Relationship between renal function and serum magnesium concentration in elderly outpatients treated with magnesium oxide

Aims We investigated the relationship between renal function and serum magnesium concentration in elderly patients treated with magnesium oxide (MgO) in an outpatient setting of an urban hospital in Japan. Methods In the present study, 44 elderly outpatients (23 patients with constipation treated with daily oral MgO and 21 untreated patients in the control group) who visited Kameyama municipal medical center were enrolled. Variables were age, sex, weight, height, serum magnesium concentration, serum blood urea nitrogen level, serum creatinine level, use of other magnesium-containing supplements and symptoms associated with hypermagnesemia. We calculated the estimated glomerular filtration rate (eGFR) and classified patients based on eGFR category. Results Compared with the control group, the MgO group showed a significantly higher concentration of serum magnesium (median 2.2 mg/dL [interquartile range 2.1–2.3] vs 2.4 mg/dL [2.2–2.6], P 2.6 mg/dL) was noted only in the MgO group. However, symptoms associated with hypermagnesemia occurred in patients from both groups, with no significant difference between groups. In the MgO group, significant difference was seen in the median serum magnesium concentration between eGFR categories (P