What is the recommended dose of nifedipine (calcium channel blocker) to prevent preterm labor?

Nifedipine Dosing for Prevention of Preterm Labor

For prevention of preterm labor, the recommended nifedipine regimen is 10 mg orally every 15 minutes for up to four doses in the first hour (maximum 40 mg), followed by 60-80 mg of slow-release nifedipine daily for 48 hours, then 60 mg daily maintenance until 36 weeks gestation. 1, 2

Initial Loading Dose

• Initial loading with immediate-release nifedipine capsules: 10 mg orally every 15-20 minutes for up to 4 doses (maximum 40 mg in the first hour) 1, 2
• Alternative loading regimen: 20 mg loading dose, which may be repeated after 30 minutes if contractions persist 3

Maintenance Dosing

• After initial loading, switch to slow-release formulation: 60-80 mg daily for the first 48 hours 3, 1
• For ongoing tocolysis: 60 mg daily until 36 weeks gestation 3, 4
• Higher maintenance doses (80-120 mg daily) may be used in some cases but don't appear to offer significant advantages over lower doses for achieving uterine quiescence at 48 hours 3

Administration Considerations

• Nifedipine should be administered orally, not sublingually (sublingual administration increases risk of sudden hypotension) 5
• Tablets should be swallowed whole, not bitten or divided, when using extended-release formulations 6
• Administer on an empty stomach for optimal absorption 6

Monitoring and Efficacy Assessment

• Monitor maternal blood pressure closely, especially during the first hour of treatment 5, 2
• Therapeutic plasma concentration to achieve tocolysis is approximately 67 ng/mL 1
• Success is defined as cessation of contractions and prevention of delivery for at least 48 hours 3, 4
• In most cases (86.8%), pregnancy can be extended for more than 48 hours after the first dose 4

Precautions and Side Effects

• Use with caution when combined with magnesium sulfate due to risk of precipitous blood pressure drop 5, 7
• Common side effects include dizziness (39.5%), headache (18.4%), and flushing 4, 5
• Monitor for hypotension (BP ≤ 90/60 mmHg), which occurs in approximately 5% of patients 2

Alternative Approaches

• If standard nifedipine tocolysis is insufficient, some evidence suggests combining with sildenafil citrate may enhance effectiveness (25 mg sildenafil vaginally every 8 hours) 8
• If nifedipine fails to achieve tocolysis within 48 hours, consider alternative tocolytics or reassessment of labor status 3

Important Considerations

• Nifedipine is not FDA-approved specifically for preterm labor management but is used off-label for this indication 5
• For hypertensive emergencies in pregnancy, a different dosing regimen is used (10-20 mg short-acting nifedipine with possible repeat in 30 minutes if needed) 7
• The goal of tocolysis is to allow time for administration of corticosteroids for fetal lung maturity, especially in pregnancies ≤34 weeks gestation 7