Inotropic Agents: Digitalis

Main Uses: Congestive Heart Failure Aim: Alleviate present and future symptoms   Main Effects: Slows the heart rate, so ventricular filling is improved Augments cardiac contraction Digitalis is unique among other Ionotropic agents in that while improving contractility it does not cause tachycardia but rather bradycardia.

Mechanism of Action Direct Action: Digitalis binds to the sodium pump on the myocardial cell membrane and inhibits its function. This pump when inhibited causes a rise in the amount of sodium inside the heart cell, which then exchanges it for calcium through the cell membrane, as calcium rises inside the heart cell contractile mechanism becomes more optimal and stronger. Indirect Action: Parasympathetic nerve activation results in sinus node slowing and thus bradycardia. It also inhibits the Atrio-Ventricular Node. Pharmacokinetics: Half-life: 1.5 days Excretion: 60% through kidneys, 30% by the Liver Body weight is crucial in determining the loading dose, as in a small child with low skeletal muscle mass; less of the loading dose will bind to skeletal muscles and will rather rise the blood digoxin level and cause toxicity.

O T H E R - I N O T R O P I C - A G E N T S
D R U G	D O S A G E
Dobutamine (I.V.) Dopamine (I.V.) Isoproterenol (I.V.) Epinephrine (I.V.) Amrinone (I.V.)     Milrinone (I.V.)	5-15 µg/kg/min 3-15µg/kg/min 0.05-1.0 µg/kg/min 0.05-1.0 µg/kg/min Loading dose 5-10 µg/kg over 2-3 min Maintenance dose 5-10 µg/kg/min Loading dose 50 µg/kg over 10 min Maintenance dose 0.375-0.75 µg/kg/min