Efficacy and safety of oral tolvaptan therapy in patients with the syndrome of inappropriate antidiuretic hormone secretion

Objective: Tolvaptan, an oral antagonist of the vasopressin V-2 receptor, has been found to improve hyponatremia in patients with mixed etiologies. This study analyzed a subgroup of patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) to evaluate the efficacy and safety of tolvaptan in this group. Design and patients: Hyponatremic patients in the SALT-1 and SALT-2 studies with a diagnosis of SIADH were identified based on clinical diagnosis by individual study investigators. Subjects were randomized to receive oral placebo (n = 52) or tolvaptan 15 mg daily, with further titration to 30 and 60 mg daily, if necessary, based on the response of serum [Na+] (n=58). Results: In patients with SIADH, improvement in serum [Na+] was significantly greater (P<0.0001) with tolvaptan than placebo over the first 4 days of therapy as well as the entire 30-day study, with minimal side effects of increased thirst, dry mouth, and urination. Only 5.9% of tolvaptan-treated patients had overly rapid correction of hyponatremia as defined by current guidelines. After discontinuation of tolvaptan, serum [Na+] declined to values similar to placebo. A significant positive treatment effect favoring tolvaptan on the physical component, and a near-significant trend on the mental component, was found using the SF-12 Health Survey. Tolvaptan was associated with a significantly reduced incidence of fluid restriction. Conclusions: Results for the SIADH subgroup were analogous to those of the combined SALT population regarding efficacy and safety but demonstrated a greater improvement in the physical component of the SF-12 Health Survey than in the full mixed etiology SALT patient group.