PRN Hydralazine for Hypertensive Urgency
Hydralazine is NOT recommended as a first-line agent for hypertensive urgency due to its unpredictable blood pressure response, prolonged duration of action (2-4 hours), and inability to titrate effectively. 1
Why Hydralazine Should Be Avoided in Hypertensive Urgency
Key Limitations
Unpredictable response: Blood pressure begins to decrease within 10-30 minutes, but the magnitude of reduction is highly variable and cannot be reliably predicted, making safe blood pressure control difficult 1, 2
Prolonged duration: The hypotensive effect lasts 2-4 hours, creating risk of excessive blood pressure lowering without ability to reverse it 1, 2
Not titratable: Unlike continuous infusions (nicardipine, clevidipine), hydralazine is given as bolus doses that cannot be adjusted once administered 1
Reflex tachycardia: Can worsen myocardial ischemia in patients with coronary disease 3, 4
High adverse event rate: In hospitalized patients receiving IV hydralazine for non-urgent hypertension, 18% experienced adverse events, most commonly hypotension 5
Guideline Recommendations
The 2017 ACC/AHA guidelines explicitly state that hydralazine's "unpredictability of response and prolonged duration of action do not make hydralazine a desirable first-line agent for acute treatment in most patients" 1
Appropriate Management of Hypertensive Urgency
Definition and Approach
Hypertensive urgency: Severe BP elevation (>180/120 mmHg) WITHOUT acute target organ damage 1
Goal: Gradual BP reduction over 24-48 hours using oral agents, NOT immediate IV therapy 1, 6
Target: Reduce BP by no more than 25% within first hour, then to 160/100 mmHg over next 2-6 hours if stable 1
Preferred Oral Agents
For true hypertensive urgency (no end-organ damage), reinstitute or intensify oral antihypertensive therapy and arrange close follow-up 1
When Hydralazine IS Appropriate
Specific Indications
Eclampsia/preeclampsia is the primary indication where hydralazine remains appropriate 1, 3:
- Dosing for obstetric patients: 5-10 mg IV bolus initially, then 5-10 mg IV every 20-30 minutes as needed, maximum 25 mg 3
- Alternative obstetric dosing: 10 mg slow IV infusion (maximum initial dose 20 mg), repeat every 4-6 hours 1
Important Caveat for Pregnancy
The 2007 European Society of Hypertension guidelines note that "intravenous hydralazine should no longer be considered because its use is associated with more perinatal adverse effects than use of other drugs" 1, though it remains in some guidelines for eclampsia 1
Preferred Alternatives for Hypertensive Emergencies
If true hypertensive emergency exists (with acute organ damage):
Nicardipine: Initial 5 mg/h IV, increase by 2.5 mg/h every 5 minutes to maximum 15 mg/h - easily titratable 1, 4
Clevidipine: Initial 1-2 mg/h IV, doubling every 90 seconds until BP approaches target - ultra-short acting 1, 4
Labetalol: 0.3-1.0 mg/kg (maximum 20 mg) slow IV every 10 minutes - but contraindicated with bradycardia, heart block, or reactive airway disease 1, 4
FDA-Approved Dosing (If Used)
Per FDA labeling, when hydralazine must be used 7:
- Dose: 20-40 mg IV or IM, repeated as necessary
- Onset: Blood pressure may begin falling within minutes, with maximal decrease at 10-80 minutes
- Monitoring: Check BP frequently throughout 2-4 hour duration of action
- Preparation: Use immediately after opening vial; do not add to infusion solutions; discard discolored solutions
Clinical Pitfalls
Inappropriate use: A prospective study found that 96% of hospitalized patients receiving IV hydralazine had NO urgent hypertensive condition, representing widespread misuse 5
Variable response: In the same study, systolic BP reduction ranged widely (24 ± 29 mmHg), with 11 patients developing hypotension 5
Distinguishing urgency from emergency: Always assess for acute organ damage (encephalopathy, acute coronary syndrome, pulmonary edema, stroke, acute renal failure, aortic dissection) before choosing IV therapy 1