A client with chronic kidney disease (CKD) has been taking aluminum hydroxide gel. On the basis of this information, the nurse determines that the client is most at risk for which problem?

Aluminum hydroxide is used as a phosphate binder in chronic kidney disease to reduce hyperphosphatemia, a common complication of CKD due to impaired renal phosphate excretion. However, a well-known and clinically significant side effect of aluminum-containing antacids is constipation. Aluminum ions decrease intestinal motility and interfere with the normal peristaltic action of the gastrointestinal tract, leading to constipation, which can be severe in some patients. This is why magnesium-containing antacids (which cause diarrhea) are sometimes alternated with aluminum-containing ones, though magnesium-based products are often avoided in CKD due to the risk of hypermagnesemia. Dehydration (option B) is not a direct consequence of aluminum hydroxide use. Inability to tolerate activity (option C) and impaired physical mobility (option D) are not pharmacological effects of this agent. While CKD itself can cause fatigue and weakness, these are not the risks most attributable to aluminum hydroxide specifically. The nurse should monitor bowel patterns and counsel the patient to increase fluid and dietary fiber intake to help manage constipation while on this medication.