How to administer hydralazine for severe hypertension?

Hydralazine Administration for Severe Hypertension

Do not use hydralazine as a continuous infusion—administer only as intermittent IV bolus doses, starting with 5 mg IV given slowly over 5 minutes, repeated every 20-30 minutes as needed (maximum 25 mg per episode), with blood pressure monitoring every 5-10 minutes until stable. 1, 2, 3

Critical Administration Protocol

Initial Dosing

• Start with 5 mg IV bolus given slowly over 5 minutes 2
• Repeat doses of 10 mg IV every 20-30 minutes if blood pressure remains elevated 1, 2
• Maximum cumulative dose is 25 mg per treatment episode 2
• The FDA label indicates 20-40 mg as the usual dose range, but obstetrical guidelines favor the more conservative 5-10 mg approach 3, 1

Why Bolus Only, Never Continuous Infusion

• Continuous hydralazine infusion causes rapid, uncontrolled blood pressure decline and resulted in fetal distress requiring cesarean delivery in 5 of 7 patients in one study 4
• Bolus dosing is significantly more effective, achieving blood pressure control in 65 minutes versus 186 minutes with continuous drip 5
• Bolus dosing requires lower total doses (6.68 mg vs 20.07 mg) without causing overshoot hypotension 5

Monitoring Requirements

Blood Pressure Monitoring

• Check blood pressure every 5-10 minutes until stable, then every 15 minutes 2
• Blood pressure typically begins to decrease within 10-30 minutes after administration 6
• Average maximal decrease occurs in 10-80 minutes 3
• Duration of action is 2-4 hours 1, 6

Safety Parameters

• Hold or reduce hydralazine if diastolic BP falls below 80 mmHg to prevent maternal hypoperfusion 2, 6
• In high-risk patients (diabetes, age >60, coronary artery disease with heart failure), avoid diastolic BP below 60 mmHg 6
• For obstetrical patients, continuous fetal heart rate monitoring (cardiotocography) is essential 2

Expected Response and Adverse Effects

Hemodynamic Effects

• Mean arterial pressure falls by approximately 12 mmHg after the first bolus, 9 mmHg after the second, and 5 mmHg after the third 7
• Blood pressure control is achieved with bolus therapy alone in 89% of cases when protocol is followed 7

Common Adverse Effects

• Reflex tachycardia and palpitations occur significantly more often with hydralazine than labetalol 1, 8
• Headache, flushing, and vomiting are common 1
• Sodium and water retention may occur 6
• Maternal hypotension is possible but uncommon (2 of 100 patients in one trial) 8

Clinical Context and Limitations

When to Use Hydralazine

• Hydralazine is specifically indicated for hypertensive emergencies in eclampsia 1
• The International Society for the Study of Hypertension in Pregnancy considers it acceptable but not preferred as first-line for acute severe hypertension in pregnancy 2
• Treatment should be initiated within 60 minutes of severe hypertension onset 1

Why Hydralazine Is Less Desirable

• The American Heart Association notes that IV hydralazine has unpredictable response and prolonged duration of action, making it less desirable as first-line in most patients 1
• The European Society of Cardiology recommends more predictable IV agents with shorter half-lives (nicardipine, labetalol, clevidipine) for hypertensive emergencies 2, 6

Practical Considerations

Preparation and Administration

• Use immediately after the vial is opened 3
• Do not add to infusion solutions 3
• May discolor upon contact with metal; discard discolored solutions 3
• Inspect visually for particulate matter before administration 3

Timing of Repeat Doses

• Wait the full 20-30 minutes between doses to assess response 1, 2
• If hydralazine has already been given, wait 2-4 hours to assess full effect before additional treatment episodes 6
• Most patients can be transferred to oral hydralazine within 24-48 hours 3

Alternative Agents to Consider

• For non-obstetrical hypertensive emergencies, labetalol (20-80 mg IV bolus every 10 minutes) or nicardipine (5-15 mg/h IV) are preferred 1
• Labetalol causes less maternal tachycardia and palpitations than hydralazine 8
• For acute aortic dissection, use esmolol or labetalol instead 1