Bronchodilator · Beta-2 agonist · Tocolytic

Terbutaline (Brethine)

Also called Brethine, Bricanyl

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Indications

• Prevention and reversal of bronchospasm from asthma, bronchitis or emphysema, by SC injection at age 12 and up (label)
• Severe asthma when inhaled drug cannot get in; IV infusion is off-label in the US and not routine in adults
• Uterine tachysystole with a worrying tracing after oxytocin is stopped, 0.25 mg SC (off-label)
• Tocolysis for up to 48 h to allow steroids (off-label; boxed warning beyond 48–72 h)
• Vasopressor extravasation when phentolamine is unavailable, infiltrated locally (off-label)

Dosing

Mechanism of action

Terbutaline is a selective β₂-adrenergic agonist. The β₂ receptor couples to Gs, so adenylyl cyclase raises cAMP and protein kinase A phosphorylates targets that lower intracellular calcium, inhibit myosin light-chain kinase and open large-conductance K⁺ channels, relaxing bronchial, uterine and vascular smooth muscle. The same pathway stimulates Na⁺/K⁺-ATPase, which drives potassium into cells, and increases glycogenolysis. Selectivity is relative: at higher doses β₁ stimulation adds tachycardia.

Pharmacology

• Respiratory: bronchodilation within 15 min of a SC dose; less mast cell mediator release
• Cardiovascular: tachycardia from vasodilation and, at higher doses, β₁ stimulation; palpitations, arrhythmias, myocardial ischemia
• Metabolic: hypokalemia, hyperglycemia and lactic acidosis, which can mimic worsening asthma
• Uterine: relaxes the myometrium, the basis of short-term tocolysis
• Neuromuscular: tremor
• Fetal and neonatal: crosses the placenta, causing fetal tachycardia and newborn hypoglycemia

Pharmacokinetics

Chemistry

• (±)-5-[2-(tert-butylamino)-1-hydroxyethyl]benzene-1,3-diol as the sulfate salt (2:1), MW 548.65 (label)
• The resorcinol ring escapes COMT and the tert-butyl group on the amine favors β₂ receptors, giving a longer, more selective action than isoproterenol
• Racemic; the R-enantiomer carries the β₂ activity
• Hydrophilic amine, pKa about 8.7 (PubChem), mostly ionized at pH 7.4
• 1 mg/mL in sodium chloride, pH 3–5; protect from light and discard if discolored (label)

Adverse effects and cautions

In the one-pagers

• Asthma and COPD ExacerbationsBronchodilators, steroids, magnesium and parenteral β-agonists: Epinephrine or terbutaline: 0.3–0.5 mg or 0.25 mg SC every 20 min ×3: When inhaled drug cannot get in
• Vasopressors and InotropesLines, extravasation and titration: Extravasation: stop the infusion, aspirate, remove the catheter, mark and elevate. For catecholamines or phenylephrine, infiltrate phentolamine 5–10 mg in 10–15 mL saline subcutaneously as soon as possible (label: within 12 h). Alternatives: terbutaline or topical nitroglycerin.
• Obstetric EmergenciesDrugs in pregnancy in the ICU: Betamethasone (12 mg IM, two doses 24 h apart) for likely delivery before 34 weeks raises glucose and WBC for days, mimicking infection. Magnesium before 32 weeks cut moderate or severe cerebral palsy from 3.5% to 1.9%, a secondary outcome (BEAM, Rouse 2008). Rho(D) immune globulin 300 mcg covers 30 mL of fetal whole blood. Terbutaline carries an FDA boxed warning ag

Other bronchodilator drugs

• Albuterol

Sources

1. FDA label: Terbutaline Sulfate Injection (Fresenius Kabi, 2022)
2. UK SmPC: Bricanyl Injection (2022)
3. FDA safety communication on terbutaline for preterm labor (2011)
4. PubChem: terbutaline

For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow your local protocols and medical direction.