(for veterinary information only)
BRAND NAME: BRETHINE
Terbutaline is a type of drug called a "beta2 agonist." To understand what that means, it is important to understand something about the autonomic nervous system which is the part of the nervous system involved in the body's "automatic" functions (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. Details of the effects of stimulating each type of receptor is more than this article can address; the relevant receptor for this discussion is the beta2 receptor.
When a fight or flight situation occurs, adrenaline (also called "epinephrine") and its associated neurotransmitter "norepineprhine" 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, a helpful situation if one is running from a predator.
Airway dilation is helpful in other situations as well such as bronchitis and asthma. Developing a drug that could stimulate beta2 receptors without stimulating the other receptors of the sympathetic nervous system would be a highly desirable thing. 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 itself and when beta1 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 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 period airway dilation.
Terbutaline sulfate can be used to increase heart rate in patients where the natural heart rate is too slow and causing collapse.
Stimulating the sympathetic nervous system can produce tremors, increased heart rate, dizziness, and excitement. These effects are generally minor. With overdose, heart rhythm may be disturbed, high blood pressure can result as well as 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 (though it is mostly used for its beta1 receptor effects). This means that it 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 beta receptors (either beta1 or beta2) 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.
Page last updated: 5/24/2019