A 32-year-old primigravida at 28 weeks of gestation presents with vaginal bleeding and uterine contractions (3–4 per 10 minutes). Cervical examination shows 2 cm dilation. Fetal heart rate is reassuring. What is the drug of choice for tocolysis in this patient?

Explanation

## Tocolytic Agents in Preterm Labor **Key Point:** Nifedipine (a calcium channel blocker) is the first-line tocolytic agent for preterm labor in most clinical settings, including India, due to superior safety profile and efficacy. ### Mechanism of Action Nifedipine inhibits L-type calcium channels in myometrial smooth muscle, reducing intracellular Ca²⁺ and preventing actin-myosin cross-bridging, thereby suppressing uterine contractions. ### Comparison of Tocolytic Agents | Agent | Class | Efficacy | Safety Profile | Maternal Side Effects | Fetal/Neonatal Effects | First-Line? | |-------|-------|----------|-----------------|----------------------|----------------------|-------------| | **Nifedipine** | Calcium channel blocker | Good | Excellent | Headache, flushing, hypotension (mild) | Minimal | **Yes** | | **Indomethacin** | NSAID (COX inhibitor) | Good | Moderate | GI upset, headache | PDA closure, oligohydramnios (>32 wks) | No (avoid >32 wks) | | **Magnesium sulphate** | Membrane stabilizer | Moderate | Good | Flushing, weakness, nausea | Minimal | Adjunct/rescue | | **Terbutaline** | β₂-agonist | Good | Fair | Tachycardia, tremor, hyperglycemia | Tachycardia, hyperglycemia | No (2nd-line) | ### High-Yield Facts **High-Yield:** Nifedipine is preferred because: 1. No maternal cardiovascular contraindications (unlike β₂-agonists) 2. No fetal ductal closure risk (unlike NSAIDs) 3. Oral or sublingual administration (convenient) 4. Lower maternal mortality compared to β₂-agonists **Clinical Pearl:** At 28 weeks (as in this case), nifedipine is ideal. Indomethacin is contraindicated after 32 weeks due to risk of premature ductus arteriosus closure and oligohydramnios. **Warning:** Magnesium sulphate is NOT a tocolytic — it is used for seizure prophylaxis in preeclampsia and neuroprotection in preterm labor <32 weeks, not for uterine relaxation. ### Dosing Regimen (Nifedipine) - **Loading:** 20 mg orally, repeat 20 mg after 30 minutes if needed - **Maintenance:** 10–20 mg orally every 4–6 hours for up to 48 hours - **Goal:** Delay delivery by 48 hours to allow corticosteroid administration and in-utero transfer [cite:ACOG Committee Opinion 931, Williams Obstetrics 26e Ch 16]