Hydralazine Drip Protocol for Severe Hypertension
Hydralazine is NOT typically administered as a continuous infusion for severe hypertension; instead, it should be given as intermittent IV boluses of 5-10 mg every 20-30 minutes, with the FDA-approved dosing being 20-40 mg repeated as necessary. 1, 2
Critical Context: When to Use Hydralazine
Hydralazine IV is specifically indicated for hypertensive emergencies in pregnancy (eclampsia/preeclampsia) and should NOT be first-line for most other hypertensive emergencies due to unpredictable blood pressure response and prolonged duration of action. 1, 3
Appropriate Clinical Scenarios:
- Obstetrical patients with severe hypertension (systolic BP ≥160 mmHg or diastolic BP ≥110 mmHg) 4, 1
- Treatment should be initiated within 60 minutes of onset in pregnancy 1
- For non-obstetrical hypertensive emergencies, consider labetalol, nicardipine, or clevidipine as first-line agents instead 1, 3
Dosing Protocol
Standard IV Bolus Regimen (Preferred):
For obstetrical patients:
- Initial dose: 5-10 mg IV bolus 4, 1
- Subsequent doses: 5-10 mg IV every 20-30 minutes as needed 4, 1
- Conservative approach: 5 mg initially, then 10 mg every 20-30 minutes to maximum 25 mg, repeated in several hours as necessary 1
- Maximum single dose: 30 mg 4
FDA-approved general dosing:
- Usual dose: 20-40 mg IV bolus, repeated as necessary 2
- Patients with marked renal damage may require lower doses 2
Continuous Infusion (NOT Standard Practice):
Continuous infusion hydralazine is NOT recommended for routine use and lacks established protocols. 5, 6 The evidence shows:
- One study in pregnancy found bolus dosing superior to continuous drip (65 minutes vs 186 minutes to control BP, using less total drug: 6.68 mg vs 20.07 mg) 5
- Pediatric case reports describe continuous infusion for afterload reduction in cardiac surgery, but responses were unsustainable 7
- No established dosing protocols exist for continuous infusion in adults outside of pregnancy 7, 5
Pharmacokinetics and Monitoring
Onset and Duration:
- Onset of action: 10-30 minutes after IV administration 1, 8, 2
- Peak effect: 10-80 minutes 2
- Duration of action: 2-4 hours (some sources report up to 12 hours for intermittent dosing) 4, 1, 8
Blood Pressure Targets:
- Reduce systolic BP by no more than 25% within the first hour 8
- If stable, further reduce to 160/100 mmHg over next 2-6 hours 8
- Cautiously normalize BP over following 24-48 hours 8
Monitoring Requirements:
- Check BP frequently after each dose 2
- Monitor for 2-4 hours post-administration due to prolonged duration 8
- Monitor heart rate for reflex tachycardia 4, 3
Adverse Effects and Contraindications
Common Adverse Effects:
- Reflex tachycardia (requires concurrent beta-blocker if used chronically) 4, 3
- Headache, flushing, palpitations 4, 1
- Nausea/vomiting 4, 2
- Unpredictable hypotension (17% experienced adverse events in one study, with hypotension most common) 6
Serious Concerns:
- Fetal distress secondary to abrupt maternal hypotension 4
- Side effects may mimic worsening pre-eclampsia (headache, palpitations) 4
- Drug-induced lupus-like syndrome (risk increases with total daily doses >150 mg) 3
- Increased intracranial pressure in pregnant women with cerebral edema 2
Contraindications:
- Advanced aortic stenosis 3
- Should not be added to infusion solutions 2
- Discolored solutions should be discarded 2
Critical Pitfalls to Avoid
Do NOT use hydralazine as first-line for non-obstetrical hypertensive emergencies - its unpredictable response makes it less desirable 1, 3
Do NOT use continuous infusion routinely - bolus dosing is more effective and uses less total drug 5
Do NOT use for asymptomatic hypertension in hospitalized patients - one study found 36% of doses were given for BP <180/110 mmHg, often inappropriately 9
Do NOT use as monotherapy for chronic hypertension - requires concurrent beta-blocker and diuretic to counteract reflex tachycardia and sodium retention 3
Avoid in acute aortic dissection - reflex tachycardia is harmful; use esmolol or labetalol instead 1