A nurse is caring for a client who has a new prescription for spironolactone and reports that they forgot to tell the provider that they take over-the-counter supplements. The nurse should instruct the client to avoid which of the following supplements?

The correct answer is D: Potassium. Spironolactone is a potassium-sparing diuretic, so combining it with potassium supplements can lead to hyperkalemia, a serious condition with symptoms like muscle weakness and irregular heartbeat. Avoiding potassium supplements is crucial to prevent this interaction. Iron (A), magnesium (B), and calcium (C) are not contraindicated with spironolactone. Iron can be taken separately from spironolactone. Magnesium and calcium are not typically affected by spironolactone.