Tocolytic Therapy for Preterm Labor aka. Stop Labor by using Nifedipine (Adalat) and Terbutaline (Bricanyl)

quick-reference table summarizing the common protocol for nifedipine (Adalat) as a tocolytic in preterm labor:

Note: Always monitor maternal blood pressure, pulse, and signs of pulmonary edema. If nifedipine is not effective or cannot be used, consider terbutaline (Bricanyl) according to institutional protocols.

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Tocolytic Therapy for Preterm Labor

Preterm labor is defined as regular uterine contractions accompanied by cervical change occurring before 37 completed weeks of gestation. Tocolysis aims to delay delivery long enough to allow the administration of corticosteroids for fetal lung maturity and/or transfer to a higher-level care facility. Although no single tocolytic completely prevents preterm birth, certain agents help prolong pregnancy by at least 48 hours, benefiting both fetal lung maturity and patient management.

Before administering any tocolytic, ensure:

1. No obstetric complications such as antepartum hemorrhage or severe hypertension.
2. No chorioamnionitis.
3. No fetal distress.
4. No significant fetal anomalies precluding continuation of pregnancy.
5. No maternal medical disorder that contraindicates pregnancy continuation or the specific tocolytic.

Two commonly used agents in Thailand for preterm labor are nifedipine (Adalat)—a calcium channel blocker—and terbutaline (Bricanyl)—a beta-2 adrenergic agonist. Below are step-by-step regimens and key clinical points for each.

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1. Nifedipine (Adalat)

Mechanism of Action

• Blocks calcium channels in smooth muscle cells, reducing intracellular calcium and inhibiting uterine contractions.

Common Protocol

1. Initial (Loading) Dose
   • Adalat 5 mg (Immediate-release)
   • Give 2 tablets (total 10 mg) orally every 15 minutes
   • For a total of 4 doses (maximum loading: 40 mg)
2. Short-term Maintenance (Titration)
   • Adalat 5 mg tablets
   • 5 tablets (25 mg) orally every 4 hours
   • For a total of 4 doses
3. Long-term Maintenance
   • Adalat SR 20 mg (Sustained-release)
   • 1 tablet orally every 8 hours
   • Continue for 7 days
4. If Nifedipine Fails or is Contraindicated
   • Switch to a beta-agonist such as terbutaline (Bricanyl) (see below).

Monitoring & Side Effects

• Blood Pressure: Watch for hypotension (especially if systolic < 90 mmHg).
• Heart Rate: Possible reflex tachycardia.
• Headache, Flushing, Dizziness: Common transient side effects.
• Pulmonary Edema: Rare, but risk increases with fluid overload or concurrent use of other tocolytics.

Contraindications

• Maternal Hypotension
• Severe Cardiac Disease
• Significant Hepatic Dysfunction
• Concurrent use with Magnesium Sulfate (risk of severe hypotension)

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2. Terbutaline (Bricanyl)

Mechanism of Action

• A beta-2 adrenergic receptor agonist that decreases intracellular calcium in uterine smooth muscle cells, reducing contractions.

Common Protocol

1. Loading Dose (IV Bolus)
   • Bricanyl 0.25 mg (½ amp of 0.5 mg/amp)
   • Give IV stat (single bolus)
2. Maintenance Infusion (IV Drip)
   • Bricanyl 2.5 mg (≈5 amps total)
   • Mix in 5% D/W 500 mL
   • Start infusion at 10 µg/min (approximately 30 drops/min; adjust per the institution’s IV set calibration)
   • Increase by 5 µg/min (≈15 drops/min) every 10 minutes
   • Maximum dose: 25 µg/min (≈75 drops/min) or until uterine contractions cease
3. Maintenance After Control of Contractions
   • Once contractions stop, continue the same infusion rate for another 2 hours
   • Then transition to subcutaneous (SC) terbutaline:
     • Bricanyl 0.25 mg SC every 4 hours for 6 doses
     • Overlap the first SC dose slightly with IV infusion to ensure continuous coverage
4. Alternate (Oral) Maintenance
   • Some protocols add Bricanyl 2.5–5 mg PO every 4–6 hours
   • Continue for 24–48 hours if contractions remain suppressed

Monitoring & Side Effects

• Heart Rate: Maternal pulse >140 bpm is a sign to reduce or discontinue infusion.
• Blood Pressure: Watch for hypotension.
• Pulmonary Edema: Increased risk if used >24–48 hours or with excessive IV fluids.
• Blood Glucose: May cause maternal hyperglycemia (and subsequent neonatal hypoglycemia).
• Electrolytes: Beta-agonists can cause hypokalemia, hyperlacticemia.

Contraindications

• Maternal Heart Disease (structural defects, ischemia, arrhythmias)
• Uncontrolled Hyperthyroidism
• Poorly Controlled Diabetes Mellitus
• Severe Hypertension
• Severe Hypovolemia
• Multiple Gestation or Polyhydramnios (heightened risk of fluid overload and side effects)

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Clinical Tips

1. 48-Hour Goal
   • Most tocolytics (nifedipine, terbutaline) aim to delay labor ≥48 hours—enough time for corticosteroid administration and/or maternal transfer to a tertiary care facility.
2. Fluid Management
   • Avoid excessive IV fluid to reduce risk of pulmonary edema, especially when using beta-agonists.
3. Combination Therapy
   • Concomitant magnesium sulfate and nifedipine can cause severe hypotension.
   • Generally avoid using multiple tocolytics simultaneously unless under direct specialist guidance.
4. Switching Agents
   • If nifedipine fails or is contraindicated (e.g., severe hypotension), terbutaline can be used (and vice versa).
   • Long-term oral therapy has limited proven benefit but may be used briefly in certain protocols.
5. Close Monitoring
   • Continuous maternal vital signs, fetal heart rate, contraction pattern, and possible cervical change should be documented.
   • Discontinue tocolytics if maternal or fetal contraindications arise or if preterm labor progresses despite maximum safe doses.

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Conclusion

Both nifedipine (Adalat) and terbutaline (Bricanyl) can be used to delay preterm birth, typically for up to 48 hours. This window allows for crucial interventions such as corticosteroid administration to enhance fetal lung maturity. When using these agents, strict monitoring is essential to promptly detect maternal cardiovascular compromise, pulmonary edema, or adverse fetal effects. If one agent fails or is contraindicated, the other can be considered, taking into account individual patient factors and institutional protocols.