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Terbutaline Sulfate (Brethine)
Revised: October 04, 2022
Published: September 12, 2011

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand Name: Brethine

Available as 2.5 mg tablets, 5 mg tablets, injectable, and as a metered-dose inhaler


Terbutaline is a type of drug called a beta-2 agonist. It is important to understand a bit about the autonomic nervous system, which is part of the nervous system involved in the body's automatic functions such as heart rate control, changes in circulation, dilation and constriction of pupils, etc. The autonomic nervous system is divided into two parts: the sympathetic nervous system, which prepares the body for fight or flight situations; and the parasympathetic nervous system, which maintains the body's status quo.

Nerves of the sympathetic nervous system are activated by stimulation of receptors called alpha and beta receptors. These receptors are further classified into alpha1, alpha2, beta1, beta2, and even beta3 receptors. The beta2 receptor is the relevant one for terbutaline sulfate.

When a fight or flight situation occurs, adrenaline (also called epinephrine) and its associated neurotransmitter norepinephrine are released, leading to the stimulation of all the alpha and beta receptors. The beta2 receptors enable the airways of the lung to dilate, allowing for a deeper breath to be taken, which is helpful if you are running from a predator.

Airway dilation is helpful in other situations as well, such as bronchitis and asthma. Beta2 agonists are drugs that can stimulate beta2 receptors alone or without significant stimulation of the other receptors.

Beta1 receptors are located in the heart muscle, and when those receptors are stimulated, the heart rate increases. Terbutaline sulfate can be used at higher doses to stimulate the beta1 receptors as well as the beta2 receptors.

How This Medication Is Used

Beta2 agonists have another effect that might be useful: they delay labor during pregnancy. This is not a common use in veterinary medicine, but this medication could be used to prevent premature labor should a patient be deemed at risk for this situation.

Terbutaline sulfate can be given as a tablet to treat dogs with bronchitis or other lung diseases. It is not helpful for tracheal collapse.

It can be kept on hand as an injectable to use at home for asthmatic cats when they have an after-hours breathing crisis.

Terbutaline sulfate can be used as a metered dose inhaler for dogs or cats who need periodic airway dilation.

Terbutaline sulfate can be used to increase heart rate in patients where the natural heart rate is too slow and causes collapse.

Terbutaline sulfate tablets are typically given 2-3 times daily. If a dose is accidentally skipped, do not double up on the next dose, as an overdose can result. Store terbutaline sulfate at room temperature, protected from light. Partially used injectable bottles should be discarded.

Side Effects

Stimulating the sympathetic nervous system can produce tremors, increased heart rate, dizziness, and excitement. These effects are generally minor. With an overdose, the heart rhythm may be disturbed, blood pressure can become high, and there may be fever, dilated pupils, and vomiting.

Interactions With Other Drugs

Using terbutaline sulfate with any other drug that stimulates the sympathetic nervous system can increase the chance of getting a heart arrhythmia side effect.

Propranolol is a beta-blocker used in the treatment of heart disease. It has some ability to block beta2 receptors, although it is mostly used for its beta1 receptor effects. This means that propranolol can inactivate terbutaline sulfate.

Digitalis, a heart medication, can also increase the chance of heart arrhythmia with terbutaline sulfate.

Tricyclic antidepressants (such as clomipramine) and MAO inhibitors (like amitraz or selegiline) can increase vascular dilation, another beta receptor effect that is generally significant with terbutaline sulfate alone.

Concerns And Cautions

There are plenty of situations where the stimulation of either beta1 or beta2 beta receptors would be a bad idea:

If possible, the use of terbutaline sulfate should be avoided in these situations.

If using this medication to treat a feline asthma crisis at home, expect the injection to take approximately 15 minutes to show an effect.

It is our policy not to give dosing information over the Internet. 

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