Hydralazine

Drug Information: Hydralazine

Hydralazine is a direct-acting vasodilator, primarily used to lower blood pressure. It exerts its effect by relaxing the smooth muscle in arterial blood vessels, leading to a decrease in peripheral resistance. It is available in both oral and intravenous formulations. While effective, it is often used in combination with other antihypertensive agents due to its potential for reflex tachycardia and sodium retention. Hydralazine is also used, albeit less frequently now, in the treatment of heart failure in combination with isosorbide dinitrate, particularly in African American patients.

Category

Vasodilator (including nitrates)

Mechanism of Action

Hydralazine’s mechanism of action primarily involves the direct relaxation of arteriolar smooth muscle. While the precise molecular mechanism remains incompletely understood, it’s thought to interfere with calcium movement within the smooth muscle cells. This reduced intracellular calcium concentration hinders the interaction of actin and myosin, which are crucial for muscle contraction. Unlike some other vasodilators, hydralazine primarily affects arteries, with minimal impact on veins. This selective arterial vasodilation reduces systemic vascular resistance, leading to a decrease in blood pressure. The reduction in blood pressure triggers compensatory mechanisms, including increased heart rate, cardiac output (reflex tachycardia), and sodium and fluid retention mediated by the renin-angiotensin-aldosterone system (RAAS). These compensatory responses often necessitate the co-administration of beta-blockers to control heart rate and diuretics to manage fluid retention when using hydralazine for chronic hypertension.

Clinical Uses

Hydralazine is primarily utilized in the management of hypertension. It can be used as part of a multi-drug regimen for chronic hypertension or in hypertensive emergencies, particularly when rapid blood pressure reduction is required intravenously. It is also used to treat pre-eclampsia and eclampsia during pregnancy. Furthermore, hydralazine has a role in the treatment of heart failure. In combination with isosorbide dinitrate, it has been shown to improve survival and reduce hospitalizations in patients with heart failure, especially in self-identified African American patients. This combination is particularly effective in patients who cannot tolerate ACE inhibitors or ARBs. Hydralazine is sometimes used as an adjunctive treatment in patients with resistant hypertension, who are already taking multiple other antihypertensive medications.

Dosage

Adults:

• Hypertension:
  • Oral: Initially 10 mg four times daily for 2-4 days, increase to 25 mg four times daily for the rest of the first week. Adjust dosage to the lowest effective level for maintenance; usually 50 mg to 200 mg daily in divided doses. In some patients, up to 300 mg/day may be required.
  • IV: 10-20 mg IV every 4-6 hours as needed. In hypertensive emergencies, the dose can be titrated more rapidly.
• Heart Failure: Typically used in combination with isosorbide dinitrate. Dosage is determined on an individual basis.

Pediatrics:

• Hypertension:
  • Oral: Initial: 0.75-1 mg/kg/day in 2-4 divided doses; Max: 25 mg/dose. Increase gradually over 3-4 weeks to a maximum of 7.5 mg/kg/day or 200 mg/day.
  • IV: 0.1-0.2 mg/kg/dose IV every 4-6 hours as needed.

Indications

Common indications for Hydralazine include:

• Essential hypertension
• Hypertensive emergencies
• Management of pre-eclampsia and eclampsia
• Heart failure (in combination with isosorbide dinitrate)
• Resistant hypertension

Contraindications

Hydralazine is contraindicated in the following conditions:

• Hypersensitivity to hydralazine
• Coronary artery disease
• Mitral valve rheumatic heart disease
• Severe tachycardia
• Systemic lupus erythematosus (SLE) or SLE-like syndrome
• Severe hypotension

FAQ

Q: How does Hydralazine work to lower blood pressure?
A: Hydralazine directly relaxes the smooth muscle in arterial blood vessels, leading to vasodilation and a decrease in peripheral resistance. This results in a lower blood pressure.

Q: What are the common side effects of Hydralazine?
A: Common side effects include headache, flushing, palpitations, tachycardia, nausea, vomiting, and dizziness. More serious side effects can include drug-induced lupus-like syndrome and severe hypotension.

Q: Can Hydralazine be used during pregnancy?
A: Yes, Hydralazine can be used in pregnancy for the management of hypertension, including pre-eclampsia and eclampsia. However, it should be used under close medical supervision.

Q: Why is Hydralazine often prescribed with other medications?
A: Hydralazine can cause reflex tachycardia and sodium/fluid retention. Therefore, it’s often prescribed with a beta-blocker to control heart rate and a diuretic to manage fluid balance.

Q: What is drug-induced lupus syndrome?
A: Drug-induced lupus syndrome is a condition where the body produces antibodies against its own tissues, mimicking the symptoms of lupus. Hydralazine is a known trigger for this condition, especially with high doses and prolonged use.

Q: How often should I take Hydralazine?
A: Hydralazine is typically taken multiple times a day. The exact frequency and dosage will be determined by your doctor based on your individual needs and response to the medication.

Q: What should I do if I miss a dose of Hydralazine?
A: If you miss a dose, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not double the dose to catch up.

Q: Are there any foods or drinks I should avoid while taking Hydralazine?
A: You should avoid excessive salt intake, as this can counteract the effects of Hydralazine. Consult with your doctor or pharmacist about specific dietary recommendations.