The finding comes from a relatively small double-blind placebo-controlled trial. “The correction in the tolvaptan group was evident from the first day of its use; the majority of patients achieved eunatremia by day 7, and nearly all achieved eunatremia by day 14,” the researchers report.
They explain in their paper in Cancer, online November 5, that while the availability of inhibitors of theV2 receptor of arginine vasopressin hormone has greatly aided the management of hyponatremia, the safety and efficacy of this approach has not been tested in patients with cancer.
Dr. Abdulla K. Salahudeen and colleagues at The University of Texas MD Anderson Cancer Center, Houston, therefore randomized 48 cancer patients with serum sodium levels of 125-130 mmol/L to receive tolvaptan or placebo for 14 days. The primary goal was a sodium level of 136-147 mmol/L.
Both groups received standard of care for hyponatremia, except that they were allowed to drink water to relieve thirst. This was partly because the usual practice of fluid restriction is impractical in cancer patients, and partly in order to lessen the possibility of sodium overcorrection.
Thirty patients completed the study. Hyponatremia was corrected in 16 of 17 patients given tolvaptan (94%) compared to 1 of 13 placebo patients (8%), the authors report.
The targeted sodium correction rate of 6-12 mmol/L per day was not exceeded in any of the tolvaptan group. The main adverse effects were dry mouth, polydipsia and polyuria, which led to a 13% withdrawal rate.
Secondary end points of length of stay and change in mental status were not significantly different between the two groups, Dr. Salahudeen and colleagues report.
“Although tolvaptan was effective for correcting hyponatremia in patients with cancer,” they conclude, “studies with a larger sample size will be required to confirm the current findings, including the outcomes of secondary endpoints.”