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

Published on Dec 27, 2022 and last reviewed on Feb 01, 2023   -  5 min read


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

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

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.

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Last reviewed at:
01 Feb 2023  -  5 min read




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