A client who has been receiving diuretic therapy is admitted to the emergency department with a serum potassium level of 3.0 mEq/L. The nurse should alert the health care provider immediately that the client is on which medication?

A. Metoprolol (Lopressor) 12.5 mg orally daily: Metoprolol is a beta-1 selective blocker used to manage hypertension and cardiac conditions. While it can affect heart rate and conduction, it does not have a direct interaction with potassium levels that significantly increases acute risk in hypokalemia. Monitoring is important, but it is not the most urgent concern. B. Ibuprofen (Motrin) 400 mg every 6 hours: Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that can affect renal perfusion and, in some cases, lead to hyperkalemia rather than hypokalemia. It does not significantly increase the risk of toxicity in the setting of low potassium levels, so it is not the priority medication of concern. C. Oral digoxin (Lanoxin) 0.25 mg daily: Hypokalemia increases the risk of digoxin toxicity because potassium and digoxin compete for the same binding sites on the Na⁺/K⁺-ATPase pump. Low potassium enhances digoxin binding, leading to increased intracellular calcium and a higher risk of life-threatening dysrhythmias such as ventricular arrhythmias and heart block. D. Lantus insulin 24 U subcutaneously every evening: Insulin promotes the intracellular shift of potassium, which can lower serum potassium levels. While this may contribute to hypokalemia, it does not directly increase the risk of acute toxicity in the same way as digoxin. The primary concern is the potentiation of digoxin toxicity rather than insulin use.