Is Hydralazine Safe for High Blood Pressure in Pregnancy?
Hydralazine is used to treat high blood pressure during pregnancy, particularly in cases of preeclampsia or hypertensive emergencies. It lowers blood pressure by relaxing blood vessel walls as a direct arterial vasodilator. The American College of Obstetricians and Gynecologists (ACOG) recommends it as an intravenous option for acute severe hypertension in pregnancy, alongside drugs like labetalol and nifedipine.[1]
What Pregnancy Category Is Hydralazine?
Hydralazine is FDA Pregnancy Category C. Animal studies show adverse effects at high doses, but no adequate human studies exist. It is still widely used because benefits often outweigh risks in maternal hypertension, with clinical experience supporting its safety in the second and third trimesters.[2][3]
How Is It Typically Administered in Pregnancy?
- Intravenous: Preferred for rapid control in hospital settings, starting at 5-10 mg every 20-30 minutes up to 20 mg, with monitoring for hypotension.
- Oral: For ongoing management, doses range from 25-100 mg 3-4 times daily.
It acts within 10-20 minutes IV and 1-2 hours orally, lasting 3-6 hours IV and up to 12 hours orally.[4]
What Risks and Side Effects Occur?
Common side effects include headache, tachycardia, flushing, and nausea. In pregnancy, risks involve maternal hypotension (potentially reducing placental blood flow) and fetal tachycardia. Rare lupus-like syndrome can develop with long-term use. Neonatal thrombocytopenia is reported but uncommon. No strong link to congenital malformations exists in human data.[5][6]
How Does It Compare to Other Pregnancy Hypertension Treatments?
| Drug | Route | Onset | Pregnancy Use Notes |
|---------------|------------|-------------|--------------------------------------|
| Hydralazine | IV/Oral | Fast (IV) | First-line for acute severe HTN |
| Labetalol | IV/Oral | Fast (IV) | Preferred first-line; beta-blocker |
| Nifedipine | Oral/IV | 5-15 min | Calcium channel blocker; avoids reflex tachycardia |
| Methyldopa | Oral | Slow | First-line chronic; central alpha agonist |
Hydralazine is favored IV when labetalol is unavailable or contraindicated (e.g., asthma).[1][7]
What Clinical Evidence Supports Its Use?
Observational studies and guidelines cite success in thousands of pregnancies. A 2017 meta-analysis found no increased malformation risk versus controls. ACOG and WHO list it as essential for preeclampsia management in resource-limited settings.[3][8]
When Should It Be Avoided?
Avoid in first trimester if possible due to limited data; use only if essential. Contraindicated in coronary artery disease, mitral valve rheumatic heart disease, or hypersensitivity. Monitor fetal heart rate and blood pressure closely.[2]
[1]: ACOG Practice Bulletin No. 222: Gestational Hypertension and Preeclampsia
[2]: FDA Label for Hydralazine
[3]: Drugs in Pregnancy and Lactation, 12th Ed. (Hydralazine entry)
[4]: Lexicomp: Hydralazine
[5]: Briggs' Drugs in Pregnancy and Lactation
[6]: Cochrane Review: Antihypertensives in Pregnancy
[7]: SMFM Consult: Severe Hypertensive Disorders
[8]: WHO Essential Medicines List for Pregnancy