Long-term dosage and serum magnesium level of magnesium oxide

Abstract

In Japan, the number of elderly people is increasing every year. Elderly patients suffering from constipation with lower gastrointestinal motility have also increased. Magnesium oxide (MgO) preparations are often administered as a treatment for constipation over a long term. On the package insert of MgO formulations, there is a boxed warning to measure serum magnesium levels in order to avoid hypermagnesemia. In this study, we investigated serum Mg levels during long-term MgO administration.A total of 613 patients who were administered MgO preparations over a one-year period at Nagasaki University Hospital between April 1, 2010 and August 31, 2012 were included in the study. The serum Cr level and estimated glomerular filtration rate (eGFR) were measured in all patients. Serum Mg levels were measured in 214 patients (34.9%), meaning that in 65.1% of the patients, serum Mg levels was not measured during the MgO dosage period. No correlation was observed between the number of serum Mg measurements and eGFR. We classified eGFR levels as follows: eGFR ≧ 60, 60>eGFR ≧ 45, 45>eGFR ≧ 30, and 30>eGFR. The number of abnormally high Mg cases significantly increased as eGFR decreased. As serum Mg levels were not measured with regularity in 65% of the patients administered MgO formulations, pharmacists should be involved in the management of these patients over a long term.