Hydralazine Drip Protocol
Hydralazine should NOT be administered as a continuous infusion for severe hypertension—the FDA-approved and guideline-recommended approach is intermittent IV bolus dosing of 20-40 mg repeated as necessary every 4-6 hours, not a continuous drip. 1, 2
Why Continuous Infusion Is Not Standard Practice
- The FDA label explicitly states that hydralazine "should not be added to infusion solutions" and recommends rapid IV bolus injection directly into the vein 1
- Hydralazine is "not a desirable first-line agent for acute treatment in most patients" due to its unpredictable response and prolonged duration of action (2-4 hours) 3
- Limited evidence exists for continuous infusion hydralazine, with one pediatric case report showing only brief, non-sustained blood pressure reduction 4
- A comparative study in obstetric emergencies demonstrated that bolus injection was superior to continuous drip, requiring less time (65 vs 186 minutes) and lower total doses (6.7 vs 20 mg) to achieve blood pressure control 5
FDA-Approved Bolus Dosing Protocol
- Initial dose: 20-40 mg IV bolus via rapid injection directly into the vein 1
- Repeat dosing: Every 4-6 hours as necessary 2, 1
- Patients with marked renal damage may require lower doses 1
- Blood pressure begins to fall within 10-30 minutes, with maximal decrease occurring at 10-80 minutes 1, 2
- The hypotensive effect persists for 2-4 hours after each administration 2
Critical Monitoring Requirements
- Check blood pressure frequently during the 2-4 hour duration of action 2
- Monitor at specific intervals: 10-30 minutes, 1 hour, and 2-4 hours after each dose 6
- Reduce systolic blood pressure by no more than 25% within the first hour to avoid cerebral ischemia 2
- After initial reduction, if stable, further reduce to 160/100 mmHg over the next 2-6 hours, then cautiously to normal over 24-48 hours 2
Important Caveats and Pitfalls
- Hydralazine causes reflex tachycardia, making it problematic in patients with bradycardia 3
- Avoid in patients with increased intracranial pressure, as lowering blood pressure may worsen cerebral ischemia 1
- The response is highly variable and unpredictable—one study showed blood pressure changes of 24/9 ± 29/15 mmHg with 11% of patients experiencing hypotension 7
- Hydralazine is frequently misused for non-urgent hypertension (36% of doses given for BP <180/110 mmHg in one study), which is inappropriate 8
- Use immediately after opening the vial; discard discolored solutions as hydralazine may discolor upon contact with metal 1
Preferred Alternative Agents for Continuous Infusion
- Nicardipine infusion (initial 5 mg/h, increasing every 5 minutes by 2.5 mg/h to maximum 15 mg/h) is preferred for hypertensive emergencies requiring continuous control 3
- Clevidipine (initial 1-2 mg/h with careful titration) is another suitable continuous infusion option 3
- These agents provide more predictable, titratable blood pressure control compared to intermittent hydralazine boluses 3