What are the recommended dosing regimens of terbutaline for acute bronchospasm in adults and children and for tocolysis in pregnant women, and what are its contraindications and common adverse effects?

Terbutaline: Dosing, Indications, and Safety Profile

Acute Bronchospasm Management

For acute bronchospasm in adults, administer terbutaline 10 mg via nebulizer every 4-6 hours, or 0.25-0.5 mg subcutaneously, which provides effective bronchodilation within 5 minutes. 1, 2

Adult Dosing Regimens

Nebulized Administration:

• Standard dose: 10 mg nebulized, repeated every 4-6 hours if clinical improvement occurs 1
• For severe exacerbations with inadequate response, consider adding ipratropium bromide 500 µg to the nebulized terbutaline 1
• Drive the nebulizer with oxygen in acute severe asthma to simultaneously treat hypoxemia and bronchospasm 3

Subcutaneous Administration:

• Dose: 0.25 mg subcutaneously, repeated every 20 minutes for up to 3 doses 1
• Alternative dosing: 0.5 mg subcutaneously provides maximal bronchodilation with onset within 5 minutes 2
• This route is particularly effective when nebulized therapy is unavailable or poorly tolerated 1

Oral Maintenance:

• Start with 2.5 mg every 6-8 hours and adjust based on clinical response 2
• Oral terbutaline combined with aerosol administration represents a highly effective synergistic approach for maintenance therapy 2

Pediatric Dosing

For children with acute severe asthma, administer terbutaline 10 mg (or 0.3 mg/kg) nebulized, repeated every 1-4 hours if improvement occurs. 1

• If inadequate response after initial dose, repeat at 30 minutes after adding ipratropium bromide 250 µg (half the adult dose) 1
• Continue hourly nebulization for severe cases and consider hospital transfer 1

Tocolysis in Pregnancy

Terbutaline is classified as FDA Category C and TGA Category A for use in pregnancy, with evidence supporting its safety profile when used appropriately. 1

Acute Tocolysis Dosing

• Subcutaneous: 0.25 mg every 20 minutes for up to 3 doses for acute preterm labor 4
• After successful acute tocolysis, transition to oral maintenance: 20 mg/day divided into multiple doses 4
• Terbutaline provided more effective tocolysis with fewer adverse effects and better neonatal outcomes compared to salbutamol, with significantly higher gestational age at delivery and prolonged gestation 4

Continuous Subcutaneous Infusion

• Continuous subcutaneous terbutaline infusion after arrested preterm labor is associated with an extremely low incidence of serious adverse events (0.13% in a study of 9,359 patients) 5
• The most frequent serious adverse event was pulmonary edema (9 cases), with no maternal mortality 5
• Critical caveat: Patients with comorbidities and/or concomitant tocolysis with intravenous magnesium sulfate require close monitoring for serious adverse events 5

Important Pregnancy Considerations

• Systemic β2-agonists may have a tocolytic effect during delivery, potentially inhibiting uterine contractions 1
• Terbutaline is probably safe for breastfeeding 1
• SABAs (including terbutaline) are unlikely to cause structural anomalies, as observed risk in clinical studies is similar to the general population 1

Contraindications and Precautions

Absolute Contraindications

• Hypersensitivity to terbutaline or any component
• Patients at risk for cardiac arrhythmias (terbutaline may precipitate angina, particularly in elderly patients) 1

Critical Safety Warnings

Cardiovascular and Metabolic Effects:

• Systemic administration causes cardiovascular adverse effects including maternal and fetal tachycardia, maternal hyperglycemia, and neonatal hypoglycemia 1
• First treatment should be supervised in elderly patients due to risk of angina 1
• Monitor for tachycardia, myocardial irritability, and increased myocardial oxygen demand 1

Respiratory Considerations:

• In COPD patients with CO2 retention and acidosis, drive nebulizers with compressed air, NOT oxygen, to prevent worsening hypercapnia 6, 3
• Oxygen can be administered simultaneously via nasal cannula at 1-2 L/min if needed 6

Common Adverse Effects

Most Frequent Side Effects:

• Tachycardia (dose-dependent and more common than with salbutamol) 4
• Tremor (dose-dependent) 2
• Anxiety (significantly more common than salbutamol) 4
• Palpitations 2
• Maternal hyperglycemia (in pregnancy) 1
• Neonatal hypoglycemia (when used near term) 1

The incidence of side effects is clearly dose-dependent, supporting the recommendation to start with lower doses and titrate based on clinical response. 2

Clinical Decision Algorithm

For Acute Bronchospasm:

1. Assess severity: respiratory rate >25/min, heart rate >110/min, peak flow <50% predicted indicates severe exacerbation 1
2. Start with nebulized terbutaline 10 mg every 4-6 hours 1
3. If inadequate response after first dose, add ipratropium 500 µg and continue combination every 4-6 hours 1
4. For patients unable to use nebulizer, give 0.25 mg subcutaneously, repeat every 20 minutes up to 3 doses 1
5. Transition to oral maintenance (2.5 mg every 6-8 hours) once stabilized 2

For Tocolysis:

1. Acute preterm labor: 0.25 mg subcutaneously every 20 minutes for up to 3 doses 4
2. After successful acute tocolysis, transition to oral 20 mg/day divided doses 4
3. Critical: Avoid concomitant magnesium sulfate when possible; if necessary, monitor closely for pulmonary edema 5
4. Monitor maternal pulse, blood glucose, and fetal heart rate 1

Important Clinical Pitfalls

• Excessive use should be avoided in pregnancy due to cumulative cardiovascular and metabolic effects 1
• Oral terbutaline after successful parenteral tocolysis does NOT reduce preterm birth rates when initiated at 24-34 weeks' gestation, though post-hoc analysis suggests benefit when started before 32 weeks 7
• Neonates exposed to terbutaline at term or during lactation should be observed for tachycardia, irritability, and hypoglycemia 1
• There is no evidence that subcutaneous terbutaline has advantages over inhaled β2-agonists for acute bronchospasm 1