Tocolytics are medications used to suppress premature uterine contractions and delay labor. Their main goal is to provide time for fetal lung maturation or maternal transfer to a higher-care facility.
Definition
Tocolytics are drugs that inhibit uterine contractions during preterm labor, thus delaying delivery for 24–48 hours.
Purpose
- Prevent or postpone preterm birth (<37 weeks)
- Allow antenatal corticosteroids to enhance fetal lung maturity
- Enable maternal stabilization or transport
Classification of Tocolytics
| Drug Class | Example(s) | Mechanism of Action |
|---|---|---|
| Beta-2 Adrenergic Agonists | Terbutaline, Ritodrine | Stimulate β₂ receptors → relax uterine smooth muscle |
| Calcium Channel Blockers | Nifedipine | Inhibit calcium influx → reduce uterine contractions |
| NSAIDs (Prostaglandin Inhibitors) | Indomethacin | Block prostaglandin synthesis → inhibit uterine activity |
| Oxytocin Antagonists | Atosiban | Block oxytocin receptor → prevent uterine contractions |
| Magnesium Sulfate | MgSO₄ | Competes with calcium at muscle binding sites → reduces contractility |
| Nitric Oxide Donors | Nitroglycerin | Relax smooth muscle by increasing cyclic GMP |
Terbutaline (Prototype Drug)
Brand Names: Brethine, Bricanyl
Class:
Pharmacologic (P): Beta-2 Adrenergic AgonistRoutes: PO, Subcutaneous (SQ), IV (in emergency settings)
Mechanism of Action (MOA)
Terbutaline stimulates β₂-adrenergic receptors in uterine smooth muscle → increases cyclic AMP → decreases intracellular calcium → causes relaxation of the uterus.
Result: Slows or halts premature labor contractions.
Uses
- Delay progression of preterm labor (usually up to 48 hours)
- Acute uterine relaxation during procedures (e.g., fetal distress or external version)
- Bronchospasm relief (since it’s also a bronchodilator)
Pharmacological Concept (Mnemonic)
“Terbutaline sounds like turbulence.”
Just like how turbulence slows down a plane, Terbutaline slows down labor by relaxing the uterus.
Plane = Uterus under contraction
Turbulence = Premature contractions
Terbutaline = Smooth flight (labor delay)
Adverse Effects (Mnemonic: PLANE)
| Letter | Effect | Explanation |
|---|---|---|
| P | ↓ Potassium | Causes hypokalemia |
| L | Low BP | Due to vasodilation |
| A | Arrhythmias | From cardiac β₁ stimulation |
| N | Nausea & Vomiting | From sympathetic activation |
| E | Elevated HR | Reflex tachycardia common |
Additional Adverse Effects
- Tremors and nervousness
- Headache and dizziness
- Pulmonary edema (rare, but serious)
- Hyperglycemia (especially in diabetic patients)
Drug Interactions
MAO Inhibitors (MAOIs): Risk of hypertensive crisisContraindications
- Hyperthyroidism
- Cardiac disorders (arrhythmia, ischemic heart disease)
- Diabetes mellitus (may worsen hyperglycemia)
- Hepatic or renal impairment
Precautions
- Continuous fetal and maternal monitoring required
- Avoid prolonged use (>48 hours) due to cardiovascular risks
- Discontinue if maternal HR >120 bpm or fetal distress observed
Nursing Considerations
| Aspect | Nursing Action |
|---|---|
| Before administration | Assess maternal HR, BP, and fetal HR baseline |
| During therapy | Monitor uterine activity and vital signs every 15 min |
| After administration | Observe for signs of pulmonary edema (dyspnea, crackles) |
| Education | Advise patient to avoid caffeine and stress; report palpitations or chest pain immediately |
| Storage | Keep in a cool, dry place away from light |
Comparison of Major Tocolytics
| Drug | Class | Duration of Action | Major Side Effect |
|---|---|---|---|
| Terbutaline | β₂-agonist | 2–4 hrs | Tachycardia, tremor |
| Nifedipine | Ca²⁺ channel blocker | 4–6 hrs | Hypotension, dizziness |
| Indomethacin | NSAID | 6–8 hrs | Ductus arteriosus closure (fetus) |
| Magnesium sulfate | Calcium antagonist | Continuous infusion | Respiratory depression |
| Atosiban | Oxytocin receptor antagonist | 6–8 hrs | Nausea, headache |
Clinical Pearl
Terbutaline is not recommended for long-term use in managing preterm labor because of maternal cardiovascular risks.
FDA advises hospital use only under supervision.
Mnemonic Recap
TURBULENCE AHEAD!
When a plane has turbulence (labor contractions), Terbutaline helps slow it down by relaxing the uterus.
Key Takeaways
- Tocolytics delay preterm labor, buying crucial time for fetal lung maturity.
- Terbutaline is a short-acting β₂-agonist that relaxes uterine muscles.
- Watch for tachycardia, hypotension, and hypokalemia.
- Avoid in cardiac, thyroid, or diabetic patients.
- Always ensure maternal-fetal monitoring during therapy.
FAQs About Tocolytics and Terbutaline
Q1. What is the main purpose of tocolytics?
To temporarily stop or delay premature uterine contractions to prevent preterm birth.
Q2. How does Terbutaline work as a tocolytic?
It activates β₂ receptors in the uterus, relaxing smooth muscle and stopping contractions.
Q3. Can Terbutaline be given orally?
Yes, but subcutaneous administration is preferred for rapid action in emergencies.
Q4. Why is Terbutaline use limited to 48 hours?
Prolonged use increases the risk of maternal cardiac complications.
Q5. What should nurses monitor during Terbutaline therapy?
Maternal HR, BP, fetal HR, uterine activity, and signs of pulmonary edema.
Q6. Which drug can reverse Terbutaline’s effect?
Beta-blockers (e.g., propranolol) can antagonize its uterine-relaxing effect.
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