Terbutaline
Terbutaline sulfate
Also known as: Brethine · Bricanyl · Monovent · KWD-2019 · terbutaline sulphate · terbutalini sulfas · Terbutaline sulfate · Terbutalinum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceBradyarrhythmias (extra-label)
- q8-12h
NA
Governing clinical context (2)
- 1. Do not confuse mg/kg dosages with mg/dog or mg/cat.
- 2. Terbutaline should not be administered as an IV bolus; administer slowly if IV use cannot be avoided.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Terbutaline is a synthetic, selective beta-2 adrenergic agonist primarily used in veterinary medicine as a bronchodilator. It is frequently prescribed for the adjunctive management of cardiopulmonary diseases such as feline asthma, canine chronic bronchitis, collapsing trachea, and pulmonary edema.
Beyond its respiratory applications, terbutaline is occasionally utilized off-label as a tocolytic agent to inhibit premature labor by relaxing uterine smooth muscle, and as a chronotropic agent to manage certain bradyarrhythmias. In equine medicine, it has diagnostic utility for quantifying anhidrosis via intradermal injection.
Clinical Pearl: While highly selective for beta-2 receptors at standard doses, higher doses can cause beta-1 spillover, leading to direct cardiac stimulation. Reflex tachycardia secondary to peripheral vasodilation is also a common clinical observation.
Mechanism of action
Terbutaline selectively binds to and stimulates beta-2 adrenergic receptors located predominantly in bronchial, vascular, and uterine smooth muscle.
Mechanism Pathway: Beta-2 receptor activation → Stimulation of adenylyl cyclase → Increased intracellular cyclic AMP (cAMP) → Activation of protein kinase A (PKA) → Decreased intracellular calcium concentrations → Smooth muscle relaxation.
This results in significant bronchodilation and reduced airway resistance. At therapeutic doses, it has minimal affinity for beta-1 receptors (cardiac muscle) and virtually no alpha-adrenergic activity.
Safety & warnings
Contraindications
- Heart disease (especially congestive heart failure or cardiomyopathy)
- Known hypersensitivity to terbutaline or sympathomimetic amines
- Severe cardiac arrhythmias
- Hypertrophic cardiomyopathy (relative contraindication)
Adverse effects
- Increased heart rate (tachycardia)
- CNS excitement (nervousness)
- Dizziness
- Sweating (reported in horses after parenteral injection)
- Transient hypokalemia
- Muscle tremors
- Restlessness or excitement
- Hypokalemia (with high doses or prolonged use)
- Hypertension or hypotension
Precautions
Use with extreme caution in patients with diabetes mellitus, hyperthyroidism, hypertension, seizure disorders, or cardiac disease (especially with concurrent arrhythmias).
Note: Terbutaline can cause transient hypokalemia. If an animal is susceptible to developing hypokalemia, additional serum potassium monitoring should be performed early in therapy.
Drug interactions
May predispose the patient to ventricular arrhythmias, particularly with preexisting cardiac disease; use cautiously.
May antagonize the bronchodilating and cardiovascular actions of terbutaline.
Concurrent use with digitalis glycosides may increase the risk of cardiac arrhythmias.
May potentiate the vascular effects of terbutaline.
May increase the risk of developing adverse cardiovascular effects.
May potentiate the vascular effects of terbutaline.
Antagonize the bronchodilating effects of terbutaline
Additive cardiovascular toxicity and CNS stimulation
Sensitize the myocardium, increasing the risk of severe arrhythmias
May potentiate vascular effects
Monitoring
- Clinical symptom improvement (respiratory rate/effort)
- Auscultation of lung sounds
- Cardiac rate and rhythm (especially if indicated for arrhythmias or if tachycardia develops)
- Serum potassium (early in therapy if the animal is susceptible to hypokalemia)
- Heart rate and rhythm
- Respiratory rate and effort
- Serum potassium levels (with prolonged or high-dose therapy)
Pharmacokinetics
Half-life
Absorption
In humans, 33-50% of an oral dose is absorbed. Well-absorbed following SC administration (onset within 15 mins, peak 30-60 mins). In horses, oral bioavailability is very poor (<1%).
Distribution
Distributed into milk at levels approximately 1% of the oral dose given to the mother.
Metabolism
Metabolized in the liver to an inactive sulfate conjugate.
Elimination
Principally excreted unchanged in the urine (60%).
Overdose
Clinical signs of significant systemic overdose may include arrhythmias (bradycardia, tachycardia, heart block, extrasystoles), hypertension, fever, vomiting, mydriasis, and CNS stimulation.
Treatment:
- For recent oral ingestion without significant cardiac/CNS effects: Empty gut, administer activated charcoal, and a cathartic.
- For severe cardiac arrhythmias: A beta-blocking agent (e.g., propranolol) can be used, but caution is advised as it may precipitate severe bronchoconstriction.
Available products
Formulations
- Injection
- Injectable: 0.5 mg/ml solution
- Oral: 5 mg tablets
- Oral: 1.5 mg/5 ml syrup
Human-labeled
- Terbutaline Sulfate Tablets: 2.5 mg & 5 mg (Brethine®, generic)
- Terbutaline Injection: 1 mg/mL in 1 mL vials & 2 mL amps with 1 mL fill (Brethine®, generic)
- Bricanyl 0.5 mg/ml injection
- Bricanyl 5 mg tablets
- Bricanyl 1.5 mg/5 ml syrup
- Monovent
Regulatory status
Approved for human use; used off-label in veterinary medicine under the cascade.
Prescription Only Medicine (POM). Human products (Bricanyl, Monovent) used under the prescribing cascade.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets should be stored in tight containers at room temperature (15-30°C). Injection should be stored at room temperature (15-30°C) and protected from light. Injection is stable over a pH range of 1-7; discolored solutions should not be used.
Client information
- Purpose: Terbutaline is used to open up the airways in the lungs, making it easier for your pet to breathe.
- Administration: Give exactly as prescribed by your veterinarian. Do not stop the medication abruptly unless instructed.
- Side Effects: You may notice your pet's heart beating faster than normal, mild tremors, or jitteriness/nervousness. These effects are usually mild and temporary.
- When to Call the Vet: Contact your veterinarian immediately if your pet's breathing worsens, if they collapse, or if they become acutely ill.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.