What distinguishes milrinone from other inotropic agents?

Milrinone is distinguished from other inotropic agents primarily because it inhibits phosphodiesterase (PDE). Specifically, milrinone is a PDE3 inhibitor, which leads to an increase in intracellular cAMP levels. This increase enhances myocardial contractility, providing inotropic support to the heart, and also has vasodilatory effects, reducing systemic vascular resistance.

This mechanism of action is different from that of traditional inotropic agents, such as dobutamine or dopamine, which primarily work through β-adrenergic stimulation to increase heart rate and contractility. In contrast, milrinone's unique mechanism allows it to increase cardiac output while also promoting vasodilation, making it particularly useful in certain cardiac conditions where both cardiac performance and vascular resistance need to be addressed.

The other choices do not accurately represent the unique properties of milrinone. It is neither a β-adrenergic agonist nor an α-adrenergic agonist, and it does not function solely as a vasoconstrictor; rather, it facilitates vasodilation due to its phosphodiesterase inhibitory activity.