An adult female client with chronic kidney disease (CKD) asks the nurse if she can continue taking her over-the-counter medications. Which medication provides the greatest threat to this client?

A. Cough syrup containing codeine should be used with caution but does not pose the same immediate risk to kidney function as magnesium-containing medications. B. Birth control pills may have cardiovascular risks in certain populations but are not directly nephrotoxic. C. Cold medications containing alcohol can cause drowsiness or interact with other medications but are not the most dangerous for CKD. D. Magnesium hydroxide is the greatest threat because magnesium is excreted by the kidneys. In CKD, impaired excretion can lead to hypermagnesemia, causing serious complications such as respiratory depression, cardiac arrhythmias, and cardiac arrest.