Efficacy of Tolvaptan on ADPKD Patients

Based on the results of a study entitled "The Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO 3:4) 1)," tolvaptan was approved in March 2014 for the treatment of autosomal dominant polycystic Kidney Disease (ADPKD) in Japan, followed by in other regions such as Europe and Canada. In May 2014, Kyorin University Hospital started administration of tolvaptan to patients with ADPKD. In the clinical setting in which the dosing conditions differ from those in the TEMPO study, aspects that were not addressed in the TEMPO study may be investigated. The present study is a longitudinal clinical study to investigate the changes before and after administration of tolvaptan by employing a method different from that used in the TEMPO study in patients in whom the clinical course of the disease has been monitored since prior to the approval of tolvaptan. The observation period (for a maximum duration of 3 years) of the study was originally planned to be completed on March 31, 2018 and the analyses of study results and the preparation of a research paper until September 2019. However, the study will be extended for another 2 years, because the long-term effects of the drug should be further investigated. The indication approved in Japan defines the target population as those with an eGFR ≥15 mL/min/1.73 m2, but not specifies the upper limit of age. Therefore, the present study will permit the assessment of therapeutic effects of the drug in patients who are older or have more severe renal impairment as compared with in those participating in the TEMPO3:4 and 4.4 studies. Since such patients generally have a greater TKV, the study may also provide information to decide whether the efficacy of tolvaptan differs according to TKV. The present study is a single-arm longitudinal study, unlike the preceding studies that were placebo-controlled studies 1,2); therefore, tolvaptan may be evaluated from different perspectives. Rationale of DNA analysis The association between pathogenic genotype and the effects of tolvaptan has been reported, but the impact of mutation site has not been cleared 2). Genetic analysis for polycystic kidney will be included in the study to decide whether the effects of tolvaptan is associated with mutation site as well as pathogenic genotype (PKD1, PKD2). Validation of alpha as a HtTKV slope Assuming that TKV corrected for the height at the age at measurement (t years old), HtTKVt (mL/m), increases at a constant annual rate (α, %/ per year) and the HtTKV0 is 150 mL/m, the following equation will be satisfied: HtTKVt = 150 (1+α)t. The α value calculated from the equation will be used as an indicator for supplementarily assessing the effect of tolvaptan on HtTKV slope 5,6).