Conivaptan HCl for Injection (Vaprisol): A Vasopressin Antagonist for the Management of Euvolemic Hyponatremia

140 P&T® • March 2007 • Vol. 32 No. 3 INTRODUCTION Hyponatremia, a common electrolyte disorder, is defined as a serum sodium level of less than 135 milliequivalents per liter (mEq/L). The estimated prevalence of hyponatremia in the U.S. ranges from 3.2 to 6.1 million persons per year. About 1% of patients have an acute and symptomatic presentation of hyponatremia, and 4% are reported to have an acute presentation but no symptoms. Another 15% to 20% of patients have chronic and symptomatic hyponatremia, and 75% to 80% of patients have chronic hyponatremia but are asymptomatic. Most patients have asymptomatic hyponatremia; however, when symptoms appear, sodium levels usually drop below 120 mEq/L. Usually, symptoms are nonspecific, such as headache, lethargy, and nausea. In severe cases, neurological manifestations, including seizures and coma, may occur. Hyponatremia is common in hospital and ambulatory settings. The prevalence of hyponatremia in nursing-home residents was studied in a retrospective and prospective record review at a Veterans Affairs facility. Of 119 patients studied, 18% of patients were found to be hyponatremic according to random serum sodium levels, and a 12-month screening series revealed that 53% of patients had experienced at least one episode of hyponatremia during the study period. An acute and symptomatic episode of hyponatremia may be associated with morbidity and mortality. Mortality rates as high as 17.9% have been reported in hospitalized patients. Even in patients with mild chronic hyponatremia, who are normally considered asymptomatic, the morbidity rate is high. The incidence of falling was higher in patients with a mean serum sodium level of 126 ± 5 mEq/L (21.3%) than in those without hyponatremia (5.3%). The adjusted odds ratio was 67, with a 95% confidence interval (CI) of 7.5 to 607 (P < 0.001). In addition to the morbidity and mortality associated with hyponatremia, this condition is costly to treat. The direct costs of managing hyponatremia range from $1.6 to $3.6 billion per year in the U.S.