Cardiac Glycosides

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Action/Kinetics: Cardiac glyco-sides increase the force and velocity of myocardial contraction (positive inotropic effect) by increasing the refractory period of the AV node and decreasing total peripheral resistance. This effect is due to inhibition of sodium/potassium—ATPase which results in an increase of calcium influx and an increased release of free calcium ions within the myocardial cells. Clinical effects are not seen until steady-state plasma levels are reached. The initial dose of digitalis glycosides is larger (loading dose) and is traditionally referred to as the digitalizing dose; subsequent doses are referred to as maintenance doses. Uses: All types of CHF, including that due to venous congestion, edema, dyspnea, orthopnea, and cardiac arrhythmia. Control of rapid ventricular contraction rate in clients with atrial fibrillation or flutter. Slow HR in sinus tachycardia due to CHF. Supraventricular tachycardia. Prophylaxis and treatment of recurrent paroxysmal atrial tachycardia with paroxysmal AV junctional rhythm. Cardiogenic shock (value not established).

Contraindications: Ventricular fibrillation or tachycardia (unless congestive failure supervenes after protracted episode not due to digitalis), in presence of digitalis toxicity, hyper-sensitivity to cardiac glycosides, beriberi heart disease, certain cases of hypersensitive carotid sinus syndrome, 2nd or 3rd degree heart block. Special Concerns: Use with caution in clients with ischemic heart disease, acute myocarditis, hyper-trophic subaortic stenosis, hypoxic or myxedemic states, Adams-Stokes or carotid sinus syndromes, cardiac amyloidosis, or cyanotic heart and lung disease, including emphysema and partial heart block. Those with carditis associated with rheumatic fever or viral myocarditis are especially sensitive to digoxin-induced disturbances in rhythm. Electric pacemakers may sensitize the myocardium to cardiac glycosides. Also use with caution and at reduced dosage in elderly, debilitated clients, pregnant women and nursing mothers, and newborn, term, or premature infants who have immature renal and hepatic function and in reduced renal and/or hepatic function. Side Effects: Cardiac glycosides are extremely toxic and have caused death even in clients who have received the drugs for long periods of time. There is a narrow margin of safety between an effective therapeutic dose and a toxic dose. Over-dosage caused by the cumulative effects of the drug is a constant danger in therapy with cardiac glycosides. Digitalis toxicity is characterized by a wide variety of symptoms, which are hard to differentiate from those of the cardiac disease itself.

CV: Changes in the rate, rhythm, and irritability of the heart and the mechanism of the heartbeat. Extrasystoles, bigeminal pulse, coupled rhythm, ectopic beat, and other forms of arrhythmias have been noted. Death most often results from ventricular fibrillation. Cardiac glyco-sides should be discontinued in adults when pulse rate falls below 60 beats/min. All cardiac changes are best detected by the ECG, which is also most useful in clients suffering from intoxication. Acute hemorrhage. Oral: Excessive salivation, sensitive gag reflex. GI: Anorexia, N&V, epigastric distress, abdominal pain, diarrhea, bowel necrosis. Clients on digitalis therapy may experience two vomiting stages. The first is an early sign of toxicity and is a direct effect of digitalis on the GI tract. Late vomiting indicates stimulation of the vomiting center of the brain, which occurs after the heart muscle has been saturated with digitalis. CNS: Headaches, fatigue, lassitude, irritability, malaise, muscle weakness, insomnia, stupor. Psychotomimetic ef fects (especially in elderly or arterio-sclerotic clients or neonates) including disorientation, confusion, depression, aphasia, delirium, hallucinations, and, rarely, convulsions. Neuromuscular: Neurologic pain involving the lower third of the face and lumbar areas, paresthesia. Visual disturbances: Blurred vision, flickering dots, white halos, borders around dark objects, diplopia, am-blyopia, color perception changes. Hypersensitivity (5- 7 days after starting therapy): Skin reactions (urticaria, fever, pruritus, facial and an-gioneurotic edema). Other: Chest pain, coldness of extremities. Drug Interactions Aminosalicylic acid / l Effect of digitalis glycosides due to l absorption from GI tract Antacids / l Effect of digitalis glycosides due to l absorption from GI tract

Corticosteroids / Can cause hypoka-lemia.

Epinephrine / T Chance of cardiac arrhythmias

Erythromycin / T Digoxin blood levels.

Muscle relaxants, nondepolarizing / T Risk of cardiac arrhythmias Sympathomimetics / T Chance of cardiac arrhythmias Succinylcholine / T Chance of cardiac arrhythmias

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