hydralazine

Hydralazine (Apresoline) is an antihypertensive medication used to treat essential hypertension (high blood pressure), alone or in-combination with other anti-hypertensive medications. It is also used for treating hypertensive crisis and congestive heart failure. It is a peripheral arterial vasodilator and causes relaxation of blood vessels which carry blood away from the heart and towards the organs and tissues.

The exact mechanism of how hydralazine causes arterial smooth muscle relaxation is not yet understood. Hydrazine affects calcium movement within blood vessels. Calcium is required for muscle contraction and therefore disturbances in calcium movement may cause smooth muscle relaxation in the blood vessels. Hydralazine is selective for arterioles (small arteries), and the overall effects of treatment include a decrease in arterial blood pressure, and peripheral vascular resistance.

In addition to treating high blood pressure, hydralazine has shown to be beneficial for the treatment of congestive heart failure (CHF). Although ACE inhibitors are preferred for the treatment of CHF, hydralazine in combination with isosorbide dinitrate (Isordil, Isordil Titradose, Dilatrate-SR) is an alternative for patients who cannot tolerate ACE inhibitors.

Hydralazine was approved by the US Food and Drug Administration (FDA) in 1952 as an antihypertensive agent. It is commonly used for the treatment of hypertension in pregnancy. Parenteral or injectable hydralazine is used to treat hypertensive emergencies (severally high blood pressure) during pregnancy.

Common side effects of hydralazine are:

• headache,
• anorexia,
• nausea,
• vomiting,
• diarrhea,
• palpitations,
• tachycardia (rapid heartbeat), and
• angina pectoris (chest pain).

Other less commonly reported side effects include:

• constipation,
• paralytic ileus,
• low blood pressure,
• edema,
• paradoxical pressor response,
• dyspnea (shortness of breath),
• peripheral neuritis,
• numbness,
• tingling,
• tremors,
• muscle cramps,
• psychotic reactions,
• difficulty urinating,
• blood disorders,
• hypersensitivity type reactions,
• nasal congestion,
• flushing,
• abnormal tear production (lacrimation) , and
• conjunctivitis.

Hypertension in adult patients:

• Start treatment at a low dose and increase gradually based on individual patient response. The usual recommended starting regimen is 10 mg orally four times daily for the first 2 to 4 days, increase to 25 mg four times daily for the remainder of the first week.
• For the second and subsequent weeks, increase dosage to 50 mg four times daily (increase dose by 10-25 mg/dose gradually every 2-5 days).
• The maximum daily dose used in clinical studies is 300 mg.

Congestive heart failure:

• The initial dose for treating heart failure is 10 to 25 mg orally 3 to 4 times daily.
• The usual dose is 225 to 300 mg daily in 3 to 4 divided doses.

For pediatric hypertensive emergencies, the dose is 0.5 mg/Kg IV every 4 hours.

Sympathomimetics such as:

• cocaine,
• dobutamine (Dobutrex),
• dopamine (Intropin),
• norepinephrine (Levophed),
• epinephrine (Adrenalin),
• metaraminol (Aramine),
• methoxamine,
• phenylephrine, (NeoSynephrine, Neofrin)
• phenylpropanolamine,
• ephedra (Ma Huang), and
• ephedrine may decrease the effectiveness of hydralazine.

Co-administration of these agents may block the anti-hypertensive benefits of hydralazine treatment.

Hydralazine should be used in pregnancy only if the potential benefit justifies the potential risk to the fetus. Hydralazine is classified as FDA pregnancy risk category C (Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks). It is used for treating high blood pressure during pregnancy.

Hydralazine is excreted in breast milk. Hydralazine should be used cautiously in females who are breastfeeding if treatment is necessary.

What preparations of hydralazine-oral are available?

Tablets: 10, 25, 50, 100 mg; Solution for injection: 20 mg/ml

How should I keep hydralazine-oral stored?

Tablets and injection solution may be stored at room temperature between 20 C to 25 C (68 F to 77 F).