hydralazine dosage for children

Hydralazine has not been approved for use in pediatric patients.

Hydralazine dosage restrictions

Hydralazine does not require dosage modifications for people with hepatic impairment (liver problems). Though dosage reductions are not required in the FDA-approved drug information, people with renal impairment (kidney disease) may be asked to space out their doses.

  • Renally impaired patients:

    • Moderate renal impairment (creatinine clearance 10-50 mL/min): administer doses every eight hours

    • Severe renal impairment (creatinine clearance < 10 mL/min): administer doses every eight to 24 hours depending on patient response

Hydralazine dosage for pets 

Veterinarians primarily use hydralazine in cats and dogs to treat heart failure. They may also use it to treat high blood pressure, but it’s not a first choice. For heart failure, the standard dosage of hydralazine in dogs is 0.5–3 mg per kilogram of body weight given every eight hours. It’s the same for cats, but the starting dose will be lower.

How to take hydralazine

  • Take this medication as prescribed. The dose may change several times at first.

  • Doses are taken three to four times daily. Use an alarm or smartphone to help you remember to take them.

  • Take doses at the same time every day.

  • Hydralazine may be taken with or without food. However, take the pill the same way each time.

  • Swallow the tablet whole with a drink of water.

  • Store hydralazine tablets at room temperature out of the reach of children.

Hydralazine dosage FAQs

How long does it take hydralazine to work?

Hydralazine lowers blood pressure shortly after a dose is swallowed and hits its peak effects one or two hours later.

How long does hydralazine stay in your system?

Hydralazine has a half-life of three to seven hours, so it will take anywhere from half a day to an entire day to clear a dose from the body.

What happens if I miss a dose of hydralazine?

Ask the prescriber what to do about a missed dose of hydralazine. Doses are taken four hours apart and should be taken at the same time each day. 

How long can you take hydralazine?

Hydralazine is a niche blood pressure treatment. Except when used for heart failure, it’s usually a limited treatment. If you and your healthcare provider determine it’s safe for you to take, you’ll likely take hydralazine long-term. 

How do I stop taking hydralazine?

The sudden discontinuation of hydralazine will not cause withdrawal. However, blood pressure may increase dramatically. This can increase your risk of heart problems, such as heart attack or chest pain. Do not stop taking hydralazine until talking with the prescriber.

A prescriber may choose to stop hydralazine in some cases, including allergic reactions, side effects, or just a failure to work. About 5% to 10% of people taking hydralazine experience lupus-like symptoms, a condition called hydralazine-induced lupus syndrome. Symptoms include joint pain, muscle pain, and fever. Hydralazine can also damage the liver. In these cases, the doctor will stop hydralazine treatment. 

Because hydralazine is a niche drug used in a limited number of situations, there are only a few alternatives that may fit a patient’s particular circumstances. Because hydralazine has multiple effects on the circulatory system, hydralazine may be replaced by one or more other drugs that reduce blood pressure, widen blood vessels, or increase the heart’s output. 

What is the maximum dosage for hydralazine?

The maximum daily dose of hydralazine tablets is 300 mg.

Can you overdose on hydralazine?

If too much hydralazine is taken, call a poison control center or get emergency medical care. A hydralazine overdose can cause serious and even life-threatening problems such as low blood pressure, heart rhythm abnormalities, and heart attack. Symptoms of a hydralazine overdose include flushing, fast heartbeat, low blood pressure (hypotension), and headache. 

What interacts with hydralazine?

Hydralazine has some drug interactions, so tell the prescriber about all the prescription drugs, over-the-counter medicines, and supplements being taken, particularly:

  • Certain other blood pressure drugs

  • MAO inhibitors (MAOIs)

  • Drugs called sympathomimetics, such as epinephrine

What happens when you mix hydralazine and alcohol?

Ask the prescriber for medical advice about drinking alcohol while taking hydralazine. Because alcohol reduces blood pressure, healthcare providers generally ask patients to avoid drinking while taking blood pressure-lowering drugs like hydralazine.

Is it safe to take hydralazine during pregnancy?

Healthcare professionals aren’t certain that hydralazine is safe to take while pregnant, but it is a first-line treatment for severe and sudden high blood pressure in pregnant women. In that case, it’s a life-saving treatment for both mother and baby. For other uses, such as heart failure, ask the prescriber for medical advice.

Is it safe to take hydralazine while breastfeeding?

Healthcare professionals are cautious about using hydralazine in women who are breastfeeding. It is present in breast milk, but there is no evidence that it affects lactation or a nursing infant.

What are the side effects of hydralazine?

The most common adverse effects of hydralazine are headache, nausea, vomiting, diarrhea, palpitations, fast heartbeats (tachycardia), and chest pain (angina). Sometimes, hydralazine can cause pain and tingling in the fingers, hands, and feet due to nerve damage (peripheral neuritis). This is not a complete list of side effects. For a comprehensive list, talk to a healthcare provider.

Sources

Medically reviewed by Ashley Wong, Pharm. D.
Licensed Pharmacist

Ashley Wong, Pharm.D., has worked for healthcare companies where she translated complex drug information into easy-to-understand language for patients. She also served as a Senior Medical Information Specialist at a medical communications company, where she delivered clinically accurate drug information to healthcare providers and patients and compiled adverse event reports in accordance with the FDA's reporting guidelines.

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