Cardiac glycosides Flashcards
Digoxin inhibits which mechanism of transport in the cell membrane?
Na+/K+/adenosine triphosphatase
Why is external calcium referred to as trigger calcium in the cardiac myocyte?
Because it is the trigger for release of intracellular calcium stores from the sarcoplasmic reticulum
Digoxin is removed from the body by _____ excretion
Urinary; as a result, renal failure can cause digoxin toxicity
What is the mechanism of action of digoxin?
By inhibiting the cardiac myocyte sodium/potassium pump, digoxin also prevents sodium/calcium exchange, increasing intracellular calcium concentration
What is the effect of increased intracellular calcium on cardiac function?
Positive inotropy
By what mechanism is digoxin beneficial in atrial fibrillation?
Digoxin decreases conduction at the atrioventricular node and causes depression of the sinoatrial node
What are three common gastrointestinal complaints that occur with digoxin use?
Nausea, vomiting, and diarrhea
What vision complaint can occur with digoxin use?
Blurry yellow vision
What potential heart problem can arise with the use of digoxin?
Arrhythmia
What factors increase the likelihood of digoxin toxicity?
- Kidney failure (because of decreased excretion)
- Hypokalemia
- Quinidine, verapamil, amiodarone (due to displacement of tissue-binding sites)
What is the approach to treatment of digoxin toxicity?
- Slow normalization of potassium levels
- Lidocaine, a cardiac pacer
- Anti-digoxin antibodies
- Magnesium
How does hypokalemia increase the toxicities of digoxin?
Potassium competes with digoxin at the same binding site in sodium/potassium adenosine triphosphatase, so hypokalemia allows for increased digoxin binding, and thus increased digoxin toxicities
What is the ultimate mechanism of action of cardiac glycosides?
To increase intracellular calcium (thereby acting as a positive inotrope), and to stimulate the vagus nerve
