What is the initial dose of hydralazine (direct vasodilator) for hypertension?

Initial Dose of Hydralazine for Hypertension

The initial dose of hydralazine for hypertension 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. 1

Intravenous (IV) Hydralazine for Hypertensive Emergencies

• For hypertensive emergencies requiring IV administration, the initial dose is 10 mg via slow IV infusion (maximum initial dose 20 mg), which can be repeated every 4-6 hours as needed 2
• Blood pressure begins to decrease within 10-30 minutes after IV administration, and the effect lasts 2-4 hours 2
• Due to unpredictability of response and prolonged duration of action, hydralazine is not considered a desirable first-line agent for acute treatment in most hypertensive emergency patients 2

Oral Hydralazine for Chronic Hypertension Management

Dosing Schedule and Titration

• Initial oral dosing: 10 mg four times daily for first 2-4 days 1
• Week 1: Increase to 25 mg four times daily 1
• Week 2 and beyond: Increase to 50 mg four times daily 1
• Maintenance: Adjust to lowest effective dose 1
• For resistant hypertension: Up to 300 mg daily may be required, though combining with other antihypertensives at lower hydralazine doses is preferred 1

Important Considerations for Dosing

• Acetylator status affects dosing requirements:

  • Slow acetylators achieve therapeutic effects at lower doses 3
  • Fast acetylators may require higher doses to achieve the same effect (D50 is 1.68 mg/kg for fast acetylators vs. 0.87 mg/kg for slow acetylators) 3
  • Slow acetylators are more prone to side effects 4

• Combination therapy considerations:

  • Hydralazine is often used with a beta-blocker and/or diuretic 1, 5
  • Beta-blockers help counteract the reflex tachycardia caused by hydralazine 6
  • Individual titration is essential to ensure the lowest possible therapeutic dose of each drug 1

Formulations and Dosing Frequency

• Immediate-release tablets: Traditional dosing is 2-4 times daily 5, 6
• Extended-release formulations: May allow for once or twice daily dosing 5, 7
• Once-daily conventional hydralazine may be insufficient as its hypotensive effect wanes at 24 hours, particularly in rapid acetylators 5

Monitoring and Safety

• The incidence of toxic reactions, particularly lupus-like syndrome, is higher in patients receiving large doses of hydralazine 1
• Blood pressure response should be monitored to determine effectiveness and guide dose adjustments 3
• Combination with beta-blockers provides additional blood pressure reduction (approximately 6.6 mmHg) beyond hydralazine effect 3

Special Considerations

• For heart failure patients, hydralazine is often used in combination with isosorbide dinitrate, with an initial dose of 25-50 mg hydralazine three or four times daily 2
• In resistant cases, consider acetylator status when determining optimal dosing strategy 3, 4