Which of the following is not an inotrope?

Adenosine is not classified as an inotrope. Inotropes are agents that alter the force or energy of contraction of the heart muscle, increasing the contractility to improve cardiac output in conditions such as heart failure or low cardiac output states.

Dobutamine, dopamine, and digoxin all affect cardiac contractility. Dobutamine primarily enhances cardiac output by stimulating beta-adrenergic receptors, leading to increased heart contractility. Dopamine can exert positive inotropic effects at certain dosages by stimulating beta-adrenergic receptors, while at other dosages, it primarily acts on dopamine receptors to improve renal perfusion. Digoxin increases the force of contraction by inhibiting the Na+/K+ ATPase pump, leading to increased intracellular calcium levels in cardiac myocytes, enhancing myocardial contractility.

In contrast, adenosine does not have significant effects on cardiac contractility. Instead, it primarily functions as a vasodilator and has a role in the modulation of heart rate, particularly through its action on the atrioventricular node to slow conduction. This makes it useful for certain types of supraventricular tachycardias but not as an inotropic agent. Thus, adenosine's pharmacological effects differ fundamentally