Is isoxsuprine (a tocolytic agent) still recommended for use in active preterm labor?

Isoxsuprine Should Not Be Used for Active Preterm Labor

Isoxsuprine is not recommended as a tocolytic agent for active preterm labor, as current evidence-based guidelines support the use of nifedipine or indomethacin as first-line tocolytic agents instead. 1, 2

Current Guideline-Based Recommendations

The American College of Obstetricians and Gynecologists (ACOG) specifically recommends nifedipine and indomethacin as the preferred tocolytic agents to delay delivery for 48-72 hours in women with preterm labor and intact membranes after 26 weeks of gestation. 1, 2 These agents are recommended to allow time for:

• Administration of antenatal corticosteroids 1, 2
• Maternal transfer to a tertiary care facility with appropriate neonatal intensive care capabilities 1, 2

Why Isoxsuprine Is Inferior

While isoxsuprine is a beta-mimetic agent that has been historically used for tocolysis, comparative research demonstrates that nifedipine is significantly more effective:

• Nifedipine achieved successful tocolysis in 81.25% of patients compared to 70% with isoxsuprine 3
• Nifedipine was twice as effective as isoxsuprine as a tocolytic agent (P value 0.006) 4
• Nifedipine prolonged pregnancy by an average of 25 days versus 19.18 days with isoxsuprine 3
• Nifedipine had particularly higher efficacy when started with the earliest signs of preterm labor 4

Safety Profile Considerations

Maternal side effects are comparable or worse with isoxsuprine:

• Hypotension and tachycardia are common with both agents 3
• Cardiac side effects were significantly higher with isoxsuprine compared to other beta-mimetics like ritodrine 5
• Pulmonary edema and severe hypotension may require discontinuation of therapy 3
• Isoxsuprine has a higher failure rate (22.22%) compared to other beta-mimetics 5

Neonatal Outcomes Favor Calcium Channel Blockers

Nifedipine demonstrates superior neonatal outcomes compared to beta-mimetics (including isoxsuprine):

• Reduced respiratory distress syndrome (RR 0.64) 6
• Reduced necrotizing enterocolitis (RR 0.21) 6
• Reduced intraventricular hemorrhage (RR 0.53) 6
• Reduced admissions to neonatal intensive care unit (RR 0.74) 6
• Reduced preterm birth before 37 weeks (RR 0.89) and very preterm birth (RR 0.78) 6

Clinical Algorithm for Tocolytic Selection

When managing active preterm labor between 24-34 weeks:

1. First-line tocolytic: Nifedipine or indomethacin 1, 2
2. Concurrent therapy: Administer antenatal corticosteroids (24-34 weeks) 2
3. Neuroprotection: Consider magnesium sulfate if <32 weeks 2
4. Avoid: Beta-mimetics like isoxsuprine due to inferior efficacy and safety profile 3, 4, 6

Important Caveats

• Tocolytic therapy is generally not recommended when delivery would be beneficial for maternal or fetal indications 1
• Despite delaying delivery, no tocolytic has been consistently shown to improve perinatal mortality 1, 6
• The primary benefit of tocolytics is gaining time for corticosteroid administration and maternal transfer, not preventing preterm birth itself 1
• Active preterm labor is a contraindication to exercise, but this does not mean complete bed rest—activities of daily living should be maintained 7