What are the available formulations and dosing increments of hydralazine (direct vasodilator)?

Available Formulations and Dosing Increments of Hydralazine

Hydralazine is available in oral tablets of 10 mg, 25 mg, 50 mg, and 100 mg, and as an injectable formulation of 20 mg/mL for intravenous administration. 1, 2, 3

Oral Hydralazine Formulations

Standard Tablets

• 10 mg tablets
• 25 mg tablets
• 50 mg tablets
• 100 mg tablets

Dosing Considerations for Oral Administration

• Initial dosing: 25-50 mg 3-4 times daily 1
• Maximum daily dose: 300 mg in divided doses 1
• Fixed-dose combination with isosorbide dinitrate:
  • Initial: 37.5 mg hydralazine/20 mg isosorbide dinitrate 3 times daily
  • Target: 75 mg hydralazine/40 mg isosorbide dinitrate 3 times daily 1

Special Population Considerations

• Pediatric dosing: Initial 0.75 mg/kg daily in four divided doses, may increase gradually over 3-4 weeks to maximum 7.5 mg/kg or 200 mg daily 3
• Renal impairment: Lower doses may be required, especially in patients with marked renal damage 2
• Acetylator status: Slow acetylators may require lower doses due to decreased metabolism of the drug 4

Injectable Hydralazine Formulation

• Concentration: 20 mg/mL solution for injection 2
• Initial IV dosing: 10-20 mg via slow IV infusion 5, 2
• Hypertensive emergency dosing: Initial 10 mg via slow IV infusion, repeated every 4-6 hours as needed 1, 5
• Maximum IV dose: 40 mg per administration 2

Dosing Frequency Considerations

• Oral administration:

  • For heart failure: 3-4 times daily dosing is recommended 1
  • For hypertension: Twice daily dosing is generally sufficient due to the pharmacokinetic profile 6

• IV administration:

  • Effects begin within minutes
  • Peak effect: 10-80 minutes
  • Duration: 2-4 hours, with effects potentially lasting up to 12 hours 5, 2

Clinical Pearls and Caveats

• The unpredictability of response and prolonged duration of action make hydralazine less desirable as a first-line agent for acute hypertension treatment 1, 5
• IV hydralazine may discolor upon contact with metal; discolored solutions should be discarded 2
• Patients with renal impairment (CCr <35 ml/min) have a significantly longer duration of action (14.3 ± 1.4 hours vs 7.9 ± 0.5 hours) and may require less frequent dosing 7
• Acetylation of hydralazine is a capacity-limited process, meaning higher doses may result in disproportionately higher blood levels, particularly in slow acetylators 4

Hydralazine's availability in multiple dosage forms and strengths allows for flexible dosing strategies to optimize blood pressure control while minimizing adverse effects such as reflex tachycardia and headache.