Hydralazine

Drug Information: Hydralazine

Hydralazine is a direct-acting vasodilator used primarily to treat hypertension. It works by relaxing the smooth muscle of blood vessels, particularly arterioles, leading to a decrease in peripheral resistance and subsequent reduction in blood pressure. Hydralazine is often used in combination with other antihypertensive medications to achieve optimal blood pressure control. Its use extends to managing hypertensive emergencies and gestational hypertension. Careful monitoring is required due to potential side effects such as reflex tachycardia and drug-induced lupus erythematosus.

Category

Antihypertensive

Mechanism of Action

Hydralazine’s primary mechanism of action involves the direct relaxation of arteriolar smooth muscle, leading to vasodilation. The exact mechanism is not fully understood, but it is believed to involve interference with calcium transport within smooth muscle cells, hindering their ability to contract. Specifically, hydralazine is thought to decrease intracellular calcium concentrations in arterial smooth muscle. This reduced calcium influx prevents the interaction of actin and myosin, the contractile proteins, thereby inhibiting vasoconstriction and promoting vasodilation. Unlike some other vasodilators, hydralazine has a greater effect on arterioles than on veins, minimizing the risk of orthostatic hypotension. The vasodilation caused by hydralazine triggers compensatory mechanisms, including increased heart rate (reflex tachycardia), increased cardiac output, and renin release, which can lead to sodium and water retention. Therefore, it’s often prescribed with a beta-blocker to counteract tachycardia and a diuretic to manage fluid retention, optimizing its antihypertensive effect.

Clinical Uses

Hydralazine is primarily used in the management of hypertension. It is effective in treating essential hypertension, often in combination with other antihypertensive drugs such as diuretics and beta-blockers to counteract its compensatory effects. It is also indicated for hypertensive emergencies, especially when rapid blood pressure reduction is needed. Hydralazine is commonly used in the treatment of hypertension during pregnancy (gestational hypertension and pre-eclampsia) due to its relatively well-established safety profile in pregnancy compared to some other antihypertensive agents. Furthermore, Hydralazine, in combination with isosorbide dinitrate, is used to treat heart failure, particularly in African American patients, showing improved survival rates in this population. It’s important to note that while effective, hydralazine’s use requires careful monitoring due to potential side effects and the need to manage associated compensatory mechanisms.

Dosage

Adults:

• Oral: Initially, 10 mg four times daily for 2-4 days, increase to 25 mg four times daily for the remainder of the first week. Increase gradually to a maximum of 50 mg four times daily.
• IV/IM (Hypertensive Emergency): 10-20 mg IV/IM every 4-6 hours as needed. Can also administer as a continuous IV infusion at a rate of 0.2-0.5 mg/kg/hour.

Pediatrics:

• Oral: Initially, 0.75-1 mg/kg/day divided every 6-12 hours, increase gradually to a maximum of 7.5 mg/kg/day or 200 mg/day.
• IV/IM (Hypertensive Emergency): 0.1-0.2 mg/kg IV/IM every 4-6 hours as needed. Maximum single dose: 20 mg.

Note: Dosage adjustments may be required based on individual patient response and renal function.

Indications

Common indications for Hydralazine include:

• Essential Hypertension
• Hypertensive Emergencies
• Gestational Hypertension / Pre-eclampsia
• Heart Failure (in combination with isosorbide dinitrate)

Contraindications

Hydralazine is generally contraindicated in the following situations:

• Hypersensitivity to hydralazine or any of its components
• Coronary artery disease (CAD), especially severe CAD
• Mitral valve rheumatic heart disease
• Severe tachycardia
• Systemic Lupus Erythematosus (SLE)

FAQ

• Q: What is Hydralazine used for?
  
  A: Hydralazine is used to treat high blood pressure (hypertension), including hypertensive emergencies and hypertension during pregnancy. It’s also used in combination with other medications for heart failure.
• Q: How does Hydralazine work?
  
  A: Hydralazine works by relaxing the smooth muscles in the walls of blood vessels, causing them to widen (vasodilation). This reduces the resistance in blood vessels, lowering blood pressure.
• Q: What are the common side effects of Hydralazine?
  
  A: Common side effects include headache, dizziness, fast heart rate (tachycardia), palpitations, nausea, vomiting, and diarrhea.
• Q: Can Hydralazine cause lupus?
  
  A: Yes, in rare cases, Hydralazine can cause drug-induced lupus erythematosus (DILE), especially with high doses or prolonged use.
• Q: Does Hydralazine interact with other medications?
  
  A: Yes, Hydralazine can interact with other antihypertensive drugs, potentially leading to excessive blood pressure lowering. It can also interact with MAO inhibitors and certain NSAIDs. Always inform your doctor about all medications you are taking.
• Q: Is Hydralazine safe to use during pregnancy?
  
  A: Hydralazine is considered relatively safe for use during pregnancy to treat hypertension, but it should only be used under the guidance of a healthcare professional.
• 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 close to the 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: How long does it take for Hydralazine to start working?
  
  A: The onset of action is relatively rapid, with effects typically seen within 20-30 minutes after IV administration and within 1-2 hours after oral administration.