Isoproterenol, also called isoproterenol hydrochloride or isuprel, is a medication that is structurally similar to epinephrine. It helps smooth muscles to relax and increases activity in the heart. Opening bronchial pathways that constrict while a patient is under anesthesia is the most common use for this medication. It starts to work quickly and wears of within a few hours.
Patients who experience bronchospasm can be given isoproterenol to make it easier for them to breathe. Bronchospasm can be caused by an allergic reaction, an asthma attack, or as a symptom of a disease. In this condition, small air passageways, called bronchioles, which are normally only about 0.04 inches (1 mm) in diameter, constrict under the pressure of the muscles around them. Patients who are under anesthesia can be at risk for bronchospasm, and isoproterenol may be administered while a patient is unconscious in order to counteract the condition.
The body has its own remedy for this condition, in the form of adrenaline. This hormone helps the airways to dilate, but once the adrenaline is used up, it is possible for the airways to close again. Epinephrine-like drugs, such as isoproterenol, act in a similar fashion to adrenaline, opening up restricted airways and allowing a patient to breathe normally.
Isoproterenol is also occasionally given to patients who have suffered a cardiac arrest, either as a stop gap treatment until defibrillation can be administered or as a treatment if defibrillation is unnecessary. Additionally, this medication may be used as a part of a treatment for patients who are in shock. In some cases, the drug may also be administered as an inhalant to control symptoms in patients who have chronic bronchitis or asthma.
Unlike epinephrine, isoproterenol specifically targets only certain β receptors in the body. It binds to both β1 and β2 receptors, which increase heart rate and relax the smooth muscles around the bronchial passageways respectively. Epinephrine also stimulates these same β receptors, though it targets certain α receptors as well.
Isoproterenol begins working within a few minutes. After it is administered, a patient’s bronchial passageways open, heart rate rises, and the diastolic blood pressure falls which allows blood to flow more easily through the body. Many patients may also experience heart palpitations, increased alertness and nervousness. This is due to the fact that the drug mimics adrenaline, which is responsible for the “fight or flight” response. The effects of isoproterenol wear off within about three hours.