Medicine & USMLE

Digoxin (Old)

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Digoxin is a cardiac glycoside that works by increasing the strength of the heart’s contractions and slowing down the heart rate. It is used clinically to treat atrial fibrillation and heart failure. Digoxin has a narrow therapeutic range, and side effects are seen above dose levels of 2 ng/mL. The risk of toxicity is increased with hypokalemia, so patients should have their potassium levels monitored closely. The earliest sign of digoxin toxicity is GI distress, and later signs include bradycardia, vision changes, and arrhythmias. The apical pulse should be monitored for a full minute before administration, and the digoxin dose should not be given if the heart rate is less than 60 minutes beat per minute.

Key Points

  • Mechanism
    • Cardiac glycoside
      • Inhibits sodium-potassium ATPase, promoting increased force of cardiac contraction, cardiac output, and tissue perfusion; decreases ventricular rate
      • Positive inotropic effect - increased contraction
      • Negative chronotropic effect - decreased heart rate
    • Clinical Use
      • Atrial fibrillation
      • Heart failure
        • Second line drug
    • Side Effects and Adverse Reactions
      • Digoxin toxicity
        • Narrow therapeutic range
          • Greater than 2.0 ng/mL is indicative of digitalis
          • Normal is 0.5-2.0 ng/mL
        • Toxicity increased with hypokalemia
          • Carefully monitor potassium levels, especially if taking a loop diuretic or cortisone drug
          • Digoxin doesn’t necessarily cause hypokalemia, so be aware of that difference. Hypokalemia puts the patient at risk for toxicity.
        • The elderly and those with renal injury are at higher risk for toxicity
      • Signs/Symptoms
        • GI Distress
          • earliest signs of toxicity
          • Anorexia, nausea, vomiting, diarrhea
        • Bradycardia
          • Always assess apical pulse for a full 60 seconds before administering. DO NOT GIVE if heart rate is <60.
        • Vision changes
          • blurred vision, diplopia, white/yellow halos around objects
        • Arrhythmias
          • Contraindicated in ventricular fibrillation and second and third degree heart block
        • Fatigue, weakness
        • Headache