Visual Summary
Digoxin, Inotropes, and Vasopressors
Module 6 — Introduction to Medical Pharmacology
Digoxin
Mechanism
Sodium-Potassium ATPase Inhibition
- Less calcium removed from the cell by the sodium-calcium exchanger
- Increased intracellular calcium, increased contractility
- Reduces hospitalizations, not mortality
Toxicity
Narrow Therapeutic Index
- Hypokalemia is the key risk factor
- Classic finding: yellow-green visual disturbance
- Can cause dangerous arrhythmias
Two Mechanisms of Inotropic Support
Receptor-Dependent
Dobutamine
- Beta-1 receptor agonist
- Less effective with downregulated receptors
Receptor-Independent
Milrinone
- Phosphodiesterase type 3 inhibitor
- Effective despite downregulated receptors
- Also produces vasodilation
Inotrope Versus Vasopressor
Inotrope: increases contractility
Vasopressor: increases vascular tone
Norepinephrine: preferred vasopressor in cardiogenic shock