Which drugs contribute to hyperkalemia by inhibiting uptake by the heart via Na+/K+ ATPase?

• A. Digitalis and Propranolol
• B. Furosemide and Spironolactone
• C. Acetazolamide and Mannitol
• D. Calcium gluconate and Sodium bicarbonate

Answer: (A)

Potassium movement into heart cells is driven by Na+/K+-ATPase, which pumps K+ into cells while pumping Na+ out. When this pump is inhibited, less K+ is taken up by cardiac cells, so extracellular (serum) potassium rises.

Digitalis directly inhibits Na+/K+-ATPase in cardiac tissue, so it reduces the heart’s uptake of potassium and can contribute to hyperkalemia. Propranolol, a nonselective beta-blocker, decreases Na+/K+-ATPase activity in the heart and also lowers insulin release (which normally helps drive potassium into cells), both of which lessen cellular potassium uptake and can raise serum potassium.

The other options don’t share this mechanism: diuretics like furosemide increase potassium loss; spironolactone spares potassium but doesn’t inhibit the heart’s Na+/K+-ATPase; acetazolamide and mannitol don’t inhibit the pump in the heart; calcium gluconate and sodium bicarbonate are treatments for hyperkalemia, not contributors via pump inhibition.