Review Question - QID 100535

This patient presents with symptoms that are consistent with acute digoxin toxicity as evidenced by his headaches, vomiting, diarrhea and ventricular dysrhythmia. Another frequent complication of a digoxin overdose is distortion in color vision.

Digoxin is a cardiac glycoside that is often used to treat congestive heart failure and atrial fibrillation. It functions by direct inhibition of the Na+/K+ ATPase in the membranes of heart cells which leads to an increased sodium concentration inside the cell. This decreases the extrusion of calcium by the Na+-Ca2+ exchanger. Consequently, more Ca2+ is pumped into the sarcoplasmic reticulum and when subsequent action potentials excite the cell, a greater than normal amount of Ca2+ is released to the myofilaments which enhances the force of contraction. This is called positive inotropy. Digoxin has a notably low toxic-to-therapeutic ratio and side effects include arrhythmias, nausea, vomiting, anorexia, and blurry yellow vision.

According to Lichtstein, the Na+/K+ ATPase is a major pathway for Na+ and K+ transport across the plasma membrane. Digoxin and oubain are two glycosides that inhibit this enzyme activity by binding to a specific receptor on the membrane. Side effects of this include an increase in excitability of particular myocytes and can possibly result in specific arrhythmias.

According to Morris et al. digoxin is a useful drug in the treatment of heart failure despite not having a significant effect on mortality in the long term. Digoxin decreased hospitalizations related to heart failure and improved symptoms in patients treated for heart failure. Treatment is indicated in heart failure patients with enlarged hearts and low ejection fractions.

Incorrect Answers
Answer 1: Angioedema is a side effect seen with the use of ACE inhibitors, another drug used in heart failure. Angioedema is not seen with digoxin.
Answer 2: Bronchoconstriction is a side effect of nonselective beta-blockers. Bronchoconstriction is not seen with digoxin toxicity.
Answer 4: Digitalis enhances vagal tone. As a result, it increases the refractoriness of the AV node and leads to an increased PR interval rather than a decreased one.
Answer 5: Cough is a common side effect of ACE inhibitor use, not digoxin.