Tocolytics

High-yield Verified · Oct 2026

Prototype: terbutaline

Tocolytics are a class of medications used for terbutaline.

Medical view → mechanisms, drug comparisons and Step 1 pharmacology

Buy time, not term. Each tocolytic’s hazard comes from what else it does — the heart with terbutaline, blood pressure with nifedipine, the fetal ductus with indomethacin.

How it works in the body

The system involved, what goes wrong, and how the drug and body interact.

01 What tocolysis is for

Tocolysis delays delivery in women with preterm contractions. It is intended to prolong gestation for two to seven days — not to reach term — to allow transfer to a higher-level facility, a course of antenatal corticosteroids for fetal lung maturity, and group B streptococcus prophylaxis. It is beneficial in preterm labor before 34 weeks, but tocolytics are not recommended as prophylaxis.

There are no FDA-approved medications for tocolysis; all are used off-label. Myometrial contraction, like that of all smooth muscle, is calcium-mediated: calcium enters through voltage-gated channels, binds calmodulin, and activates myosin light chain kinase. Each class quiets the myometrium by a different mechanism. Magnesium sulfate is covered on its own page.

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Each tocolytic class quiets myometrial contraction by a different mechanism.

02 Terbutaline: a bronchodilator with a tocolysis box

Terbutaline is a β-adrenergic agonist labeled only for bronchospasm. It stimulates adenyl cyclase, raising cAMP, which relaxes smooth muscle. Its labels carry a boxed warning: the injection has not been approved and should not be used for prolonged tocolysis (beyond 48 to 72 hours), the oral tablets should not be used for acute or maintenance tocolysis, and neither should be used for maintenance tocolysis at home.

The box cites serious adverse reactions in the mother, including deaths: increased heart rate, transient hyperglycemia, hypokalemia, cardiac arrhythmias, pulmonary edema and myocardial ischemia. The fetus can develop an increased heart rate, and the newborn hypoglycemia. Terbutaline crosses the placenta.

03 Nifedipine and indomethacin

Nifedipine, a calcium channel blocker, inhibits calcium entry into uterine smooth muscle and is the most common agent in its class for tocolysis (off-label; see the Calcium channel blockers page). Its maternal risks include flushing, headache, dizziness, nausea and hypotension, and it is used with great caution in women with hypotension or cardiac conditions.

Indomethacin, a non-selective COX inhibitor, reduces prostaglandin production and is the most common NSAID used (off-label; see the NSAIDs page). Its key obstetric hazard is fetal: NSAIDs at about 30 weeks and later increase the risk of premature closure of the fetal ductus arteriosus, and from about 20 weeks they can cause fetal renal dysfunction leading to oligohydramnios. Its label carries the NSAID boxed warning for cardiovascular thrombotic and gastrointestinal events.

Drug names

Generic Brand

terbutaline —

nifedipine —

indomethacin —

Indications

Terbutaline — labeled only for prevention and reversal of bronchospasm in patients 12 years and older; it is not approved for tocolysis and is boxed against prolonged (injection) or any oral tocolysis
Nifedipine — labeled for vasospastic and chronic stable angina; used off-label as a tocolytic
Indomethacin — labeled for rheumatoid arthritis, ankylosing spondylitis, osteoarthritis, acute painful shoulder and acute gouty arthritis; used off-label as a tocolytic

Mechanism of action

Terbutaline stimulates β2-adrenergic receptors, activating adenyl cyclase and raising cAMP, which relaxes smooth muscle. Nifedipine inhibits calcium entry into uterine smooth muscle, so calcium–calmodulin cannot activate myosin light chain kinase. Indomethacin inhibits cyclooxygenase, reducing prostaglandin production from arachidonic acid.

In plain terms

Uterine muscle needs calcium to contract. These drugs either keep calcium out, push the muscle cell toward relaxing, or cut the prostaglandin signals that drive contractions — for long enough to give steroids and move the mother.

Therapeutic effects — what you'll see working

Success is a short delay in delivery — typically 48 hours — long enough for antenatal corticosteroids and transfer, without maternal cardiopulmonary or fetal harm.

Short-term delay of preterm delivery Uterine relaxation

Short-term delay of preterm delivery: Tocolysis is intended to prolong gestation for two to seven days, creating a window for antenatal corticosteroids, transfer and GBS prophylaxis.
Uterine relaxation: β2 stimulation raises cAMP; calcium channel blockade removes the calcium that activates myosin light chain kinase; COX inhibition lowers prostaglandins.

Adverse effects

The hazards are maternal-cardiopulmonary with terbutaline, hemodynamic with nifedipine, and fetal with indomethacin.

■ Boxed warning · terbutaline (injection and tablets) Report immediately

Terbutaline has not been approved and should not be used for prolonged tocolysis beyond 48 to 72 hours (injection) or for acute or maintenance tocolysis (oral), and never for maintenance tocolysis at home.

Serious adverse reactions, including death, have been reported in pregnant women: increased heart rate, transient hyperglycemia, hypokalemia, cardiac arrhythmias, pulmonary edema and myocardial ischemia. Increased fetal heart rate and neonatal hypoglycemia may occur.

■ Boxed warning · Indocin (indomethacin) Hold & notify

NSAIDs increase the risk of serious cardiovascular thrombotic events and of gastrointestinal bleeding, ulceration and perforation, which can be fatal.

Indomethacin is contraindicated in the setting of CABG surgery.

Fetal ductus arteriosus and oligohydramnios (indomethacin) Hold & notify

NSAIDs at about 30 weeks of gestation and later increase the risk of premature closure of the fetal ductus arteriosus; from about 20 weeks they can cause fetal renal dysfunction and oligohydramnios.

The label says to avoid NSAIDs at about 30 weeks and later, to limit dose and duration between about 20 and 30 weeks, and to consider ultrasound monitoring of amniotic fluid if treatment extends beyond 48 hours; discontinue if oligohydramnios occurs.

Tachycardia, arrhythmia and pulmonary edema (terbutaline) Hold & notify

β-agonists can raise pulse and blood pressure and produce ECG changes; terbutaline is used with caution in cardiovascular disorders, hyperthyroidism and diabetes.

β-agonists may cause significant, usually transient hypokalemia, and large IV doses have aggravated diabetes and ketoacidosis.

Hypotension (nifedipine) Hold & notify

Occasional patients have had excessive and poorly tolerated hypotension, usually during initial titration or dose increases.

Maternal flushing, headache, dizziness and nausea are also reported with tocolytic use.

Interactions

Terbutaline + other sympathomimetics drug

Combined cardiovascular effects may be deleterious — not recommended.

Terbutaline + β-blockers drug

β-blockers block terbutaline’s effect and may cause severe bronchospasm in asthma.

Terbutaline + loop or thiazide diuretics drug

Hypokalemia and ECG changes may be acutely worsened.

Terbutaline + MAO inhibitors or tricyclic antidepressants drug

Vascular effects may be potentiated — extreme caution.

Nifedipine + CYP3A4 inducers (phenytoin) or grapefruit juice drug

Inducers lower nifedipine exposure; grapefruit about doubles it.

Contraindications

Terbutaline’s label contraindicates the very use that tempts clinicians — prolonged or oral tocolysis. Indomethacin’s fetal warnings set a gestational-age limit.

Terbutaline injection — prolonged tocolysis beyond 48–72 hours, or maintenance tocolysis at home

Labeled contraindication and boxed warning — serious maternal cardiopulmonary reactions and deaths.

Terbutaline tablets — acute or maintenance tocolysis

Labeled contraindication and boxed warning.

Terbutaline — hypersensitivity to sympathomimetic amines

Labeled contraindication.

Indomethacin — aspirin or NSAID hypersensitivity (asthma, urticaria), known hypersensitivity, or CABG surgery

Labeled contraindications.

Indomethacin — pregnancy at about 30 weeks of gestation or later use caution

Avoid: risk of premature closure of the fetal ductus arteriosus.

Terbutaline — cardiovascular disorders (ischemic heart disease, arrhythmias, hypertension), hyperthyroidism, diabetes, seizure disorders use caution

Use with caution: sympathomimetic cardiovascular and metabolic effects.

Nifedipine — maternal hypotension or cardiac conditions use caution

Use with great caution in tocolysis because of hypotension.

When to hold

Assess before giving — these findings mean hold the dose and act.

Maternal tachycardia, chest pain, arrhythmia or dyspnea on terbutaline

Stop and notify — signs of myocardial ischemia, arrhythmia or pulmonary edema.

Maternal hypotension or dizziness on nifedipine

Hold and notify the provider.

Oligohydramnios on ultrasound during indomethacin

Discontinue indomethacin and notify — fetal renal dysfunction.

Labs & levels

Test Therapeutic / normal Toxic / critical

Maternal heart rate, blood pressure and fetal heart rate Throughout tocolysis — —

Blood glucose and potassium (terbutaline) During therapy; monitor the newborn for hypoglycemia — —

Amniotic fluid by ultrasound (indomethacin) Consider if NSAID treatment extends beyond 48 hours — —

Nursing considerations

The RN-specific layer — each action paired with the reason it matters.

During tocolysis

Monitor maternal heart rate, blood pressure, breath sounds and fetal heart rate, and report chest pain or dyspnea.

Why: Terbutaline can cause tachycardia, arrhythmias, myocardial ischemia and pulmonary edema; nifedipine can cause hypotension.

Check blood glucose and potassium during terbutaline, and alert the neonatal team to watch the newborn’s glucose.

Why: Terbutaline causes transient hyperglycemia and hypokalemia; neonatal hypoglycemia may follow maternal use.

Make sure terbutaline is not continued beyond 48 to 72 hours or sent home for maintenance, and that oral terbutaline is not used for tocolysis.

Why: The boxed warning: prolonged, oral or home tocolysis has caused serious harm and death.

Coordinating care

Confirm gestational age before indomethacin, and anticipate amniotic fluid monitoring if it continues beyond 48 hours.

Why: NSAIDs at about 30 weeks and later risk premature ductal closure; oligohydramnios can occur from about 20 weeks.

Coordinate antenatal corticosteroids, transfer and notification of the high-risk obstetric, neonatal and anesthesia teams.

Why: Tocolysis exists to buy time for these interventions.

Common questions

What are Tocolytics used for?

Terbutaline for labeled only for prevention and reversal of bronchospasm in patients 12 years and older. Nifedipine for labeled for vasospastic and chronic stable angina. Indomethacin for labeled for rheumatoid arthritis, ankylosing spondylitis, osteoarthritis, and acute painful shoulder and acute gouty arthritis.

How do Tocolytics work?

What are the serious side effects of Tocolytics?

Watch for terbutaline has not been approved and should not be used for prolonged tocolysis beyond 48 to 72 hours (injection) or for acute or maintenance tocolysis (oral), and never for maintenance tocolysis at home; (with indomethacin) NSAIDs increase the risk of serious cardiovascular thrombotic events and of gastrointestinal bleeding, ulceration and perforation, which can be fatal; (with indomethacin) NSAIDs at about 30 weeks of gestation and later increase the risk of premature closure of the fetal ductus arteriosus; from about 20 weeks they can cause fetal renal dysfunction and oligohydramnios.

When should a nurse hold Tocolytics, and what safety checks apply?

Maternal tachycardia, chest pain, arrhythmia or dyspnea on terbutaline: stop and notify — signs of myocardial ischemia, arrhythmia or pulmonary edema. Maternal hypotension or dizziness on nifedipine: hold and notify the provider. Oligohydramnios on ultrasound during indomethacin: discontinue indomethacin and notify — fetal renal dysfunction.

What labs should be monitored with Tocolytics?

Monitor maternal heart rate, blood pressure and fetal heart rate, blood glucose and potassium (terbutaline), and amniotic fluid by ultrasound (indomethacin).

Sources

Reviewed by Hae Suk Lee, RN

Educational summary for nursing students. Always verify against current prescribing information and your institution's protocols before administering. Not medical advice.