A 74-year-old patient has been taking lansoprazole 30 mg daily for 20 years. Following blood tests, an electrolyte change is noted. Which disturbance is most likely?

• A. Hypermagnesemia
• B. Hypomagnesemia
• C. Hyponatremia
• D. Hyperkalemia

Answer: (B)

Long-term proton pump inhibitor use, like lansoprazole, is associated with hypomagnesemia due to reduced intestinal magnesium absorption. This risk increases with duration of therapy and age, so an elderly patient who has been on the drug for many years is the classic scenario for a low magnesium level. Magnesium is crucial for neuromuscular function and helps regulate calcium via PTH; when Mg is low, you can see symptoms like muscle cramps or even more serious issues such as seizures or arrhythmias, and there can be secondary hypocalcemia. The other electrolyte disturbances listed are not typically linked to PPI therapy. Hypermagnesemia would suggest excessive magnesium intake or kidney failure; hyponatremia and hyperkalemia have different common causes and are not characteristic of PPI effects. Therefore, the disturbance most likely is hypomagnesemia.