Heart Failure Flashcards
What is the mechanism of action for the positive Inotropic effects of digoxin?
- Inhibits Na+/K+ pumps of cardiac cell membranes. Increases intracellular Na+ levels, which facilitates Ca++ influx into cells.
- Increased Ca++ equals stronger muscle contractions
What is the mechanism of action for the beneficial neurohormonal effects of digoxin?
- Reduces sympathetic nervous system activation and increases parasympathetic activity leading to a decrease in HR, this enhancing diastolic filling.
- Vagal effects slow SA node conduction
What are the drugs found within the cardiac glycoside class?
digoxin
What are the therapeutic uses for digoxin?
- Treat systolic heart failure: improves symptoms, quality of life, LVEF, and exercise tolerance but does not improve M/M
- Treats supraventricular tachyarrhythmias
What is the half-life of digoxin?
1.5 - 2 days; although much longer if renally impaired
Does digoxin have cytochrome p450 interactions?
Yes, it is a substrate of CYP3A4
What is a therapeutic dose that is acceptable for the treatment of heart failure?
- Generally 0.5 - 1.0 ng/ml
Does digoxin have a small or wide volume of distribution?
large Vd
Why is a digitalizing dose (loading dose) necessary to achieve adequate serum levels in digoxin?
- Used for tachyarrhythmias
- Needed to overcome large Vd
When would a loading dose of digoxin be appropriate and how are they administered?
- When a quick onset of action is needed
- Usually done in hospital
- Loading dose increases risk of toxicity
For what reasons should serum digoxin levels be obtained?
- dosage change
- interacting meds
- questionable compliance
- Change in renal or liver function suspected
- Abnormal ECG
- Suspected loss of efficacy
- Suspected toxicity
Who is at an increased risk for digoxin toxicity?
- Pts. with decreased renal function
- increased myocardial sensitivity
- frequent use of diuretics, laxatives, and other interacting meds
What are some common drug interactions associated with digoxin administration?
- AV heart block when used with Beta-blockers, diltiazem, verapamil
- CYP3A4 inhibitors will increase digoxin levels: quinidine, amiodarone, diltiazem, itraconazole, erythromycin, & clarithromycin
- Hypokalemia, hypercalcemia, and hypomagnesemia will predispose pts to digoxin toxicity
- Antacids may reduce bioavailability
- Antibiotics (alter GI flora)
What are the adverse effects that digoxin may have when administered in patients that may indicate toxicity? KNOW THESE
Van Gough
- N/V, loss of appetite
- Fatigue, weakness, dizziness, HA, neuralgia, confusion, delerium, psychosis
- Vision: blurred, haloes, photophobia, red-green or yellow-green tinted vision
- Almost any kind of cardiac dysrrhythmia
- Sinus bradycardi with pulse < 60
What is the appropriate treatment for digoxin toxicity?
- K+ supplements
- Treat dysrrhythmia with appropriate agent (lidocaine, phenytoin)
- Digoxin Immune Fab (digibind): binds digoxin molecules in blood, inactivating it. Molecules then excreted renally over time
