Milrinone

Milrinone is a phosphodiesterase 3 (PDE3) inhibitor medication used primarily in the short-term management of acute decompensated heart failure. It functions as a positive inotrope and vasodilator.

Mechanism of Action:

Milrinone inhibits phosphodiesterase 3, an enzyme found in cardiac and vascular smooth muscle cells. Inhibition of PDE3 increases intracellular cyclic adenosine monophosphate (cAMP) levels. Elevated cAMP in cardiac myocytes enhances calcium influx during action potentials, leading to increased myocardial contractility (positive inotropy). In vascular smooth muscle, increased cAMP leads to vasodilation, reducing both preload and afterload.

Indications:

Milrinone is typically indicated for the short-term intravenous treatment of acute decompensated heart failure in patients who have not responded adequately to conventional therapies such as diuretics, digoxin, and ACE inhibitors. It may also be used in the management of pulmonary hypertension.

Contraindications:

Milrinone is contraindicated in patients with severe aortic or pulmonic valvular disease, known hypersensitivity to milrinone or other bispyridine phosphodiesterase inhibitors, and in those with severe hypovolemia.

Adverse Effects:

Common adverse effects of milrinone include ventricular arrhythmias (e.g., ventricular tachycardia), supraventricular arrhythmias, hypotension, thrombocytopenia, and headache. Less common but potentially serious adverse effects include torsades de pointes and other life-threatening arrhythmias.

Administration:

Milrinone is administered intravenously. Dosage is typically weight-based and adjusted according to the patient's hemodynamic response and tolerance. It is crucial to closely monitor patients receiving milrinone for changes in blood pressure, heart rate, and electrocardiogram.

Pharmacokinetics:

Milrinone has a relatively short half-life, typically ranging from 0.5 to 1 hour in patients with normal renal function. The drug is primarily eliminated via renal excretion. Dosage adjustments are necessary in patients with impaired renal function.

Precautions:

Caution is advised when using milrinone in patients with pre-existing arrhythmias, hypokalemia, hypomagnesemia, or renal impairment. It should be used with caution in patients with hypertrophic cardiomyopathy or other forms of left ventricular outflow obstruction. The long-term safety and efficacy of milrinone have not been established.