Vasopressor Pharmacology

Vasopressors are vasoactive medications that increase systemic vascular resistance (SVR) and mean arterial pressure (MAP) through stimulation of adrenergic receptors (alpha-1, beta-1) or non-adrenergic receptors (V1 vasopressin receptors). They are classified into catecholamines (norepinephrine, epinephrine, dopamine, phenylephrine) and non-catecholamines (vasopressin, angiotensin II). Alpha-1 receptor stimulation on vascular smooth muscle activates the Gq-phospholipase C-IP3 pathway, increasing intracellular calcium and producing arterial and venous vasoconstriction, thereby raising SVR and MAP. Beta-1 receptor stimulation in the myocardium activates the Gs-adenylyl cyclase-cAMP pathway, increasing heart rate (chronotropy), contractility (inotropy), and conduction velocity (dromotropy), thereby increasing cardiac output. V1 (vasopressin-1a) receptors on vascular smooth muscle couple to Gq proteins and produce vasoconstriction independent of catecholamine pathways, which is particularly valuable in vasodilatory shock where catecholamine receptor downregulation occurs. Dopaminergic (D1) receptors in renal and mesenteric vasculature produce vasodilation at low dopamine doses. The clinician selects vasopressors based on the underlying shock physiology: norepinephrine (first-line for septic shock per Surviving Sepsis Campaign) provides potent alpha-1 with moderate beta-1 stimulation; vasopressin (0.03-0.04 units/min) is added as a catecholamine-sparing adjunct; epinephrine provides combined alpha-1 and beta-1 effects for...