Cardiac glycosides:
• originally isolated from the foxglove plant, Digitalis purpurea
• eg digoxin, digitoxin, ouabain
• inhibit the membrane Na+/K+ ATPase pump increased intracellular Na+ intracellular Ca+ increases due to release from sarcoplasmic reticulum increased force of cardiac contraction
• also alter electrical activity within heart
• have low therapeutic index; toxicity arrhythmias (can be life threatening), anorexia, nausea, diahorroea, drowsiness, fatigue, visual problems
• increased cardiac output, heart rate declines, decrased vasconstriction of arterioles and veins, reduced peripheral and pulmonary oedema
• indicated for chronic heart failure; also used as antiarrhythmic drugs
• interactions – antacids, barbiturates, neomycin, rifampin, sulfasalazine (reduce therapeutic affects); quinidine, verapamil, cyclosporine, tetracycline, erythromycin, itraconazole (increased toxicity of digoxin); beta blockers, calcium blockers (arrhythmias)
• digoxin toxicity – nausea, vomiting, abdominal pain, diarrheoa, headache progresses to irritability, depression, insominia, confusion, vision changes progresses to complete heart block.
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