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CHAPTER 22

CHAPTER 22. Cardiac Glycosides and the Treatment of Congestive Heart Failure. Congestive Heart Failure (CHF). CHF due to weakening of the contractile function of the heart Blood and fluid accumulate in the heart, lungs, abdomen, and lower extremities

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CHAPTER 22

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  1. CHAPTER 22 Cardiac Glycosides and the Treatment of Congestive Heart Failure

  2. Congestive Heart Failure (CHF) • CHF due to weakening of the contractile function of the heart Blood and fluid accumulate in the heart, lungs, abdomen, and lower extremities • Decreased cardiac output and blood pressure are unable to meet body requirements • Cardiovascular reflexes cause vasoconstriction, tachycardia, and sodium and fluid retention which try to maintain blood pressure, but usually fail

  3. Cardiac Glycosides • Drugs originally obtained from plant source, Digitalis purpurea and Digitalis lanata • Digoxin and digitoxin are the only cardiac glycosides currently available • Main pharmacologic effect of cardiac glycosides is to increase the contractile force of myocardial contraction • Cardiac glycosides also decrease heart rate and atrioventricular conduction

  4. Mechanism of Action • Cardiac glycosides inhibit Na/K adenosine triphosphatase, the “sodium pump” which causes more Na to remain inside myocardial cells • Increased intracellular Na stimulates Na/Ca exchange that brings more Ca inside heart cells to increase the force of contraction • Cardiac glycosides also stimulate the vagus nerve which decreases heart rate

  5. Pharmacokinetics and Dosing • Digoxin is water soluble and eliminated mostly unmetabolized by the urinary tract • Digitoxin is more lipid soluble, requires metabolism, and has a longer half-life • In acute CHF, initial “digitalization” doses are administered to rapidly attain effective therapeutic concentration • Lower daily maintenance doses are then given to maintain desired therapeutic concentrations

  6. Electrolyte and Cardiac Glycoside Interactions • Low serum potassium (K) levels “hypokalemia” increase drug toxicity and can cause cardiac arrhythmias • High serum potassium levels “hyperkalemia” decrease the actions of the cardiac glycosides • Increased serum calcium levels “hypercalcemia” can increase the actions and toxicity of the cardiac glycosides

  7. Adverse Effects • Common complaints include headache, dizziness, nausea, and vomiting • Visual disturbances “halo effect” around lights often signals overdosage • Bradycardia, ectopic beats, and a variety of other cardiac arrhythmias can occur and can be life-threatening

  8. Diuretic Therapy of CHF • Diuretic drugs are used to eliminate excess sodium and fluid retention • Elimination of excess fluid allows the heart to function more efficiently • Diuretics can be administered with cardiac glycosides and other drugs used to treat CHF

  9. Vasodilator Therapy of CHF • Vasodilator drugs relax and dilate blood vessels • Vasodilation decreases peripheral resistance, allows more efficient blood flow, and usually increases cardiac output egg-Nitrates,Beta blockers, Aldosterone in • Angiotensin-converting enzyme inhibitors and angiotensin receptor blocking drugs are particularly useful in CHF – ACE inh, ARBs

  10. Drugs to Know • Inotropic agents • Digitoxin (Purodigin) • Digoxin (Lanoxin) • Diuretics • Hydrochlorothiazide (Hydrodiuril) • Furosamide (Lasix)

  11. Drugs to know • Vasodilators • Ace inhibitors - enalopril (Vasotec) • ARBs - Losartin • Nitrates - nitroglycerine (TNG) • Aldosterone blockers – spironolactone (Aldactone) • Beta blockers – Propranolol (Inderal)

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