Chapter 19: Adrenergic Drugs – The Sympathetic Response

Adrenergic Drugs – The Sympathetic Response drugs act upon adrenergic receptor sites—alpha-adrenergic (alpha-1 and alpha-2), beta-adrenergic (beta-1 and beta-2), and dopaminergic receptors—that normally respond to endogenous catecholamines like epinephrine, norepinephrine, and dopamine. The physiological effects depend entirely on the receptor subtype stimulated: alpha-1 stimulation predominantly results in vasoconstriction and mydriasis, while beta-1 stimulation causes increased heart contractility, rate, and electrical conduction (positive inotropic, chronotropic, and dromotropic effects). Beta-2 receptor activation is crucial for therapeutic bronchodilation and relaxation of uterine and GI smooth muscle. Adrenergics can be classified by their mechanism of action (direct, indirect, or mixed-acting) and their selectivity, which can often be dose-dependent, as seen with dopamine and epinephrine. Clinically, these medications treat conditions such as asthma (using beta-2 agonists like salbutamol), nasal congestion, glaucoma, and critically, cardiovascular failure or shock using vasoactive sympathomimetics (pressors) like dobutamine, norepinephrine, and phenylephrine. Due to the potent cardiovascular and CNS-stimulating effects, nurses must focus assessments on vital signs, cardiac rhythms, and respiratory status, noting that adverse effects include hypertension, tachycardia, tremors, and insomnia. Nursing implementation is critical for high-alert injectable vasoactive drugs, which require administration via a central line with continuous monitoring, and must be treated promptly with phentolamine if extravasation occurs.