unique Japanese indication, because we can use tolvaptan not
only in hyponatremic patients but also in normonatremic ones.
However, the occurrence of hypernatremia in this study was
relatively frequent compared with the QUEST study. Hypernatremia
sometimes results in central nervous system disturbance,
and therefore careful observation of serum sodium levels is
essential. We observed that hypernatremia emerged within 3
days in most cases, and frequent measurement of electrolytes
is recommended, especially during the initial phase of tolvaptan
treatment.