Formulary Monographs [CARDIAC DRUGS, 2404]
CARDIAC DRUGS
2404
CARDIAC DRUGS
Cardaic Glycosides

These have a positive inotropic effect and reduce the size of a failing dilated heart leading to increased cardiac output and increased efficiency. They increase myocardial excitability and automaticity, depress conducting tissue and increase vagal activity. Digoxin’s half-life is more than 24 hours. The therapeutic blood level is 0.8 to 2.0mg/ml.

General Indications(Digoxin)
Cardiac failure, atrial fibrillation, atrial flutter, paroxysmalatrial tachcardia.

Cautions/Side effects
These usually occur at toxic serum levels above 2.0 mg/ml, but may do so in the therapeutic range especially in the elderly. Fatigue,anorexia, nausea, visual disturbances, muscle weakness, psychic symptoms, abdominal pain, dizziness, vomiting, cardiacdisturbance - heart block,cardiac arrhythmias. Toxicity most likely with hypokalemia. Treat digoxin - induced heart block with atropine; PVC’s and ventricular tachycardia with i.v. phenytoin. These drugs must be used with caution:
(1) following acute myocardial infarction;
(2) within 14 days of previous treatment with cardiac glycosides;
(3) in the presence of Quinidine treatment;
(4) in the presence of severe potassium imbalance;
(5) in renal insufficiency and in the elderly (most of whom have some renal impairment).

DoseRange( Digoxin)
Loading dose 0.75 - 1.5mg in first day (e.g. 0.5mg initially and 0.25mg every 6 - 8 hours until desirable effect is reached or toxicity occurs). Maintenance dose 0.125-0.25mg.
Children - oral: 25 - 35 mcg/kg every 6 hours until digitalization, then 25 - 35% of loading dose for maintenance.

Anti-Arrhythmics
The physiology of arrhythmias is complex and the action of drugs used in their treatment equally so.
CLASS I - Membrane stabilizers
CLASS II - Drugs which reduce sym- pathetic activity
CLASS III - Drugs which prolong the effective refractory period and
duration of the action potential
CLASS IV - Drugs which interfere with calcium transfer into the cell