What is the most appropriate medication for acute treatment of hypertension in a 27-year-old primigravida (first-time pregnant woman) at 36 weeks of gestation with symptoms suggestive of preeclampsia, including headache, blurred vision, and severe hypertension (blood pressure 160/110 mmHg)?

Acute Treatment of Severe Hypertension in Preeclampsia at 36 Weeks

For this patient with severe preeclampsia (BP 160/110 mmHg with headache and visual symptoms), hydralazine (Option C) is the most appropriate first-line medication for acute blood pressure control, though oral nifedipine and intravenous labetalol are equally acceptable alternatives according to current international guidelines.

Clinical Context and Urgency

This 36-week pregnant patient presents with severe hypertension (≥160/110 mmHg) accompanied by neurological symptoms (headache, blurred vision) and proteinuria, meeting criteria for severe preeclampsia requiring urgent treatment within 60 minutes of the first severe reading 1. Blood pressure ≥160/110 mmHg represents a hypertensive emergency in pregnancy and serves as a surrogate marker for stroke risk 1.

First-Line Medication Options

The most recent international guidelines consistently recommend three equally acceptable first-line agents for acute severe hypertension in pregnancy 1:

• Oral nifedipine (immediate-release): 10-20 mg orally, repeatable every 20-30 minutes to maximum 30 mg 1, 2
• Intravenous labetalol: 20 mg IV bolus, followed by 40 mg, then 80 mg every 10 minutes to maximum cumulative dose of 220-300 mg 1, 3
• Intravenous hydralazine: 5 mg IV, followed by 5-10 mg every 20-30 minutes 1

Why Hydralazine (Option C) is Correct

Hydralazine has been the traditional first-line agent for acute severe hypertension in pregnancy, particularly in North America, and remains widely recommended in current guidelines 1. While recent evidence suggests oral nifedipine and IV labetalol may have superior safety profiles, hydralazine maintains its position as an acceptable first-line option 1.

Evidence Supporting Hydralazine:

• Listed as first-line agent by ISSHP 2018 guidelines for acute severe hypertension 1
• Effective in rapidly lowering blood pressure in hypertensive emergencies of pregnancy 4
• Equivalent efficacy to nifedipine in achieving target blood pressure (median 40 minutes for both agents) 5

Important Caveats with Hydralazine:

Hydralazine is associated with more maternal adverse effects compared to labetalol or nifedipine, including maternal hypotension, placental abruption, maternal oliguria, and fetal tachycardia, requiring close monitoring of both maternal BP and fetal wellbeing 1. The American Heart Association now suggests avoiding IV hydralazine as first-line therapy due to more adverse perinatal outcomes 3. However, it remains widely used and guideline-recommended 1.

Why Other Options Are Incorrect

Option A (Clonidine):

Not recommended for acute hypertensive emergencies in pregnancy. Clonidine has no established role in acute management of severe hypertension in pregnancy and is not mentioned in any current guidelines for this indication 1.

Option B (Methyldopa):

Inappropriate for acute management due to slow onset of action 4. Methyldopa is recommended only for chronic/maintenance blood pressure control in pregnancy, not acute emergencies 1, 6. It takes hours to achieve therapeutic effect, making it unsuitable when urgent BP reduction is required within 60 minutes 1.

Option D (Sodium Nitroprusside):

Should only be used as last resort for extreme emergencies when other agents fail 1. Prolonged use is associated with fetal cyanide poisoning and increased maternal intracranial pressure (potentially worsening cerebral edema in preeclampsia) 1. It should be used for the shortest possible duration only if BP cannot be controlled by other means 1.

Optimal Treatment Algorithm

For this patient, the recommended approach is 1, 3:

1. Immediate treatment (within 60 minutes of first severe reading) with one of three first-line agents:

   • IV hydralazine 5 mg, repeat 5-10 mg every 20 minutes 1
   • OR oral nifedipine 10-20 mg, repeat every 20-30 minutes (maximum 30 mg) 1, 2
   • OR IV labetalol 20 mg, then 40 mg, then 80 mg every 10 minutes 1, 3

2. Target blood pressure: Systolic 140-150 mmHg and diastolic <105-110 mmHg to prevent maternal stroke while maintaining placental perfusion 3

3. Magnesium sulfate prophylaxis: This patient requires MgSO₄ for seizure prophylaxis given severe hypertension with neurological symptoms 1

4. Continuous monitoring: Maternal BP every 5-10 minutes and continuous fetal heart rate monitoring during acute treatment 3

5. Delivery planning: At 36 weeks with severe preeclampsia and neurological symptoms, delivery should be planned once BP is stabilized 1

Critical Safety Considerations

• Avoid combining nifedipine with magnesium sulfate due to risk of precipitous hypotension from potential synergism 1, 2, 3
• Never use sublingual nifedipine due to uncontrolled hypotension risk 1, 2
• Labetalol is contraindicated in asthma, heart block, or decompensated heart failure 3
• Avoid excessive BP reduction as treatment-induced falls in mean arterial pressure correlate with small-for-gestational-age infants 2

Contemporary Practice Shift

Recent high-quality evidence suggests oral nifedipine may be superior to hydralazine with fewer maternal side effects and equal efficacy 7, 5. A 2019 network meta-analysis found nifedipine superior to hydralazine (OR 4.13) for successful treatment without increased cesarean delivery or maternal side effects 7. However, hydralazine remains guideline-recommended and widely used, particularly in North American practice 1.