Decreased potassium levels are most concerning when a patient is taking which heart medication?

• A. Amiodarone
• B. Warfarin
• C. Digoxin
• D. Lisinopril

Answer: (C)

Low potassium makes digoxin toxicity more likely. Digoxin works by inhibiting the Na+/K+ ATPase pump. When potassium is low, there’s less competition for that binding site, so more digoxin binds the pump, causing stronger inhibition, higher intracellular calcium, and a risk of dangerous arrhythmias. Among the listed medications, this electrolyte abnormality most directly worsens the effects of digoxin. The other drugs don’t have their safety tied to low potassium in the same immediate way—one tends to raise potassium (hyperkalemia risk) rather than worsen digoxin’s effects, and others aren’t primarily affected by potassium levels.