What is the recommended oral dose of hydralazine (direct vasodilator) for managing severe hypertension?

Recommended Oral Dose of Hydralazine for Severe Hypertension

For severe hypertension, the recommended initial oral dose of hydralazine is 10 mg four times daily for the first 2-4 days, then increased to 25 mg four times daily for the remainder of the first week, followed by 50 mg four times daily for maintenance therapy. 1

Dosing Algorithm for Oral Hydralazine

Initial Dosing Phase

• First 2-4 days: 10 mg four times daily
• Remainder of first week: 25 mg four times daily
• Second week and beyond: 50 mg four times daily

Dose Titration

• Adjust dosage to the lowest effective level for maintenance therapy
• For resistant hypertension, doses may be increased up to 300 mg daily (75 mg four times daily), though this higher dose increases risk of adverse effects 1
• When higher doses are required, consider combining hydralazine with a thiazide diuretic and/or beta-blocker to allow for lower hydralazine doses

Special Considerations

Resistant Hypertension Management

In patients with resistant hypertension, hydralazine is typically added at Step 5 of therapy after optimizing other antihypertensive medications:

• Start with 25 mg three times daily
• Titrate upward to maximum dose as needed 2

Heart Failure Patients

For patients with heart failure and hypertension, hydralazine is often used in combination with isosorbide dinitrate:

• Initial dose: 25-50 mg hydralazine three to four times daily
• Target dose: Up to 75 mg three times daily or 300 mg total daily in divided doses 2

Efficacy and Monitoring

• IV hydralazine produces more rapid and significant blood pressure reduction compared to oral formulations (13-18 mmHg reduction in mean arterial pressure within 6 hours) 3
• Oral hydralazine shows a moderate effect (approximately 6 mmHg reduction in mean arterial pressure) 3
• Blood pressure begins to decrease within 10-30 minutes of administration, with effects lasting 2-4 hours 2
• Regular monitoring is essential due to the unpredictability of response

Important Caveats

• Hydralazine is not a first-line agent for most hypertensive emergencies due to its unpredictable response and prolonged duration of action 2
• The drug should be initiated at lower doses and gradually increased to minimize adverse effects
• Slow acetylators may require lower doses due to increased sensitivity to the drug's effects 4
• Patients should be monitored for development of lupus-like syndrome, especially at higher doses
• Food increases plasma levels of hydralazine, so consistent administration with respect to meals is important 1

Contraindications and Precautions

• Use caution in patients with coronary artery disease as reflex tachycardia may worsen angina
• Monitor for fluid retention, which may require adjustment of diuretic therapy
• Be aware of potential drug interactions, particularly with other antihypertensives

By following this structured approach to hydralazine dosing for severe hypertension, clinicians can maximize efficacy while minimizing adverse effects.