Can a patient with hypertensive urgency in the Emergency Room (ER) be given a second dose of Hydralazine (hydrochloride) 20 mg intravenous (IV) if the initial dose does not adequately reduce blood pressure?

Can a Second Dose of Hydralazine 20 mg IV Be Given for Hypertensive Urgency?

Yes, a second dose of hydralazine 20 mg IV can be given and is explicitly supported by FDA labeling, which states "repeat as necessary" for the usual 20-40 mg dose, though hydralazine should not be used as first-line therapy for hypertensive urgency in the first place. 1

Critical Distinction: Urgency vs. Emergency

Before administering any IV hydralazine, you must first clarify whether this is truly a hypertensive urgency or an emergency:

• Hypertensive urgency = severe BP elevation (>180/120 mmHg) WITHOUT acute target organ damage 2
• Hypertensive emergency = severe BP elevation WITH evidence of new or worsening target organ damage (encephalopathy, ICH, acute MI, acute LV failure, aortic dissection, acute renal failure, eclampsia) 2

If this is truly hypertensive urgency (no target organ damage), IV hydralazine should not be used at all. 3 These patients should be managed with oral antihypertensives and gradual BP reduction over 24-48 hours, not immediate IV therapy. 2

If This Is Actually a Hypertensive Emergency

Dosing Parameters for Hydralazine

If you have already given one dose and are considering a second:

• FDA-approved dosing: Initial 10-20 mg via slow IV infusion, repeated every 4-6 hours as needed 2, 1
• Maximum initial dose: 20 mg 2
• Timing between doses: Wait 4-6 hours before repeating 2
• Onset of action: BP begins to decrease within 10-30 minutes 2, 4
• Duration of effect: 2-4 hours 2, 3, 4

Why Hydralazine Is Problematic

The ACC/AHA guidelines explicitly state that hydralazine's unpredictability of response and prolonged duration of action do not make it a desirable first-line agent for acute treatment in most patients. 2, 3 Here's why:

• Unpredictable BP response: Variable magnitude of BP reduction makes safe control difficult 3
• Cannot titrate: Given as bolus doses that cannot be adjusted once administered, unlike continuous infusions 3
• Prolonged duration: Hypotensive effect lasts 2-4 hours with no ability to reverse excessive BP lowering 3
• Risk of overshoot hypotension: Can cause excessive BP reduction without the ability to stop the effect 2

Preferred Alternatives for Hypertensive Emergency

You should strongly consider switching to a titratable agent rather than giving a second hydralazine dose: 3

• Nicardipine: Initial 5 mg/h IV, increase by 2.5 mg/h every 5 minutes to maximum 15 mg/h 2, 3
• Clevidipine: Initial 1-2 mg/h IV, double every 90 seconds until BP approaches target 2, 3
• Labetalol: 0.3-1.0 mg/kg (maximum 20 mg) slow IV every 10 minutes 2, 3

These agents allow precise titration and can be stopped immediately if BP drops too much. 3

The One Exception: Pregnancy

Hydralazine IS appropriate as first-line therapy for severe hypertension in pregnancy/eclampsia: 3, 4

• Obstetric dosing: 5 mg IV bolus initially, then 10 mg IV every 20-30 minutes as needed, maximum 25 mg per episode 4
• Alternative obstetric dosing: 10 mg slow IV infusion (maximum initial dose 20 mg), repeated every 4-6 hours 4
• Treatment should be initiated within 60 minutes of onset 4

Critical Monitoring Requirements

If you proceed with a second hydralazine dose:

• Check BP at: 10-30 minutes, 1 hour, and 2-4 hours after each dose 4
• Watch for reflex tachycardia: May require concomitant beta-blocker 4
• Monitor for overshoot hypotension: Particularly dangerous as the effect cannot be reversed 3
• Common side effects: Headache, palpitations, flushing, vomiting 4

Bottom Line Algorithm

1. Confirm this is a hypertensive emergency (target organ damage present) - if not, use oral agents instead 2
2. If pregnancy-related: Hydralazine is appropriate; give 10 mg IV, can repeat every 20-30 minutes up to 25 mg total 4
3. If non-obstetric emergency: Switch to nicardipine, clevidipine, or labetalol for better control 3
4. If you must use hydralazine: Wait 4-6 hours between doses, use 10-20 mg per dose, monitor closely for overshoot hypotension 2, 1