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Heiman.pharm.CHF.1
Cardiac Glycosides
| Question | Answer |
|---|---|
| Mechanism | Inhibition of the Na-K ATPase pump Causes increased intracellular Na Causes increased Na/Ca exchange leading to increased Ca in sarcoplasmic reticulum |
| Mechanism cont'd | Leads to activation of cardiac contractile proteins, actin and myosin Causes increased force of contraction of cardiac muscle |
| Effects | Increased force of myocardial contraction Depression of the SA node by stimulating vagal activity Prolongation of the AV node conduction via vagal stimulation Increased refractory period of AV node Increased peripheral resistance |
| Kinetics | 60-80% oral absorption Very little metabolism Renal excretion Up to 75% unchanged Half-life of 36 hours Not removed by dialysis |
| Cautions | Use cautiously in renal insufficiency Different brands are not bioequivalent Dosage adjustments needed for patients with thyroid disease |
| Cautions | Electrolyte imbalances Hypokalemia makes myocardium more sensitive to digoxin, may decrease inotropic effect Hypercalcemia predisposes to digoxin toxicity, hypocalcemia may make digoxin ineffective Hypomagnesiemia predisposes to digoxin toxicity |
| Contraindications | Contraindicated in: Ventricular fibrillation Ventricular tachycardia |
| Monitoring | Digoxin levels Therapeutic level 1 – 2 ng/ml Electrolyte levels Heart rate |
| Adverse Effects | Anorexia Nausea / vomiting Abdominal discomfort Headache Weakness Visual disturbances Blurred vision, halo effect |
| Adverse Effects, Arrhythmias | Ventricular tachycardia Multifocal PVCs Atrioventricular block Bradycardia Nodal rhythms Atrial fibrillation Ventricular fibrillation |
| Signs of Cardiac Glycoside Toxicity | Fatigue Anorexia Weakness Nausea Arrhythmias Diarrhea Visual disturbances |
| Cardiac Glycosides – Drug Interacations | Those that decrease digoxin levels Antacids Antineoplastics Activated charcoal Cholestyramine (Questran) Colestipol (Colestid) Kaolin/pectin Metoclopramide (Reglan) |
| Drugs That Increase Digoxin Levels | Amiodorone Bepridil Cylosporine Indomethacin Itraconazole Macrolids Propafenone Quinidine Spironolactone Verapamil Tetracycline |
| Names | Digoxin (Lanoxin, Digitek, Lanoxicaps) PO, IV |
Created by:
DianaB
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