A 75-year-old woman is using digoxin for atrial fibrillation. Her recent labs show potassium 4.8 mmol/L, calcium 2.4 mmol/L, eGFR 74 mL/min. Which of the patient's current parameters put her at an increased risk of digoxin toxicity?

A 75-year-old woman is using digoxin for atrial fibrillation. Her recent labs show potassium 4.8 mmol/L, calcium 2.4 mmol/L, eGFR 74 mL/min. Which of the patient's current parameters put her at an increased risk of digoxin toxicity?

• A. Potassium levels
• B. Calcium levels
• C. eGFR
• D. Sodium levels

Answer: (A)

Digoxin toxicity risk is driven mainly by how quickly the drug is cleared from the body and by electrolytes that affect its action on the heart. Digoxin is cleared primarily by the kidneys, so any decline in renal function can let the drug accumulate and raise toxicity risk. In this patient, the eGFR of 74 mL/min indicates some reduction in kidney function compared with optimal clearance, which can increase digoxin exposure. Potassium and calcium levels influence how digoxin affects cardiac tissue, but the current values do not place her at higher risk: potassium is within the normal to high end of the range, and calcium is normal. Hypokalemia would raise toxicity risk because it increases digoxin binding to the Na+/K+-ATPase, but that isn’t present here. Therefore, the parameter most contributing to increased risk is the reduced kidney function reflected by the eGFR.

Digoxin toxicity risk is driven mainly by how quickly the drug is cleared from the body and by electrolytes that affect its action on the heart. Digoxin is cleared primarily by the kidneys, so any decline in renal function can let the drug accumulate and raise toxicity risk. In this patient, the eGFR of 74 mL/min indicates some reduction in kidney function compared with optimal clearance, which can increase digoxin exposure.

Potassium and calcium levels influence how digoxin affects cardiac tissue, but the current values do not place her at higher risk: potassium is within the normal to high end of the range, and calcium is normal. Hypokalemia would raise toxicity risk because it increases digoxin binding to the Na+/K+-ATPase, but that isn’t present here. Therefore, the parameter most contributing to increased risk is the reduced kidney function reflected by the eGFR.