iCliniq logo

Ask a Doctor Online Now

HomeHealth articleshypertensionWhat Is Hydralazine?

Hydralazine - Uses, Side Effects, Dosage, Precautions, and Interactions

Verified dataVerified data

4 min read


Hydralazine is used as a hypertensive drug to treat severe, essential hypertension. Read below its uses, dosage, side effects, precautions, and more.

Medically reviewed by

Dr. Prashant Valecha

Published At December 27, 2022
Reviewed AtFebruary 1, 2023

What Is Hydralazine?

Hydralazine dilates the blood vessels and is used to treat essential hypertension. The drug may be used intravenously to reduce blood pressure in hypertensive urgency or emergency rapidly. The hydralazine-oral tablet is available only as a generic drug with a doctor's prescription.

Why Is Hydralazine Prescribed?

Hydralazine is primarily used to manage hypertension. Controlled blood pressure can help prevent strokes, heart attacks, kidney failure, and other heart problems. The antihypertensive may be used to treat hypertensive crises and as an adjunct therapy for heart failure. Hydralazine is also used as first-line therapy to control high blood pressure in pre-eclampsia or other emergencies during pregnancy. Intravenous Hydralazine may be given in hypertensive emergencies to hospitalized patients. When combined with Propranolol, Hydralazine improves blood pressure and reduces each drug's side effects.

How Does Hydralazine Work?

Hydralazine is a peripheral arterial vasodilator that relaxes blood vessels carrying blood toward the organs and tissues and away from the heart. It inhibits the inositol triphosphate-induced calcium release from the smooth muscle cells and myosin phosphorylation within the arterial smooth muscle. This reduces peripheral vascular resistance release of epinephrine and norepinephrine. This helps to increase venous return and cardiac output. Hydralazine is often given with beta-blockers or diuretics for better patient tolerance.

Hydralazine undergoes polymorphic acetylation when given in low doses and is primarily metabolized in the liver. The acetylated and unchanged drugs are excreted in the urine and feces. When given orally, Hydralazine lowers the blood pressure usually within an hour and stays in the body for three to seven hours. Taking Hydralazine with food improves the bioavailability of the drug. The intravenous administration of Hydralazine lowers the blood pressure within 5 to 30 minutes of dosing.

How to Take Hydralazine?

Hydralazine is available as a tablet to be taken by mouth, usually three to four times a day. Taking Hydralazine on an empty stomach or one to two hours after meals is best. Take medicine at the same time of the day or at regular intervals, and it should not be stopped suddenly. It is required to monitor blood pressure regularly while taking Hydralazine. Hydralazine must be kept in a cool, dry place and away from direct heat and sunlight. Hydralazine must be stored out of reach of children and pets.

What Is the Dosage of Hydralazine?

The dose and the frequency may vary depending on the age, the condition being treated, the severity of the condition, other medical conditions, and the reaction to the first dose. The treatment may be started at a low dose and increased gradually.

The recommended dose is 10 mg orally four times a day for the first 2 to 4 days, with a maximum daily dose of 300 mg.

Hydralazine oral dosage

What Are the Side Effects of Using Hydralazine?

Hydralazine oral tablets usually do not cause drowsiness but may cause side effects such as

  • Headaches.

  • Loss of appetite.

  • Nausea.

  • Vomiting.

  • Diarrhea.

  • Fast heart rate.

  • Chest pain.

  • Weakness.

  • Flushing.

Hydralazine can cause serious side effects like

  • Very low blood pressure.

  • Dizziness.

  • Fast heart rate.

  • Swelling in the arms and legs.

  • Numbness or tingling.

  • Itching.

  • Change in appetite.

  • Fever.

  • Chills.

  • Pain in the joints.

  • Trouble breathing.

  • Devere constipation.

  • Trouble in passing urine.

What Are the Precautions and Warnings of Hydralazine?

  • Allergies - Hydralazine can cause severe allergic reactions with symptoms like trouble breathing, swelling of the throat and tongue, and hives. The drug should not be taken if you have ever had an allergic reaction to Hydralazine.

  • Pregnancy and Breastfeeding - Hydralazine is a category C pregnancy drug and can cause adverse effects on the fetus. The drug passes into the human breastmilk.

  • Elderly - Hydralazine is not recommended in elderly patients because of the increased risk of adverse effects and unpredictable antihypertensive effects.

  • Children - Hydralazine should not be given to children below six.

  • Mental Alertness - Hydralazine may cause dizziness and drowsiness and should not be taken while driving or using machinery.

  • Kidney Damage - Therapy with Hydralazine should be administered with caution in patients with advanced kidney damage, as it may worsen the condition.

  • Alcohol - Drinking alcohol with Hydralazine can increase the risk of arrhythmias, falls, and severe drowsiness and should be avoided.

What Are the Interactions of Hydralazine?

It is important to manage all your medications as Hydralazine can interact with other medications, herbs, or vitamins.

Interaction with Drugs:

Examples of medications that may interact with Hydralazine include

  • Monoamine oxidase inhibitors (MAOIs) such as Isocarboxazid, Phenelzine sulfate,

  • Tranylcypromine sulfate and Selegiline.

  • Thiazides such as Diazoxide.

  • Dobutamine.

  • Dopamine.

  • Norepinephrine.

  • Metaraminol.

  • Methoxamine.

  • Phenylephrine.

  • Phenylpropanolamine.

  • Ephedra.

Food Interaction:

Eat or drink potassium-rich foods like oranges or other citrus fruit juices. The use of Hydralazine may cause loss of potassium from the body.

Interaction with Disease:

  • Bone Marrow Suppression - Hydralazine may cause some patients' blood dyscrasias, such as reduced hemoglobin, leukopenia, and purpura. Hydralazine therapy should be cautiously administered in patients with bone marrow suppression conditions and must be discontinued if abnormalities occur.

  • Coronary Artery Disease - Hydralazine is contraindicated in patients with coronary artery disease, as there may be episodes of reflex tachycardia, palpitations, and chest pain.

  • Lupus Erythematosus - Hydralazine therapy should not be given to people with preexisting lupus erythematosus as there can be an exacerbation of the disease. When taken long-term, it is important to monitor complete blood counts and antinuclear antibody titers.

  • Valvular Heart Disease - Hydralazine is contraindicated in patients with mitral valvular rheumatic heart disease. An increased rate of palpitations may provoke angina or myocardial infarction.

  • Renal Dysfunction - Hydralazine should be cautiously administered in patients with advanced renal damage as they may develop glomerulonephritis. Low doses of Hydralazine may be given with renal function monitoring.

  • Cerebral Vasculopathy - Therapy with Hydralazine may aggravate cerebral vasculopathy and should be given with caution.


Hypertension often has no symptoms but, if left untreated, can cause damage to the brain, heart, blood vessels, kidneys, and other body parts. This can increase the risk of heart attacks, stroke, kidney failure, vision loss, and other problems. Along with medications, it is recommended to make lifestyle changes, including eating a low-fat diet, maintaining weight, exercising, and avoiding smoking and alcohol. This can help to further lower your blood pressure.

Frequently Asked Questions


What Is the Action of Hydralazine?

Hydralazine is a direct vasodilator, whereas vasodilator means the relaxation of the smooth muscles in the blood vessels. It is prescribed for the treatment of high blood pressure. It works by relaxing the mechanism of the blood vessels. In addition, it increases the oxygen and blood supply to the heart, thereby decreasing the workload.


How Will Hydralazine Clear From the System?

The average half-life of Hydralazine is about 2.2 to 7.8 hours in the case of rapid acetylators and 2.0 to 5.8 hours in the slow form of acetylators. Hydralazine is recovered at less than ten percent in feces and sixty-five to ninety percent in urine.


What Is the Daily Recommended Dose of Hydralazine?

Hydralazine is used to treat high forms of blood pressure. The recommended initial dose is 0.75 mg/kg/day, which can be divided into four dosages. The doctors gradually increase the dosage to a maximum dose of 7.5 mg/kg/day or 200 mg/day and never more than this.


How Long Will Hydralazine Take to Act?

Hydralazine shows blood pressure lowering effects in about 20 to 30 minutes with oral administration, five to 20 minutes with intravenous administration, and ten to 30 minutes with intramuscular administration. Nevertheless, the effects last for quite a few hours, and thus multiple doses are given in a day.


How Does Hydralazine Help Relax Blood Vessels?

Hydralazine is a vasodilator which means it relaxes the blood vessels to lower the blood pressure in the system. So, it relaxes the blood vessels by means of widening the blood vessels and permitting free flow of blood and oxygen. This process eventually reduces the force of the heart that needs to exert the blood. As a result, blood pressure is lowered.


How Long Can Hydralazine Be Taken?

The duration and frequency of Hydralazine depend upon the individual’s medical condition and the severity of hypertension. However, the Hydralazine tablets are prescribed in tearing dosages to be taken four times a day.


How Far Is Hydralazine Available on the Market?

Hydralazine is a prescribed medication used in the treatment of heightened blood pressure and heart failure. The medication Hydralazine is still an option for several years, though a range of antihypertensive medications is available in the market.


How Often Is Hydralazine Given?

Hydralazine stays in the system for only a few hours, so it is usually given two to four times a day. The doctors give an initial dose of 10 mg four times a day. Then the dosage is increased to 50 mg on a gradual basis and not more than that. So it is taken about four times in a day, so one should take the medication at a similar time every day.


How to Take Hydralazine?

Hydralazine is available in many forms, such as tablets and solutions for intravenous and intramuscular injections. The injections are given in hospital settings by medical healthcare professionals. Tablets are advised to ingest with or without food for about two to four times in a day.


What Is the Use of Hydralazine Pills?

Hydralazine is used to treat high forms of blood pressure primarily. It is also prescribed in the following states.
 - Control heightened blood pressure in women during times of pregnancy.
 - Control extremely high degrees of blood pressure in an emergency crisis. 


How Much Isosorbide Dinitrate and Hydralazine Be Taken?

The combination of Hydralazine and Isosorbide dinitrate is prescribed for the management of high blood pressure and several heart concerns. One tablet constitutes 37.5 mg of Hydralazine and 20 mg of Isosorbide dinitrate which can be given three times a day.


What Are the Effects of Hydralazine on Kidneys?

Hydralazine should be monitored and considered conscientiously since it can lead to unfavorable and adverse events. This includes severe forms of acute kidney injury that can progress into chronic kidney disease and even death.


How About the Absorption of Hydralazine?

Hydralazine is a direct form of vasodilator used for high blood pressure states. Clinical findings of the pharmacokinetic report show that Hydralazine is well absorbed from the gastrointestinal tract. It includes a complex and extensive metabolism process.


What Is the Effect of Hydralazine on Heartbeat?

Hydralazine works effectively in alleviating the symptoms. But, it is evident that Hydralazine showed a twenty percent or increased effect on heart rate. The blood pressure is lowered in the case of hypertensive individuals but with lesser side effects.


How Can Hydralazine Be Administered?

Hydralazine is a vasodilator that relaxes the blood streams and diminishes the blood pressure in individuals with high ranges. It is administered orally in the management of hypertension and administered intravenously to rightly decrease blood pressure in hypertensive emergency cases.
Source Article IclonSourcesSource Article Arrow
Dr. Prashant Valecha
Dr. Prashant Valecha



Community Banner Mobile
By subscribing, I agree to iCliniq's Terms & Privacy Policy.

Source Article ArrowMost popular articles

Ask your health query to a doctor online


*guaranteed answer within 4 hours

Disclaimer: No content published on this website is intended to be a substitute for professional medical diagnosis, advice or treatment by a trained physician. Seek advice from your physician or other qualified healthcare providers with questions you may have regarding your symptoms and medical condition for a complete medical diagnosis. Do not delay or disregard seeking professional medical advice because of something you have read on this website. Read our Editorial Process to know how we create content for health articles and queries.

This website uses cookies to ensure you get the best experience on our website. iCliniq privacy policy