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CHAPTER 22 PowerPoint Presentation

CHAPTER 22

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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)