The oral drug is tolvaptan. It's designed to allow for the removal of plain water through the urine.
If the sodium level in the blood is low, people get a condition known as hyponatremia. Low blood sodium has been linked to increased complications and death in people with heart failure, liver cirrhosis, and other conditions.
Sodium is an essential chemical element that affects the function of cells all over the body.
University of Colorado researcher Robert W. Schrier, MD, and colleagues conducted two clinical trials of tolvaptan in people with low blood sodium due to heart failure, cirrhosis, and other conditions. All of the patients were treated outside the hospital.
In the studies, tolvaptan's positive effects became apparent after four days of treatment. After 30 days of treatment, more than half of the patients getting tolvaptan had normal blood sodium levels. Only a fourth of patients who got inactive placebo pills had normal blood sodium levels after 30 days.
After 30 days, 7% of tolvaptan patients in one study and 15% of tolvaptan patients in the other study had seriously low blood sodium levels. Seriously low blood sodium levels occurred in 35% and 32% of placebo-treated patients.
Side effects of tolvaptan included thirst, dry mouth, and increased urination. More serious side effects -- seen in patients receiving tolvaptan as well as in those receiving the placebo -- included low blood pressure, dizziness, and fainting.
The number of deaths was similar in the tolvaptan and placebo groups.
Schrier and colleagues report the findings in the Nov. 16 issue of The New England Journal of Medicine. In an editorial accompanying the report, Richard M. Hays, MD, of New York's Albert Einstein College of Medicine, warns that patients taking tolvaptan must be watched closely.
"It is clear that careful oversight of the use of this agent is required, not only by means of frequent clinic visits and measurement of [blood sodium levels], but also through daily measurement of body weight by patients," Hays suggests.