Urine Osmolality Is a Potential Marker of Longer-Term Efficacy of Tolvaptan in Autosomal Dominant Polycystic Kidney Disease: A Post Hoc Analysis.

Abstract

Total kidney volume (TKV) and estimated glomerular filtration rate (eGFR) are measures of progression and treatment response in autosomal dominant polycystic kidney disease (ADPKD), but utility is limited by the long follow-up required for change assessment. In an analysis of data from the 3-year TEMPO 3:4 trial, we evaluated relationships among a short-term indicator of drug activity (change in urine osmolality [Uosm]) and longer-term outcomes to evaluate Uosm as a potential marker of efficacy. Linear regression modeling and single-point analyses assessed relationships among change in Uosm to week 3, change in TKV to month 12, and change in eGFR to month 36 in subjects treated with tolvaptan (n=961) or placebo (n=483). Multivariate models evaluated the proportion of the tolvaptan treatment effect on eGFR attributable to change in Uosm. Change in TKV to month 12 and Uosm to week 3 each correlated with change in eGFR to month 36, regardless of treatment assignment. A greater decrease in Uosm from baseline to week 3 was indicative of a slower decrease in eGFR to month 36 (slope estimate of -0.01, P <0.00001). The effect of tolvaptan on Uosm accounted for 68.8% of the treatment effect on change in eGFR to month 36. Simulations of TEMPO 3:4 under the null hypothesis (i.e., replacement of all values for change in Uosm from baseline to week 3 with values from the placebo arm only) yielded a Type 1 error rate indicating an acceptable risk of falsely concluding treatment efficacy based on change in Uosm as a trial endpoint. Change in Uosm is a potential biomarker for long-term treatment outcome with tolvaptan and might expedite clinical trials and treatment decision-making for drugs with similar mechanisms of action.