Tolvaptan was also in fast-track clinical trials for polycystic kidney disease. In a 2004 trial, tolvaptan, when administered with traditional diuretics, was noted to increase excretion of excess fluids and improve blood sodium levels in patients with heart failure without producing side effects such as hypotension (low blood pressure) or hypokalemia (decreased blood levels of potassium) and without having an adverse effect on kidney function. In a recently published trial (TEMPO 3:4 ClinicalTrials.gov number, NCT00428948) the study met its primary and secondary end points. Tolvaptan, when given at an average dose of 95 mg per day over a 3-year period, slowed the usual increase in kidney volume by 50% compared to placebo (2.80% per year versus 5.51% per year, respectively, p<0.001) and reduced the decline in kidney function when compared with that of placebo-treated patients by approximately 30% (reciprocal serum creatinine, -2.61 versus -3.81 (mg/mL)-1 per year, p <0.001)
FDA has determined that the drug Samsca (tolvaptan) should not be used for longer than 30 days and should not be used in patients with underlying liver disease because it can cause liver injury, potentially leading to liver failure
^Shoaf S, Elizari M, Wang Z, et al. (2005). "Tolvaptan administration does not affect steady state amiodarone concentrations in patients with cardiac arrhythmias". J Cardiovasc Pharmacol Ther10 (3): 165–71. doi:10.1177/107424840501000304. PMID16211205.
^Gheorghiade M, Gattis W, O'Connor C, et al. (2004). "Effects of tolvaptan, a vasopressin antagonist, in patients hospitalized with worsening heart failure: a randomized controlled trial". JAMA291 (16): 1963–71. doi:10.1001/jama.291.16.1963. PMID15113814.
Gheorghiade M, Niazi I, Ouyang J et al. (2003). "Vasopressin V2-receptor blockade with tolvaptan in patients with chronic heart failure: results from a double-blind, randomized trial". Circulation107 (21): 2690–6. doi:10.1161/01.CIR.0000070422.41439.04. PMID12742979.