Hydralazine Administration Protocol for Severe Hypertension
For severe hypertension management, hydralazine is administered as an initial 10 mg via slow IV infusion (maximum initial dose 20 mg), which can be repeated every 4-6 hours as needed. 1
IV Administration Details
Dosing Protocol
- Initial dose: 10 mg via slow IV infusion (maximum initial dose 20 mg)
- Onset of action: 10-30 minutes
- Duration of action: 2-4 hours
- Repeat dosing: Every 4-6 hours as needed to maintain blood pressure control
Alternative Dosing in Special Situations
- For preeclampsia: 5 mg IV bolus, then 10 mg every 20-30 minutes to a maximum of 25 mg, repeated in several hours as necessary 1
- FDA-labeled dosing: 20-40 mg IV, repeated as necessary with close blood pressure monitoring 2
Administration Considerations
- Blood pressure begins to decrease within 10-30 minutes after administration
- Effect typically lasts 2-4 hours
- Parenteral solutions should be inspected for particulate matter and discoloration before administration
- Hydralazine may discolor upon contact with metal; discolored solutions should be discarded 2
- Should be used immediately after opening the vial
- Should not be added to infusion solutions 2
Clinical Considerations
Monitoring
- Blood pressure should be checked frequently
- Blood pressure may begin to fall within minutes after injection
- Average maximal decrease occurs in 10-80 minutes 2
- Intra-arterial BP monitoring may be beneficial to prevent "overshoot" hypotension
Cautions and Limitations
Hydralazine is no longer considered a first-line agent for hypertensive emergencies due to:
- Unpredictability of response
- Prolonged duration of action 1
- Risk of precipitous blood pressure drops
Continuous IV infusion is not recommended, as studies have shown rapid uncontrolled decline in blood pressure with this method 3
Adverse Effects
- Tachycardia
- Flushing
- Headache
- Vomiting
- Potential aggravation of angina 1
- Palpitations (more common with hydralazine than labetalol) 4
Special Populations
Pregnancy
- While historically used in preeclampsia/eclampsia, recent guidelines note that IV labetalol or oral nifedipine may be preferred options 1
- A 2023 study found that IV hydralazine achieved target blood pressure faster than labetalol in severe gestational hypertension (45.8 vs 72.7 minutes) and required fewer doses (1.7 vs 3.7) 5
- However, hydralazine had more maternal side effects, though not severe enough to warrant discontinuation 5
Transition to Oral Therapy
- Most patients can be transferred to oral hydralazine within 24-48 hours 2
- For chronic management in heart failure, oral dosing is typically 25-50 mg, 3-4 times daily with a maximum of 300 mg daily in divided doses 1