Abstracts

Rationale: Hyponatremia is a frequent adverse event associated with antiepileptic drugs, which is suspected to occur by the syndrome of inappropriate antidiuretic hormone secretion. A decrease in the serum sodium level can lead to fatigue, headache, vomiting, anorexia, and coma. The aim of the present study was to evaluate the risk factors and prevalence of hyponatremia among epilepsy patients in relation to their antiepileptic drugs therapy. Methods: We retrospectively reviewed 14,749 adult patients (6,789 females) with epilepsy aged from 18 to 103 years who underwent measurement of serum sodium level between January 2006 and December 2017. If multiple measurements were performed in a single patient during the study period, the highest sodium level was used. In this study, we defined hyponatremia as a serum sodium level less than 138 mEq/L according to Common Terminology Criteria for Adverse Events (CTCAE). To extract the factors influencing the serum sodium level, stepwise multiple regression analysis was performed. Furthermore, multiple logistic regression analysis was performed to calculate adjusted odds ratios for grade 3 to 4 hyponatremia, which was defined as a maximum sodium level less than 130 mEq/L. The study protocol was approved by the ethics committee of the National Epilepsy Center (Shizuoka, Japan). Results: During the study period, grade 1 hyponatremia occurred in 3,309 patients (22.5%), and grade 3 to 4 hyponatremia in 498 patients (3.4%). Age and female gender had a significant negative correlation with the serum sodium level. In multiple logistic regression analysis, age, gender, and the concomitant use of valproic acid and carbamazepine were found to be significant risk factors for hyponatremia. Conclusions: We identified risk factors for hyponatremia in a large cohort of Japanese patients with epilepsy. A decrease of sodium level can be caused by multiple factors and our findings may help avoid problems of hyponatremia. Although carbamazepine and valproic acid are both first-line antiepileptic drugs for focal and generalized epilepsy, the sodium level should be monitored when elderly patients are using valproic acid or carbamazepine. Funding: This study was partly funded by a grant-in-aid for Scientific Research C from the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT).