Hydralazine dosing guide: IV and oral maximums in 24 hours

In this article:

• Hydralazine dosage guide
• Maximum dose of oral hydralazine in 24 hours
• Maximum dose of IV hydralazine in 24 hours
• Factors affecting the maximum dosage of hydralazine
• What to do if you miss a dose of hydralazine
• Hydralazine warnings and precautions

In this article

• Hydralazine dosage guide
• Maximum dose of oral hydralazine in 24 hours
• Maximum dose of IV hydralazine in 24 hours
• Factors affecting the maximum dosage of hydralazine
• What to do if you miss a dose of hydralazine
• Hydralazine warnings and precautions

The Centers for Disease Control and Prevention (CDC) estimates that nearly half of all U.S. adults over age 20 have high blood pressure, which explains why drugs like hydralazine are so important. Hydralazine is a generic prescription medication that’s considered an antihypertensive agent. It is approved by the Food and Drug Administration (FDA) to treat hypertension and may also be prescribed off-label in cases of heart failure. Hydralazine is available in two forms: tablets and injections, each with its own variations in doses. The maximum dose, however, can vary based on the circumstances in which it’s prescribed. 

Hydralazine dosage guide

The dosage for hydralazine largely depends on the condition it’s treating. Here are the standard doses by condition:

• High blood pressure: 10–50 mg tablets taken 4 times daily OR 10–20 mg intravenous injection every 4–6 hours OR 10–50 mg intramuscular injection every 4–6 hours
• High blood pressure emergency: 20–40 mg/dose intravenous or intramuscular injection
• High blood pressure emergency during pregnancy (preeclampsia): 5 mg intravenous or intramuscular injection, then 5–10 mg intravenously every 20–40 minutes
• Heart failure: 25–50 mg tablet taken 3-4 times daily

For emergencies, healthcare providers typically start at the standard dose. But for long-term hypertension treatment, they typically start patients with a lower dose of oral tablets before they titrate up to achieve goal blood pressure parameters. The initial dose is usually 10 mg, four times per day.

Maximum dose of oral hydralazine in 24 hours

The standard dose for oral hydralazine is a range that varies because healthcare providers will tailor the hydralazine treatment to the particular patient and the severity of their hypertension or heart issue. That said, the maximum dose is 300 mg per day. However, according to Genene Salman, Pharm.D., associate professor in the College of Pharmacy at Marshall B. Ketchum University, taking more than 200 mg/day is associated with an increased risk of a lupus-like reaction, such as joint pain, rash, fever, or fatigue. Therefore, healthcare providers are often careful when choosing a dose. 

Maximum dose of IV hydralazine in 24 hours

Like oral hydralazine, IV hydralazine has a range of acceptable doses. When it’s used for preeclampsia, the maximum cumulative dose is 20 mg. However, for other hypertension emergencies, a healthcare provider may administer intramuscular doses of 20–40 mg, but there’s no specified maximum, since it depends on the condition being treated and other factors.

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Factors affecting the maximum dosage of hydralazine

Determining an appropriate dose of hydralazine can be a complicated task, since there are several variables that can influence the maximum amount. As we outlined above, the formulation (oral or intravenous) and the patient’s specific medical condition are significant factors, but others can include:

• Age: Older patients can be more susceptible to low blood pressure (hypotension), so they might require a lower dose or close blood pressure monitoring.
• Liver or kidney disease: Hydralazine is metabolized in the liver and excreted by the kidneys, so issues with either one can slow the drug’s clearance, increasing the concentration in the body.
• Therapeutic response: Healthcare providers need to track how hydralazine is working. For patients in the hospital, they’ll monitor blood pressure regularly and adjust the dose as necessary. In outpatient settings, they may ask the patient to check their blood pressure at home every day using a blood pressure log.
• Side effects: Patients who experience certain adverse effects may need a lower dose. At higher doses, hydralazine can cause hypotension, fluid retention (edema), tachycardia (rapid heartbeat), blood disorders, and lupus-like symptoms. Even more common side effects of hydralazine—like headache, diarrhea, and nausea—can warrant a lower dose if they’re particularly severe.
• Other medications: “Hydralazine is typically prescribed in combination with other antihypertensive medications, which necessitate careful dosage titration and monitoring,” Salman says. “Patients receiving hydralazine should also be on concomitant beta blocker and a diuretic to mitigate reflex tachycardia and fluid accumulation, respectively.” These drugs are commonly prescribed alongside hydralazine, but may require lower doses. For other drug interactions—like monoamine oxidase inhibitors (MAOIs)—healthcare providers typically prescribe hydralazine with caution.
• Heart issues: Healthcare providers may use hydralazine more cautiously in people who have cardiovascular conditions.

Health care providers will consider all these factors before deciding on a specific dosage. Be sure to inform them about any medications you’re taking or preexisting health conditions you have.

What to do if you miss a dose of hydralazine

Missing a dose can be worrisome, but never take a double dose to make up for it. Instead, “If a dose is missed, the patient should take it as soon as they remember unless it’s almost time for the next scheduled dose,” says Michael Genovese, MD, chief medical adviser at AscendantNY. “If it is time for the next dose after a missed dose, do not double up. Skip the missed dose, and continue with your regular schedule.”

Hydralazine warnings and precautions

When healthcare providers determine which hydralazine dosage to prescribe, their goal is to ensure that treatment is effective and safe. Even with diligent dosing and monitoring, there are some things to keep in mind.

Close monitoring

“The manufacturer recommends laboratory tests such as complete blood counts and antinuclear antibody tests prior to and during long-term use of hydralazine. Prescribers should weigh benefits and risks when initiating hydralazine in patients with a positive antinuclear antibody test,” Dr. Salman says. “If new onset blood dyscrasias occur, hydralazine should be stopped.”

This is especially important when hydralazine is administered intravenously or with other medications. Dr. Genovese says this monitoring often includes blood pressure, heart function, and autoimmune symptoms.

Heart disease

“Hydralazine is associated with reflex tachycardia, which can lead to myocardial ischemia (a condition where the heart doesn’t receive enough oxygen). To mitigate this adverse effect, hydralazine should be given concomitantly with a beta blocker,” Dr. Salman says. “Caution should be taken when prescribing hydralazine for severe hypertension, as rapid fluctuations in blood pressure can lead to decreased organ perfusion (e.g., stroke).”

That’s why hydralazine is contraindicated in people with coronary artery disease, a condition characterized by blocked or narrowed arteries. When hydralazine relaxes the blood vessels, it can increase the heart rate, causing the heart to work harder—potentially worsening angina (chest pain) and even possibly leading to heart attacks. It’s also contraindicated in people with damage to the mitral valve from rheumatic fever.

Hypotension and other serious side effects

As mentioned above, in rare cases, hydralazine can cause hypotension—even severe hypotension with rapid IV administration. Additionally, it can cause fluid retention, tachycardia, blood disorders, and lupus-like symptoms. If you experience any of these adverse reactions, contact a healthcare professional right away.

Pregnancy and Breastfeeding

There’s a chance that hydralazine could be harmful to a fetus during pregnancy. Animal studies have shown adverse effects for fetuses, although there hasn’t been as much research into the effects on human pregnancies. Plus, hydralazine has been associated with increased side effects for pregnant mothers.

Research has yet to determine whether hydralazine is excreted in breast milk. However, since many drugs are, it might not be suitable for breastfeeding mothers.

Renal impairment

Because the kidneys excrete hydralazine, decreased kidney function can cause a buildup of the drug in the body. Additionally, some research has found that hydralazine can induce kidney injury and other kidney issues. Therefore, hydralazine should be used with caution in patients with kidney impairment.

Bottom line

Hydralazine is safe when taken as prescribed and is an effective way to treat high blood pressure. The maximum dose of hydralazine in 24 hours depends on various factors, such as whether it’s the oral or IV version and the condition it is being prescribed for. Talk to your healthcare provider if you have questions about how much hydralazine to take in 24 hours and any side effects you’re having.