Terbutaline

Terbutaline is a beta2-adrenergic agonist used mainly for relief of reversible bronchoconstriction. Veterinary applications include feline asthma and selected canine or equine airway disorders with a bronchospastic component. Injectable preparations provide an option for selected acute episodes, while oral use and clinical response differ substantially among species.

Group

Beta2-adrenergic bronchodilator

Mechanism of Action

Terbutaline activates beta2 receptors coupled to stimulatory G proteins, increasing adenylyl cyclase activity and cyclic AMP. Downstream signaling reduces airway smooth-muscle contraction and produces bronchodilation. Additional beta-adrenergic effects can influence cellular potassium uptake and smooth muscle at other sites. Its primary respiratory effect is relaxation of bronchial muscle rather than suppression of the underlying airway inflammation.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Bronchoconstriction	1.25–5 mg/animal	PO	Every 8 h
Acute bronchoconstriction	3–5 mcg/kg	SC	Every 4–6 h	Usually one emergency dose; repeat only if necessary.
Tracheal collapse or expiratory dyspnea	1.25–5 mg/animal	PO	Every 8–12 h
Bradyarrhythmia adjunct	0.2 mg/kg	PO	Every 8–12 h	Benefit often partial or temporary.
Premature labor suppression	0.03 mg/kg	PO, SC	Every 8 h	Stop 48 hours before calculated delivery date to permit normal labor.
Acute tracheal collapse bronchodilation	0.01 mg/kg	IV, IM, SC

Cats

Use / stage	Dose	Route	Schedule	Instructions
Bronchoconstriction	0.1 mg/kg	PO	Every 8 h
Bronchoconstriction	0.625 mg/animal	PO	Every 12 h
Acute bronchoconstriction	5–10 mcg/kg	SC, IM	Every 4 h
Acute bronchoconstriction	0.05 mg/animal	SC		Common fixed feline amount.
Acute bronchoconstriction	0.01 mg/kg	IV, SC, IM
Feline asthma maintenance	0.312–0.625 mg/animal	PO	Every 8–12 h	Larger cats have received up to 1.25 mg; titrate to effect.
Bradyarrhythmia adjunct	0.625 mg/animal	PO	Every 8–12 h

Horses

Use / stage	Dose	Route	Schedule	Instructions
Equine asthma bronchoconstriction	2–5 mcg/kg	IV	Every 6–8 h	Or as needed; oral absorption is poor.
Reported terbutaline therapy	0.0033 mg/kg	IV

Indications

Relief of acute bronchospasm in cats with asthma.
Adjunctive bronchodilation in selected cats or dogs with reversible airway obstruction associated with asthma or bronchitis.
Short-term relief of bronchoconstriction in selected horses with equine asthma using a supported parenteral regimen.

Contraindications

Cardiac disease or tachyarrhythmia risk
Late gestation unless suppression of uterine contractions is intended

Interactions

Other cardiac stimulants increase adverse effects.

Adverse effects

Tachycardia, tremor, arrhythmias, hypokalemia and hyperglycemia.

Toxicity

Excess beta stimulation can cause marked hypokalemia; potassium replacement must be controlled by measured concentrations and ECG. Excess beta stimulation can cause arrhythmias, tremor, hyperthermia and electrolyte shifts. ECG and potassium monitoring guide treatment; beta blockade may worsen bronchoconstriction.

Preparations

Preparation	Form	Strength	Route
Terbutaline 2.5 mg	Tablet	2.5 mg / tablet	PO
Terbutaline 5 mg	Tablet	5 mg / tablet	PO
Terbutaline sulfate injection 1 mg/mL	Injection	1 mg / mL	SC, IM, IV

Monitoring and Administration

Monitor pulse and potassium with high exposure. Oxygen and anti-inflammatory treatment may also be needed during bronchospasm.

Discard darkened injection; reported syrup suspensions remained stable for 55 days.

Size-based canine chronic-airway alternatives give 0.625-1.25 mg small, 1.25-2.5 mg medium, or 2.5-5 mg large dogs every 12 hours without numerical size boundaries. Equine quantitative intradermal sweat testing uses serial dilution and local response measurements; intradermal route is not a systemic bronchodilator dose.