Sun14November1246PM 31

Are the following true of digoxin?

True / False

Increases intracellular potassium Correct

Promotes acetylcholine release at cardiac muscarinic receptors Correct

ST segment depression on ECG is a sign of toxicity Correct

Decreases the refractory period of the bundle of His Correct

Has on oral bioavailability of 70% Incorrect answer selected

Explanation

Digoxin is cardiac glycoside that can be used in the treatment of atrial fibrillation and atrial flutter. It has direct and indirect mechanisms of action.

In the direct mechanism digoxin Inhibits cardiac Na/K-ATPase, increasing intracellular sodium. This increases exchange for calcium via the Na+/Ca2+ pump, thus increasing intracellular calcium which will act as an inotrope. The resultant decrease in intracellular sodium decreases conductivity and increases the refractory time of the bundle of His.

In the indirect mechanism digoxin also causes the release of acetylcholine at the cardiac muscarinic receptors resulting in prolongation of the refractory period at the AV node and bundle of His.

Prolonged PR interval, ST segment depression, T wave flattening and shortened QT are therapeutic, not toxic ECG signs.

Digoxin has an oral bioavailability of 70% with a volume of distribution of 5-10 L/Kg.

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Times answered: 250