Sympathomimetic medications: Nursing Pharmacology

Sympathomimetics are medications that mimic the effect of endogenous catecholamines, like norepinephrine and epinephrine. As a result, these medications activate the sympathetic nervous system, which in turn triggers the fight or flight response, ultimately increasing the heart rate and blood pressure, as well as slowing down digestion. This response maximizes blood flow to the muscles and brain.

Now, sympathomimetic medications include dobutamine, dopamine, norepinephrine, epinephrine, and isoproterenol. All of them are administered intravenously, while isoproterenol can also be given intramuscularly, and epinephrine can also be administered intramuscularly, as well as through endotracheal tube or inhalation.

Once administered, sympathomimetic medications act by stimulating adrenergic receptors. Now, there are two main groups of adrenergic receptors: the alpha receptors, and beta receptors. Alpha adrenergic receptors are mainly located on the walls of blood vessels of the skin, as well as the gastrointestinal and genitourinary systems, and when stimulated, they cause vasoconstriction and decreased blood flow to these tissues.

On the other hand, beta receptors have two main subtypes: beta-1 and beta-2. Beta-1 adrenergic receptors are mainly located in the heart, and when activated, they increase the heart rate and contractility, which helps pump out more blood. On the other hand, beta-2 adrenergic receptors are found on smooth muscle cells in the walls of blood vessels supplying skeletal muscles and the brain, so their activation leads to vasodilation and increased blood flow to these tissues; and in the lungs, they cause bronchodilation.

Each type of adrenergic agonists stimulate these receptors to a different degree, which makes them useful to treat different conditions. But in general, all of them activate beta-1 receptors, so they all increase heart contractility, helping in the treatment of conditions where the cardiac output is decreased.

Now, all of these medications can be used to treat cardiac decompensation and shock. In addition, dopamine can also be used to treat bradycardia and post-cardiac arrest after shock. Norepinephrine is mainly used to treat acute hypotension and shock. Epinephrine is used to treat cardiac arrest, shock, and anaphylactic reactions; and because of its action on beta-2 adrenergic receptors, it’s also useful to treat acute asthmatic attacks and bronchospasm. Finally, isoproterenol is used in the treatment of cardiac arrest, episodes of heart block, congestive heart failure, shock, and bronchospasm that may occur during anesthesia.

Now, most side effects of these medications are the result of their action on adrenergic receptors. Clients on sympathomimetics may also experience gastrointestinal side effects, such as nausea and vomiting. Sympathomimetics can also be associated with cardiovascular side effects, including hypertension, and tachycardia, while more serious side effects of adrenergic agonists include angina and arrhythmias, while excessive hypertension can even result in cerebral hemorrhage.

Dopamine, epinephrine, and norepinephrine have a boxed warning for extravasation, which can lead to tissue necrosis, sloughing, and gangrene. Finally, epinephrine can cause hyperglycemia in clients with diabetes.

As far as contraindications go, all sympathomimetic medications should be used with caution during pregnancy and breastfeeding, as well as in elderly clients and those with hypertension or coronary artery disease. In addition, dobutamine is contraindicated in clients with hypertrophic cardiomyopathy with outflow tract obstruction.

On the other hand, norepinephrine should be used with caution when there’s hypovolemia or mesenteric or peripheral thrombosis, and clients on this medication should have adequate blood volume to avoid reduced blood flow, ischemia, and tissue hypoxia from the vasoconstriction.

Dopamine is also contraindicated in clients with tachyarrhythmias, ventricular fibrillation, pheochromocytoma, and hypovolemia. Next, isoproterenol is contraindicated in clients with tachyarrhythmias or angina pectoris, as well as in those experiencing cardiac glycoside toxicity. Finally, epinephrine shouldn’t be given to clients with closed-angle glaucoma and those having a non-anaphylactic shock.