What is the recommended initial dose of labetolol (Labetalol) infusion for managing preeclampsia?

Labetalol Infusion Dosing for Preeclampsia

For preeclampsia requiring intravenous therapy, the recommended initial dose of labetalol infusion is 2 mg/minute, administered as a continuous infusion prepared by diluting 200 mg of labetalol in 200 mL of IV fluid (1 mg/mL) and infusing at 2 mL/minute. 1

Preparation of Labetalol Infusion

• Prepare the infusion by adding 200 mg of labetalol (either two 20-mL vials or one 40-mL vial) to 160 mL of compatible IV fluid to create a 200 mL solution with concentration of 1 mg/mL 1
• Alternatively, add 200 mg of labetalol to 250 mL of compatible IV fluid to create a solution of approximately 2 mg/3 mL, which should be administered at 3 mL/minute to deliver approximately 2 mg/minute 1
• Compatible IV fluids include Ringer's solution, Lactated Ringer's, 5% Dextrose, and 0.9% Sodium Chloride 1

Administration and Monitoring

• The rate of infusion should be adjusted according to blood pressure response at the physician's discretion 1
• The immediate goal is to decrease mean blood pressure by 15-25% with target systolic blood pressure of 140-150 mmHg and diastolic blood pressure of 90-100 mmHg 2
• For severe preeclampsia, the American College of Obstetricians and Gynecologists recommends targeting systolic blood pressure <160 mmHg and diastolic blood pressure <105 mmHg 3
• Blood pressure should be monitored continuously during and after completion of the infusion 1
• The effective intravenous dose is usually in the range of 50 to 200 mg, with a total dose of up to 300 mg sometimes required 1
• The cumulative dose should not exceed 800 mg/24h to prevent fetal bradycardia 3

Alternative Dosing Method: Repeated IV Injections

• If continuous infusion is not feasible, labetalol can be administered as repeated IV injections 1
• Begin with an initial dose of 20 mg (0.25 mg/kg for an 80 kg patient) by slow IV injection over 2 minutes 1
• Measure blood pressure immediately before injection and at 5 and 10 minutes after injection 1
• Additional injections of 40 mg or 80 mg can be given at 10-minute intervals until desired blood pressure is achieved or a total of 300 mg has been administered 1
• Maximum effect usually occurs within 5 minutes of each injection 1

Important Considerations and Cautions

• Patients should remain in a supine position during administration as substantial falls in blood pressure on standing should be expected 1
• Avoid rapid or excessive falls in either systolic or diastolic blood pressure 1
• Labetalol is considered safe and effective for IV treatment of severe preeclampsia 2
• Caution is advised with initial IV dosing - one case report suggested that a 50 mg IV bolus dose resulted in rapid blood pressure reduction and fetal death; an initial dose of 5-10 mg was recommended if bolus administration is necessary 4
• Monitor for signs of pulmonary edema, which may occur in patients with severe preeclampsia, particularly those with significant positive fluid balance 5
• Labetalol is contraindicated in patients with second or third-degree heart block, bradycardia, decompensated heart failure, and reactive airways disease or COPD 3, 6

Transition to Oral Therapy

• Once satisfactory response is obtained, the infusion should be discontinued and oral labetalol therapy initiated 1
• Begin oral therapy when supine diastolic blood pressure has begun to rise 1
• The recommended initial oral dose is 200 mg, followed in 6-12 hours by an additional dose of 200 or 400 mg depending on blood pressure response 1

Labetalol has been shown to be as effective as nifedipine for controlling blood pressure in preeclampsia, though some studies suggest nifedipine may achieve target blood pressure more rapidly 7, 8.