Magnesium oxide (MgO) is used to treat constipation. The kidneys are the principal organ involved in the regulation of magnesium (Mg). When MgO is administered to patients with impaired renal function, periodic measurements of serum Mg levels are recommended; however, in acute care hospitals, the measurement of serum Mg levels and the usefulness of pharmacist interventions in such cases has not yet been investigated. Therefore, we investigated the number of patients with impaired renal function that were treated with MgO and subjected to serum Mg measurements. We also examined the incidence of hypermagnesemia and the usefulness of pharmacist interventions in such cases.

The laboratory data of patients that had received MgO between April 1st, 2016, and March 31st, 2017, at Tokyo Bay Urayasu Ichikawa Medical Center were extracted. The enrolled patients were divided into three groups based on their estimated glomerular filtration rate (eGFR; mL/min), which were not adjusted for body surface area: Group A: 45≦eGFR<60, Group B: 30≦eGFR<45, Group C: eGFR<30.

Serum Mg levels were measured in 145 out of 283 patients that received MgO (51.2%). Pharmacist interventions were performed in 0, 1, and 6 cases in Groups A, B, and C, respectively. The numbers of patients who had their serum Mg levels measured in each group were as follows: A: 33 (33.4%), B: 53 (51.5%), and C: 59 (70.2%). Among the patients whose serum Mg levels were measured, the incidence of hypermagnesemia in Groups A–C was 27.3%, 37.7%, and 61.0%, respectively. The incidence of hypermagnesemia was significantly higher in the impaired kidney function group (p <0.01).

The percentage of patients that had their serum Mg levels measured and the incidence of hypermagnesemia were higher in the lower kidney function group. In total, only 51.2% of patients had their serum Mg levels measured, suggesting the presence of potentially undetected cases of hypermagnesemia. Therefore, pharmacist interventions appear to contribute to the early detection of hypermagnesemia when MgO is administered to patients with impaired renal function.