Terbutaline Sulfate (Brethine)

Date Published: 09/12/2011
Date Reviewed/Revised: 08/23/2018

(For veterinary information only)

WARNING
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.

Brand Name: Brethine

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

Background

Terbutaline is a type of drug called a beta2 agonist. It is important to understand a bit about the autonomic nervous system, which is the 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 systems, 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 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. The beta2 agonists are drugs that are able to 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

Terbutaline sulfate can be given as a tablet in the treatment of dogs with tracheal collapse, bronchitis, or other lung disease.

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 causing collapse.

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 beta2beta 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.

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