Cardiac Glycosides

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pilismok
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179390
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Cardiac Glycosides
Updated:
2012-11-02 19:04:59
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Pharmacology Friedman
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  1. Cardiac physiology: electrical conduction
    • –   Sino-atrial node - pacemaker 
    • –   Atrio-ventricular node - regulator
    • –   Bundle of His
    • –   Purkinje 

  2. Contraction Phisilogy
    • - electrical current
    • - Ca released to sarcoplasm
    • - interacts with troponin
    • - actin-myosin coupling
    • - contraction



  3. Action potential


    • PHASE 0 - Fast sodium Channel
    • PHASE1 - Mild repolarization
    • PHASE2 - Slow calcium channel
    • PHASE 3 - Repolarization (potassium exits the cell)
    • PHASE 4 - Resting (sodium/potassium pump)
  4. FRANK-STARLING CURVE
    • FS Law: Cardiac Output increases with pressure up to a point of congestive heart failure.
    • Cardiac output (V pumped by H in 1 min) = Stroke volume (Vblood in one ventricle before systole) * heart rate.
    • Systole=Contraction, Diastole=Resting
    • Patients with CHF have low cardiac output, b/c heart lost its contractility => FS curve shifts down. When this occurs SV ⇓ and ⇑ preload (LEVP). 
    • Symptoms associated w/ CHF:
    • 1. Edema: ♡ can't pump anymore => fluid is building up in lungs and lower extremities. Use Loop Diuretics, b/c too much fluid.
    • 2. Shortness of breath and exercise intolerance.
    • Cardiac glycosides shift the curve of the graph up

  5. Low output failure: treatment
    • Congestive Heart Failure
    • Treatment
    •         Diet - weight loss/
    •                   low sodium/fat
    •         Diuretics: Loop and KSparing
    •         Cardiac Glycosides
    •         ACE inhibitors
  6. CARDIAC GLYCOSIDE PHARMACOLOGY
    • 1. Increase Contractility of ♡ (for longer and stronger contaction) (LOW DOSE)
    • (↑ inotropic effect)
    • Cardiac Glycosides decrease ability of myocardial cells to pump Ca++ out => Ca++ stays longer in the cell => longer and stronger contraction => ↑ CO

    • 2. Decrease AV node conduction (in order to prevent V fib) (HIGH DOSE)
    • –   Decreased chronotropic effect (↓ heart rate)
    • –   Used in atrial fibrillation
    • AV node prevent conduction of AP from atruim. Person can live with A-fib, but V-fib is fatal. In order to prevent V fib we use Glycosides. Glycosides ↓ AV node conduction => amount of electrical activity going to the ventricles is ↓ 

    • Therapeutic index is narrow: ng/dL
    • CHF dose: 1-2 ng/dL
    • Afib: 1.5-2.5 ng/dL
    • Toxic: >3 ng/dL
  7. EKG


    • p - atrial contraction
    • QRS- ventricular contraction
    • T - repolarization (phase 3)
  8. Therapeutic monitoring
    • 1. Apical Pulse
    • Nurse should always measure apical pulse before administering drug. Do not administer drug if apical pulse <60, b/c patient may be toxic.
    • Cardiac glycosides work on AV node, they prevent conduction from atria. Higher dose => longer P-R interval (time btw atrial and ventricular conduction)=> 10 block has less ♡ beats=>WARNING: b/c patients apical pulse is <60 they could be in 1block. If ignore warning => 3block. 
    • In 30 degree block the gate is completely closed, nothing goes through AV node (person is toxic with cardiac glycosides)
    • 2) Serum drug level
    • Cardiac glycosides have a narrow therapeutic index. Easy to get toxic: ng/dL
    • 3) Serum potassium- caution in hypokalemia
    • We need K in phase 3 (repolarization), if person doesn't have enough K, he can't recover from phase 2 => toxic. Diuretics also  ↓ K level
    • 4) Serum Calcium- caution in hypercalcemia
    • Ca found in phase 2(longer and stronger contraction), to much Ca, person can't get to phase 3. 
    • If patient doesn't have toxic blood level of cardiac glycosides, hypokalemia or hypercalcemia can make them TOXIC

     5) EKG
  9. PHARMACOKINETICS
    • •    Five half lives leads to steady state
    • •    Loading Doses required
    • •    Toxicities - reversed by digoxin immune
    • fab (Digibind®)
    • •    HALF LIFE
    • –   DIGOXIN - 24 HOURS
    • –   DIGITOXIN - 5 days
  10. BIOAVAILABILITY
    •    INTRAVENOUS - 100%

    •    INTRAMUSCULAR - 80%

    •    TABLET - 70%
  11. TOXICITIES
    A-V BLOCK

    SINUS BRADYCARDIA

    ARRHYTHMIAS

    YELLOW-GREEN HALO VISION

    CNS: Headache, weakness, anorexia
  12. TOXICITY THERAPY
    Discontinue Cardiac Glycoside

    Digoxin immune fab (Digibind®)

    Correct hypokalemia

    Antiarrhythmic Agents
  13. THERAPEUTIC USES
    CONGESTIVE HEART FAILURE

     ADJUNCT THERAPY FOR ATRIAL FIBRILLATION

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