Cardiac Glycosides: Digoxin

Use: Increases contractility of cardiac muscle fibers
Indications: heart failure; heart rate control in atrial fibrillation
Desired results: Slows heart rate; decreases rate of cardiac electrical conduction; increases strength of cardiac muscle contraction. Improves heart failure symptoms by improving peripheral circulation, which increases fluid excretion.

Prototype drug: Digoxin (Lanoxin)—long half-life

• Narrow Therapeutic Window: therapeutic range = 0.5 (to treat HF) - 2.0 (best for atrial flutter or fibrillation) ng/ml
• Low serum potassium level (<3.5) can result in drug toxicity
• Bradycardia, N/V, visual “halos”, confusion
• Antidote: Digoxin immune Fab (Digibind)

Maintenance dose: 0.125 - 0.5 mg/dl. For older adults, dose is usually 0.125 mg/dl
Pulse rate should be above 60 beats/min.
Does not convert atrial fibrillation to normal heart rhythm. For mngmt. of atrial fibrillation, a calcium channel blocker, such as Calan may be prescribed. To prevent thromboemboli resulting from atrial fibrillation, Warfarin is prescribed concurrently w/ other drugs.
In clients w/ failing heart, cardiac glycosides increases myocardial contraction, w/c increases cardiac output and improves circulation and tissue perfusion. Because it decrease conduction through the AV node, the heart rate decreases.
Phenytoin and lidocaine are effective in treating digoxin induced ventricular dyshrythmias.
Lasix, HCTZ and systemic cortisone can cause hypokalemia. Patient should consume potassium rich foods or take potassium supplements.
Antacid can reduce Digoxin absorption so avoid taking it on the same time.

PHOSPHODIESTERASE INHIBITORS - Positive inotropic drug used for acute heart failure treatment
Promotes increase in cardiac muscle contraction, vasodilation

• IV drugs: inamrinone (Inocor), milrinone (Primacor) - increase stroke volume and cardiac output and promote vasodilation. Administered for no longer than 48-72 hours.

Used for short-term acute management of heart failure, requires cardiac monitoring during therapy for severe dysrhythmias can occur.

ATRIAL NATIURETIC PEPTIDE HORMONE
Nesiritide (Natrecor)— diuresis for heart failure treatment
Inhibits  ADH by increasing urine sodium loss. Promote vasodilation, diuresis and natriuresis. Useful for treating clients who have acute decompensated HF w/ dyspnea at rest or who have dyspnea w/ little exertion.