Oral Hydralazine Dosing for Preeclampsia
For oral hydralazine in preeclampsia, the recommended dosing is 10-25 mg every 6-8 hours, with a maximum daily dose of 200-300 mg. While hydralazine has been used for preeclampsia management, current evidence suggests it is not a first-line agent for oral therapy in this condition.
Dosing Recommendations
- Initial oral dose: 10-25 mg
- Frequency: Every 6-8 hours
- Maximum daily dose: 200-300 mg (divided doses)
- Onset of action: 10-30 minutes
- Duration of effect: 2-4 hours
Efficacy and Limitations
Hydralazine has been widely used for severe preeclampsia, but evidence indicates it is inferior to other agents 1. The unpredictability of response and prolonged duration of action make hydralazine less desirable as a first-line agent for most patients. Blood pressure begins to decrease within 10-30 minutes after administration, and the effect typically lasts 2-4 hours 1.
Preferred Alternatives
Current guidelines suggest the following medications are preferred over oral hydralazine for preeclampsia:
- Methyldopa: First-line agent with the best safety record; dose 750 mg to 4 g per day in three or four divided doses 1
- Labetalol: 100 mg twice daily up to 2400 mg per day 1
- Nifedipine: More effective than hydralazine in controlling blood pressure in severe preeclampsia with fewer administrations needed 2
Monitoring and Precautions
When using oral hydralazine:
- Monitor blood pressure every 15-30 minutes after initial dose
- Target blood pressure: reduce systolic BP to <160 mmHg and diastolic BP to <110 mmHg 3
- Watch for common side effects: headache, palpitations, tachycardia, nausea/vomiting, and flushing 3
- Continuous fetal heart rate monitoring is necessary during treatment 3
Important Considerations
- Hydralazine can cause a rapid, unpredictable fall in blood pressure that may compromise uteroplacental perfusion 4
- Avoid continuous intravenous infusion of hydralazine, as this has been associated with fetal distress requiring cesarean delivery 4
- Hydralazine has been shown to be excreted in breast milk 5
- Animal studies indicate hydralazine is teratogenic at high doses, but clinical experience does not include positive evidence of adverse effects on the human fetus 5
Clinical Decision Algorithm
- Confirm diagnosis of preeclampsia with BP ≥140/90 mmHg after 20 weeks gestation with proteinuria
- For non-severe hypertension (140-159/90-109 mmHg):
- First choice: Methyldopa 250-500 mg orally three times daily
- Second choice: Labetalol 100-400 mg orally twice daily
- Third choice: Hydralazine 10-25 mg orally every 6-8 hours
- For severe hypertension (≥160/110 mmHg):
- Use IV medications rather than oral therapy
- Consider hospitalization and preparation for delivery
Remember that delivery is the only definitive treatment for preeclampsia, and antihypertensive treatment is primarily used to prevent maternal complications while preparing for delivery or prolonging pregnancy when appropriate 1.