A 28-year-old multigravida at 30 weeks gestation is admitted with regular uterine contractions (4 per 10 minutes), cervical dilation of 2 cm, and intact membranes. Fetal monitoring shows normal heart rate. She is counselled on tocolytic agents. Which of the following is NOT an appropriate tocolytic agent for acute preterm labor management?

Explanation

## Tocolytic Agents in Preterm Labor ### Role of Tocolytics **Key Point:** Tocolytics do NOT prevent preterm birth; they delay delivery by 48 hours to allow time for: - Antenatal corticosteroid administration (fetal lung maturation) - Maternal transfer to tertiary center - Neuroprotection with magnesium sulfate (if <32 weeks) **High-Yield:** Tocolytics are **NOT** indicated for prolonged maintenance therapy — only for acute arrest of contractions to gain 48 hours. ### First-Line Tocolytic Agents **Mnemonic:** **CAIN** = **C**alcium channel blockers, **A**tosiban, **I**ndomethacin, **N**ifedipine (or NSAIDs). | Agent | Mechanism | Efficacy | Maternal SE | Fetal/Neonatal SE | Gestational Age Limit | |-------|-----------|----------|-------------|-------------------|----------------------| | **Nifedipine** | Calcium channel blocker | Delays 48h, neuroprotection | Headache, flushing, hypotension | Minimal | No limit; safe throughout | | **Indomethacin** | NSAID (COX inhibitor) | Delays 48h | GI upset, platelet dysfunction | PDA closure, oligohydramnios | Contraindicated >32 weeks | | **Atosiban** | Oxytocin V1a antagonist | Delays 48h | Fewer than β-blockers | Minimal | Safe throughout | | **Magnesium sulfate** | NMDA antagonist | Does NOT delay delivery | Flushing, hyperreflexia, pulmonary edema | Neuroprotection (cerebral palsy ↓) | <32 weeks | | **β-blockers** | β-adrenergic antagonist | Delays 48h | Tachycardia, tremor | Fetal bradycardia, hypoglycemia | Avoid if possible | ### Why Oxytocin is NOT a Tocolytic **Key Point:** Oxytocin is a **uterotonic** — it INCREASES uterine contractions and is used to **induce or augment** labor, NOT to arrest it. Oxytocin is the **opposite** of a tocolytic. **Clinical Pearl:** Confusing oxytocin with tocolytics is a classic exam trap. Oxytocin is used in preterm labor only if delivery is deemed inevitable or indicated (e.g., maternal hemorrhage, fetal distress requiring expedited delivery). ### Recommended Tocolytic Regimens 1. **First-line:** Nifedipine 20 mg PO, then 10–20 mg every 3–8 hours (max 160 mg/day) 2. **Alternative:** Indomethacin 50 mg PO/PR, then 25 mg every 6–8 hours (max 200 mg/day) — **only if <32 weeks** 3. **Second-line:** Atosiban 6.75 mg IV bolus, then 18 mg/hour infusion 4. **Neuroprotection (<32 weeks):** Magnesium sulfate 4 g IV loading, then 1 g/hour for 12 hours ### Contraindications & Cautions **Warning:** Indomethacin after 32 weeks causes: - Patent ductus arteriosus (PDA) closure in utero - Oligohydramnios (reduced amniotic fluid) - Neonatal renal dysfunction **High-Yield:** Nifedipine is the safest first-line agent with no absolute gestational age limit. ```mermaid flowchart TD A[Preterm labor 24-34 weeks]:::outcome --> B[Tocolytic indicated?]:::decision B -->|Yes| C[Administer corticosteroids]:::action C --> D[Choose tocolytic]:::decision D -->|<32 weeks| E[Nifedipine OR Indomethacin]:::action D -->|≥32 weeks| F[Nifedipine OR Atosiban]:::action E --> G[Add magnesium for neuroprotection]:::action F --> H[Delay 48 hours achieved]:::outcome I[Oxytocin]:::urgent -->|WRONG| J[Increases contractions - NOT tocolytic]:::urgent ``` **The incorrect statement:** "Oxytocin infusion — first-line agent for rapid arrest of preterm contractions" — oxytocin is a **uterotonic**, not a tocolytic. It causes contractions, not arrest.