A client with a history of heart failure on digoxin therapy asks why potassium levels matter. Which statement is accurate?

• A. High potassium reduces digoxin effectiveness
• B. Low potassium increases the risk of digoxin toxicity
• C. Potassium levels do not affect digoxin action
• D. Potassium levels only matter if the patient also has diabetes

Answer: (B)

Potassium levels influence how digoxin works because digoxin binds to the Na+/K+ ATPase pump in heart cells, and extracellular potassium competes with digoxin for that binding. When potassium is low, more digoxin can bind to the pump, causing greater inhibition of the pump, higher intracellular calcium, and a stronger, but potentially toxic, cardiac effect. This makes toxicity more likely in hypokalemia, which is why the statement that low potassium increases the risk of digoxin toxicity is accurate. Clinically, this is especially important in heart failure patients on digoxin who may also be taking diuretics that lower potassium; monitoring and maintaining normal potassium helps prevent harmful digoxin effects. Signs of toxicity can include GI symptoms, confusion, visual changes, and dangerous arrhythmias. The other statements don’t capture the key interaction: potassium can alter digoxin’s action, high potassium tends to reduce binding, and diabetes status isn’t a relevant factor here.