Positive Inotropic Drugs: Cardiac Glycosides
Cardiac glycosides increase the force of myocardial contraction and reduce conductivity within the atrio-ventricular (AV) node. These are most useful in the treatment of supraventricular tachycardias.
Indications: treatment of all degrees of congestive heart failure and supraventiricular arrhythmias (particularly atrial fibrillation).
Contraindications: ventricular fibrillations، intermittent complete heart block, second degree AV block, supraventiricular arrhythmias caused by wolf – Parkinson white syndrome، hypertrophic obstructive cardiomyopathy toxic effects present from prior administration of any digitalis preparation, ventricular fibrillation.
Dose and Administration: Orally, rapid digitalization, 1 – 1.5 mg in divided doses over 24 hours; less urgent digitalization, 250 – 500 mcgs daily (higher dose divided). Maintenance، 62.5 – 500 mcgs daily (higher dose divided) according to renal function and, in atrial fibrillation, on heart-rate response; usual range 125 – 250 mcgs daily (elderly125 mcgs). Emergency loading dose by intravenous infusion Adult, 250 – 500 mcgs, over 10 – 20 minutes, followed by further fractions at intervals of 4 – 8 hours (depending on the response), to a total loading dose of 0.5 – 1mg. Note: The above doses may need to be reduced if digoxin (or another cardiac glycoside) has been given in the preceding 2 weeks. For plasma concentration monitoring, blood should ideally be taken at least 6 hours after a dose.