What are the recommended pediatric dosing guidelines for terbutaline (including oral, inhaled, and intravenous routes) for children aged ≥2 months?

Terbutaline Dosing in Pediatric Patients

For acute severe asthma in children aged ≥2 months, administer terbutaline 10 mg (or 0.3 mg/kg) via nebulizer, or 2.5 mg subcutaneously if the inhaled route is unavailable, with intravenous terbutaline reserved for PICU patients who fail maximal conventional therapy at doses of 2-4.5 mcg/kg/hour continuous infusion after a loading dose of 2 mcg/kg over 5 minutes. 1

Nebulized Terbutaline Dosing

Standard nebulized dose:

• 10 mg via nebulizer for children with acute severe asthma 1
• Weight-based alternative: 0.3 mg/kg via nebulizer 1
• Administer via metered-dose inhaler (MDI) with spacer if nebulizer unavailable: 250 mcg per actuation, repeat up to 20 times 1

The British Thoracic Society guidelines establish these doses for children presenting with severe asthma features (respiratory rate >50/min, pulse >140/min, use of accessory muscles, or peak flow <50% predicted). 1 Nebulized therapy should be delivered with high-flow humidified oxygen as the driving gas. 1

Subcutaneous Terbutaline Dosing

Subcutaneous dose: 2.5 mg when the inhaled route is unavailable 1

This route is specifically indicated when nebulizers or MDI with spacer cannot be used, though inhaled delivery remains the preferred first-line approach. 1 The subcutaneous route provides rapid onset within 5 minutes but should not replace inhaled therapy when feasible. 2

Intravenous Terbutaline Dosing

For PICU patients with life-threatening asthma:

Loading Dose

• 2 mcg/kg IV over 5 minutes (range: 0.9-2 mcg/kg) 3, 4
• Single doses of 10-30 mcg/kg over 5 minutes have been studied and found safe, though lower loading doses are typically sufficient 4

Continuous Infusion

• Initial rate: 2.4-4.5 mcg/kg/hour 3
• Therapeutic range: 1-5 mcg/kg/hour, titrated to clinical response 5
• Maximum bronchodilation typically achieved at plasma levels around 30 nmol/L (range 20-60 nmol/L) 3

The dose-response relationship is linear, with optimal bronchodilation occurring at maintenance infusion rates of approximately 4.5 mcg/kg/hour. 3 Research demonstrates that a loading dose of 2 mcg/kg followed by 4.5 mcg/kg/hour continuous infusion is suitable for severe bronchoconstriction in children. 3

Important consideration: Terbutaline elimination may be more rapid in acutely ill asthmatic children in the PICU compared to stable patients, supporting the use of continuous infusion rather than intermittent boluses. 4

Age-Specific Considerations

• Infants 6 months to 2 years: IV terbutaline has been studied and found safe in this age group, though pharmacokinetic parameters (half-life, volume of distribution) correlate with age 4
• Children 2-16 years: Standard dosing applies across this age range with dose adjustment based on clinical response 4, 3

Younger children may have different pharmacokinetic profiles, with statistically significant correlations between age and elimination half-life (r=0.4, P<0.006) and volume of distribution (r=0.33, P<0.02). 4

Monitoring Requirements

Cardiovascular monitoring is essential:

• Expect heart rate increase of approximately 20-32 bpm 3, 6
• Systolic blood pressure typically rises 10-15 mmHg 3
• Diastolic blood pressure typically falls 10-15 mmHg 3
• Continuous cardiac monitoring recommended for IV therapy 5

Laboratory monitoring:

• Serum potassium levels (hypokalaemia occurs in approximately 13% of patients) 5
• No routine cardiac enzyme monitoring needed unless clinical concern arises 6

Common side effects include headache and tremor in all patients receiving therapeutic plasma levels, though these are dose-dependent and generally well-tolerated. 3

Clinical Decision Algorithm

1. First-line: Nebulized terbutaline 10 mg (or 0.3 mg/kg) with oxygen as driving gas 1
2. If nebulizer unavailable: MDI with spacer, 250 mcg per actuation up to 20 times 1
3. If inhaled route fails/unavailable: Subcutaneous 2.5 mg 1
4. If maximal conventional therapy fails in PICU: IV loading dose 2 mcg/kg over 5 minutes, then continuous infusion starting at 2.4-4.5 mcg/kg/hour 3
5. Titrate IV infusion based on clinical response and side effects, with dose adjustments evaluated at regular intervals 3

Critical Safety Considerations

Contraindications to escalation:

• Four patients in one cohort required inotropic support during IV terbutaline therapy, though all improved without requiring mechanical ventilation 5
• No cardiac arrhythmias or mortality occurred in a cohort of 77 children receiving IV terbutaline at 1-5 mcg/kg/min 5
• Continuous nebulization (16 mg over 8 hours) produces similar plasma concentrations and cardiovascular effects as intermittent dosing (4 mg every 2 hours × 4 doses) 6

Key pitfall: Do not use terbutaline as first-line therapy when standard inhaled beta-agonists (salbutamol/albuterol) are available, as terbutaline is typically reserved for refractory cases or when other agents are unavailable. 1 The guideline evidence positions terbutaline as an alternative when the inhaled route is unavailable, not as a preferred agent. 1