Phase III clinical pharmacology study of tolvaptan.

Purpose: This study aimed to investigate the pharmacokinetics, pharmacodynamics, efficacy and safety of tolvaptan, an orally effective vasopressin V2-receptor antagonist.
Methods: This was a multicenter, randomized, double-blind, parallel group study. Tolvaptan was administered at 7.5 or 15 mg, in combination with furosemide, for 7 days in Japanese heart failure (HF) patients with volume overload that had not resolved despite receiving furosemide.
Results: The blood concentration of tolvaptan was maintained at a higher concentration for a longer time in patients who received 15 mg/day when compared with patients who received 7.5 mg/day. Tolvaptan increased urine volume and increased weight loss dose-dependently when used in combination with furosemide. Importantly, tolvaptan enhanced water diuresis without affecting blood electrolyte levels.
Conclusion: Tolvaptan exerts diuretic effects and causes body weight loss at the low dose of 7.5 mg; however, these effects were less than those elicited by 15 mg tolvaptan.