Terbutaline: A Parenteral Bronchodilator
Terbutaline is a selective beta-2 adrenergic agonist that can be administered subcutaneously for severe bronchospasm. While nebulized albuterol is the standard first-line treatment for acute asthma, some patients present with bronchospasm so severe that they cannot generate enough airflow to effectively inhale nebulized medications. In these cases, subcutaneous terbutaline provides an alternative route to deliver bronchodilator therapy.
Mechanism of Action
Like albuterol, terbutaline stimulates beta-2 adrenergic receptors on bronchial smooth muscle, causing relaxation and bronchodilation. When administered subcutaneously, it bypasses the need for adequate inspiratory flow, making it effective even in patients with near-complete airway obstruction who cannot benefit from inhaled medications.
Indications for Subcutaneous Terbutaline
- Severe asthma exacerbation not responding to nebulized bronchodilators
- Status asthmaticus with inadequate air movement for effective nebulization
- Severe bronchospasm in patients who cannot cooperate with nebulizer treatment (young children, cognitively impaired patients)
- Situations where nebulization is impractical (extrication, confined spaces)
Dosing
- Adult: 0.25 mg (0.25 mL of the 1 mg/mL concentration) subcutaneously. May repeat once in 15 to 30 minutes if needed.
- Pediatric: 0.01 mg/kg subcutaneously (maximum 0.25 mg per dose)
- Onset: 5 to 15 minutes subcutaneously
- Duration: 1.5 to 4 hours
Side Effects and Monitoring
Because terbutaline has some beta-1 activity (especially at higher doses), patients may experience tachycardia, palpitations, tremor, nervousness, and hypokalemia. Monitor heart rate and rhythm continuously after administration. Use caution in patients with known cardiac disease, hypertension, or hyperthyroidism. Document the indication, dose, site of injection, time of administration, and the patient's respiratory and hemodynamic response.
Clinical Context
Some EMS systems have replaced terbutaline with IM or IV epinephrine for severe bronchospasm. However, terbutaline has a more favorable beta-2 selectivity profile, meaning less cardiac stimulation at bronchodilator doses. Know your local protocols and understand the rationale for whichever parenteral bronchodilator your system carries. For the NREMT exam, understand the concept of subcutaneous bronchodilator delivery as an alternative to the inhaled route when the patient cannot effectively inhale medications.