Hydralazine – Dose & Side Effects


Originally developed in the 1950s as a malaria treatment, hydralazine showed antihypertensive ability and was soon repurposed. Hydralazine is a hydrazine derivative vasodilator used alone or as adjunct therapy in the treatment of hypertension and only as adjunct therapy in the treatment of heart failure. Hydralazine is no longer a first line therapy for these indications since the development of newer antihypertensive medications.

Hydralazine hydrochloride was FDA approved on 15 January 1953.

Properties and Characteristics of Hydralazine

Drug class Vasodilators
Brand Names  Apresoline, Bidil
Synonyms 1-Hydrazinophthalazine, 1-Phthalazinylhydrazine, 6-Hydralazine, Hidralazina, Hydralazin, Hydralazine, Hydralazinum, Hydrallazine, Hydrazinophthalazine, Hypophthalin, Idralazina
Molecular Formula      C8H8N4
Molecular Weight 196.64 g/mol
IUPAC Names phthalazin-1-ylhydrazine;hydrochloride
Structural formula of main component
Pure active ingredient Hydralazine Hydrochloride
Appearance    White, crystalline powder
Melting Point 273 °C
Solubility In water, 44.2 g/l @ 25 °C;
Available as Tablet, Solution, Powder, Injection
Storage Store at a temperature less than 40 °C
Prescription Prescription is required

What is Hydralazine (Apresoline) used for?

  • Hypertension
  • Hypertensive Emergency
  • Pre-eclampsia/Eclampsia
  • Cardiovascular Disease
  • Hypertensive Congestive Heart Failure
  • Hypertensive Heart (w/ CHF) and renal disease
  • Hypertensive Heart (w/o CHF) and renal disease
  • Hypertensive Renal Disease
  • Hypertensive Retinopathy
  • Renovascular Hypertension
  • Hypertensive Encephalopathy
  • Hypertensive Heart Disease

Hydralazine side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Hydralazine may cause serious side effects. Call your doctor at once if you have:

  • Chest pain or pressure, pain spreading to your jaw or shoulder;
  • Fast or pounding heartbeats;
  • A light-headed feeling, like you might pass out;
  • Numbness, tingling, or burning pain in your hands or feet;
  • Painful or difficult urination;
  • Little or no urination; or
  • Lupus-like syndrome–joint pain or swelling with fever, swollen glands, muscle aches, chest pain, vomiting, unusual thoughts or behavior, and patchy skin color.

Common side effects of hydralazine may include:

  • Chest pain, fast heart rate;
  • Headache; or
  • Nausea, vomiting, diarrhea, loss of appetite.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Mechanism of action

Hydralazine may interfere with calcium transport in vascular smooth muscle by an unknown mechanism to relax arteriolar smooth muscle and lower blood pressure. The interference with calcium transport may be by preventing influx of calcium into cells, preventing calcium release from intracellular compartments, directly acting on actin and myosin, or a combination of these actions. This decrease in vascular resistance leads to increased heart rate, stroke volume, and cardiac output.

Hydralazine also competes with protocollagen prolyl hydroxylase (CPH) for free iron. This competition inhibits CPH mediated hydroxylation of HIF-1α, preventing the degradation of HIF-1α. Induction of HIF-1α and VEGF promote proliferation of endothelial cells and angiogenesis.

Drug Interactions with Hydralazine

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • Enteral Nutrition

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Angina (severe chest pain) or
  • Blood disease or
  • Heart attack, history of or
  • Heart rhythm problems or
  • Hypotension (low blood pressure) or
  • Peripheral neuritis (nerve problem) or
  • Stroke, history of or
  • Systemic lupus erythematosus—Use with caution. May make these conditions worse.
  • Coronary artery disease or
  • Mitral valvular rheumatic heart disease—Should not be used in patients with these conditions.
  • Kidney disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.
  • Phenylketonuria—The oral solution contains aspartame, which can make this condition worse.

Dosing of Hydralazine

The dose of this medicine will be different for different patients. Follow your doctor’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For high blood pressure

For oral dosage form (oral solution):

Adults—40 to 200 milligrams (mg) per day, divided into two or four doses.

Children—Dose is based on body weight and must be determined by your doctor. The dose is usually 0.75 to 7.5 milligram (mg) per kilogram (kg) of body weight per day, divided into two or four doses.

For oral dosage form (tablets):

Adults—At first, 10 milligrams (mg) four times a day. Your doctor may adjust your dose as needed. However, the dose is usually not more than 50 mg four times a day.

Children—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 0.75 milligram (mg) per kilogram (kg) of body weight per day, divided into four doses. The doctor may adjust the dose as needed. However, the dose is usually not more than 7.5 mg per kg of body weight per day or 200 mg per day.



The signs and symptoms of hydralazine overdose include hypotension, tachycardia, headache and generalised skin flushing. Complications can include myocardial ischemia and subsequent myocardial infarction, cardiac arrhythmias, profound shock and coma.


There is no specific antidote. Gastric lavage should be instituted as soon as possible, taking adequate precautions against aspiration and for protection of the airway. An activated charcoal slurry may be instilled if conditions permit. These procedures may have to be omitted or carried out after cardiovascular status has been stabilised since they might precipitate cardiac arrhythmias or increase the depth of shock.

Support of the cardiovascular system is of primary importance. Shock should be treated with plasma expanders, if possible, rather than vasopressors. Supportive measures including intravenous fluids are also indicated. If hypotension is present, an attempt should be made to raise the blood pressure without increasing the tachycardia. If a vasopressor is used, one should be chosen that is least likely to precipitate or aggravate cardiac arrhythmia. Tachycardia responds to beta-blockers. Digitalisation may be necessary. Fluid and electrolyte status and renal function should be monitored.

Hydralazine warnings

This drug comes with several warnings.


Hydralazine can cause a severe allergic reaction. Symptoms can 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 before. Taking it again could be fatal (cause death).

Alcohol interaction

The use of drinks that contain alcohol can increase the blood pressure-lowering side effects from hydralazine. If you drink alcohol, talk to your doctor.

Warnings for certain groups

For people with heart problems: Use this drug with caution if you have heart problems. Hydralazine may cause a heart attack, especially if you already have heart issues. Be sure to tell your doctor about your heart condition before taking hydralazine.

For pregnant women: Hydralazine 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. Hydralazine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

For women who are breastfeeding: Small amounts of hydralazine may pass into breast milk. However, this drug doesn’t typically cause side effects in a child who is breastfed. If you breastfeed your baby, talk to your doctor about the safety of this drug.

For seniors: Older adults may process drugs more slowly. A normal adult dose may cause levels of this drug to be higher than normal in your body. If you’re a senior, you may need a lower dose or a different schedule.

For children: This drug hasn’t been studied in children younger than 18 years, but it has been used in children.

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