USE OF LAXATIVES BY CKD STAGE AND SERUM MAGNESIUM MEASUREMENT STATUS DURING USE OF MAGNESIUM-CONTAINING LAXATIVES

Constipation is an important symptom that frequently occurs in patients with chronic kidney disease (CKD), and effective treatment of constipation is necessary to maintain quality of life. Magnesium (Mg)-containing laxatives are generally the most frequently used, but concerns have been raised about the accumulation of serum magnesium associated with deteriorating kidney function. To avoid abnormal serum Mg accumulation, serum Mg levels must be monitored and the dose adjusted as necessary. However, it is unclear which laxatives are prescribed for patients at each stage of CKD and how many patients prescribed Mg-containing laxatives have their serum Mg levels measured at least once a year in clinical practice. The aim of this study is to investigate the usage patterns of laxatives according to CKD stage and the actual clinical practice of measuring serum Mg levels in patients with CKD prescribed Mg-containing laxatives.

Patients who visited our outpatient clinic at the Japanese Red Cross Wakayama Medical Center between January 2022 and December 2022 were screened. Of these, 1,891 were prescribed any laxatives at least once a year, and 1,842 could be categorized by CKD stage. Laxatives were classified into six types: Mg-containing laxatives, stimulant laxatives, epithelial function modifiers, polymeric compounds, bile acid transporter inhibitors, and sugar laxatives. For patients prescribed Mg-containing laxatives, this study investigated whether serum Mg levels had been measured at least once during the study period. For patients with multiple visits during the study period, the most recent data was used.

The average age of the 1,842 patients was 70.1 years old, with 51.7% being male. Of these, 198 were in CKD stage 1, 774 in stage 2, 449 in stage 3a, 233 in stage 3b, 135 in stage 4, and 53 in stage 5. 1,654 patients (89.8%) were prescribed one laxative agent, 174 patients (9.4%) were prescribed two agents, and 14 patients (0.8%) were prescribed three agents. No patients were prescribed four or more agents. The proportion of patients using only one agent remained consistently above 80% across all CKD stages. The number of patients prescribed Mg-containing laxatives according to the number of agents was as follows: 983/1,654 (59.4%) for one agent, 151/174 (86.8%) for two agents, and 14/14 (100%) for three agents. Overall, 62.3% of patients were prescribed Mg-containing laxatives. Of the 1,148 patients prescribed Mg-containing laxatives, serum magnesium concentrations were measured in 283 patients (24.7%). The proportion of serum Mg measurements according to CKD stage was as follows: 22% for CKD stage 1, 17% for stage 2, 21% for stage 3a, 43% for stage 3b, 50% for stage 4; and 84% for stage 5. No patient with CKD stages 1 or 2 exceeded the upper limit of the reference range (above 2.6 mg/dL) for serum Mg concentration, whereas 1.6%, 3.2%, 21.7% and 6.3% of those with CKD stages 3a, 3b, 4 and 5 did so, respectively.

This study showed that Mg-containing laxatives were commonly prescribed across all stages of CKD. In addition, it revealed that serum Mg concentrations in patients prescribed Mg-containing laxatives annually measured only 50% of patients with CKD stage 4 and 84% of those with stage 5. It is necessary to promote regular serum magnesium assessments for the safe use of Mg-containing laxatives.