Clin Exp Nephrol DOI 10.1007/s10157-015-1134-y
LETTER TO THE EDITOR
The effect of tolvaptan on kidney function in patients with autosomal dominant polycystic kidney disease Tomoyuki Kawada1
Received: 10 May 2015 / Accepted: 3 June 2015 Ó Japanese Society of Nephrology 2015
Keywords Estimated glomerular filtration rate Autosomal dominant polycystic kidney disease Tolvaptan Validity To the Editor, I greatly appreciate a subgroup analysis by Muto et al. [1], to evaluate the safety and efficacy of tolvaptan in Japanese autosomal dominant polycystic kidney disease (ADPKD) patients. According to the original report [2], the authors specified the concordance and discrepancy of the results by main and sub-analysis. I have some queries on their study outcome with special emphasis on kidney function by estimated glomerular filtration rate (eGFR), because I recently discussed a validation on several estimating procedures of GFR for Asian population [3]. Muto et al. mentioned that they quoted a reference of eGFR calculation by modified Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation [4], but this paper does not handle with CKD-EPI. As the original report [2] quoted a validation study on CKD-EPI modification for Japanese [5], there is a possibility that Muto et al. made a technical error of citation. Concerning to the eGFR, Muto et al. discussed about the lower eGFR in Japanese ADPKD patients at baseline,
which was compared to the original report, and speculated the reason on the difference of stature between Japanese and multi-ethnic patients. There is a fact that the CKD-EPI study equation presents a lower prevalence of CKD than the prevalence by using equation of Modification of Diet in Renal Disease study in Japan and United States. Taking together, I recommend Muto et al. verifying the equation of eGFR in their study. Finally, the authors used Cox regression analysis to know the efficacy of tolvaptan on four end points, and worsening of kidney function was significantly reduced by tolvaptan treatment with hazard ratio (95 % confidence interval) of 0.17 (0.06–0.49). I suppose that the sole variable is treated in the model [2], and small number of events can keep a valid estimate. But the authors speculated the reason of discrepancy of statistical significance on ADPKD-related composite events and kidney pain between main and sub-analysis as the small sample size. In general, total number of events, not sample number, has relation to the statistical power of Cox regression analysis. Anyway, these discrepancies should be verified by further study. Conflict of interest The author has indicated no financial support. The author has declared that no conflict of interest exists.
References
& Tomoyuki Kawada [email protected] 1
Department of Hygiene and Public Health, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-Ku, Tokyo 113-8602, Japan
1. Muto S, Kawano H, Higashihara E, Narita I, Ubara Y, Matsuzaki T, et al. The effect of tolvaptan on autosomal dominant polycystic kidney disease patients: a subgroup analysis of the Japanese patient subset from TEMPO 3:4 trial. Clin Exp Nephrol. 2015. doi:10. 1007/s10157-015-1086-2. 2. Torres VE, Chapman AB, Devuyst O, Gansevoort RT, Grantham JJ, Higashihara E, et al. Tolvaptan in patients with autosomal dominant polycystic kidney disease. N Engl J Med. 2012;367:2407–18.
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Clin Exp Nephrol 3. Kawada T. Validating GFR estimating samples with clinical outcomes. Am J Kidney Dis. 2014;63:859. 4. Matsuo S, Imai E, Horio M, Yasuda Y, Tomita K, Nitta K, et al. Revised equations for estimated GFR from serum creatinine in Japan. Am J Kidney Dis. 2009;53:982–92.
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5. Horio M, Imai E, Yasuda Y, Watanabe T, Matsuo S. Modification of the CKD epidemiology collaboration (CKD-EPI) equation for Japanese: accuracy and use for population estimates. Am J Kidney Dis. 2010;56:32–8.
LETTER TO THE EDITOR
The effect of tolvaptan on kidney function in patients with autosomal dominant polycystic kidney disease Tomoyuki Kawada1
Received: 10 May 2015 / Accepted: 3 June 2015 Ó Japanese Society of Nephrology 2015
Keywords Estimated glomerular filtration rate Autosomal dominant polycystic kidney disease Tolvaptan Validity To the Editor, I greatly appreciate a subgroup analysis by Muto et al. [1], to evaluate the safety and efficacy of tolvaptan in Japanese autosomal dominant polycystic kidney disease (ADPKD) patients. According to the original report [2], the authors specified the concordance and discrepancy of the results by main and sub-analysis. I have some queries on their study outcome with special emphasis on kidney function by estimated glomerular filtration rate (eGFR), because I recently discussed a validation on several estimating procedures of GFR for Asian population [3]. Muto et al. mentioned that they quoted a reference of eGFR calculation by modified Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation [4], but this paper does not handle with CKD-EPI. As the original report [2] quoted a validation study on CKD-EPI modification for Japanese [5], there is a possibility that Muto et al. made a technical error of citation. Concerning to the eGFR, Muto et al. discussed about the lower eGFR in Japanese ADPKD patients at baseline,
which was compared to the original report, and speculated the reason on the difference of stature between Japanese and multi-ethnic patients. There is a fact that the CKD-EPI study equation presents a lower prevalence of CKD than the prevalence by using equation of Modification of Diet in Renal Disease study in Japan and United States. Taking together, I recommend Muto et al. verifying the equation of eGFR in their study. Finally, the authors used Cox regression analysis to know the efficacy of tolvaptan on four end points, and worsening of kidney function was significantly reduced by tolvaptan treatment with hazard ratio (95 % confidence interval) of 0.17 (0.06–0.49). I suppose that the sole variable is treated in the model [2], and small number of events can keep a valid estimate. But the authors speculated the reason of discrepancy of statistical significance on ADPKD-related composite events and kidney pain between main and sub-analysis as the small sample size. In general, total number of events, not sample number, has relation to the statistical power of Cox regression analysis. Anyway, these discrepancies should be verified by further study. Conflict of interest The author has indicated no financial support. The author has declared that no conflict of interest exists.
References
& Tomoyuki Kawada [email protected] 1
Department of Hygiene and Public Health, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-Ku, Tokyo 113-8602, Japan
1. Muto S, Kawano H, Higashihara E, Narita I, Ubara Y, Matsuzaki T, et al. The effect of tolvaptan on autosomal dominant polycystic kidney disease patients: a subgroup analysis of the Japanese patient subset from TEMPO 3:4 trial. Clin Exp Nephrol. 2015. doi:10. 1007/s10157-015-1086-2. 2. Torres VE, Chapman AB, Devuyst O, Gansevoort RT, Grantham JJ, Higashihara E, et al. Tolvaptan in patients with autosomal dominant polycystic kidney disease. N Engl J Med. 2012;367:2407–18.
123
Clin Exp Nephrol 3. Kawada T. Validating GFR estimating samples with clinical outcomes. Am J Kidney Dis. 2014;63:859. 4. Matsuo S, Imai E, Horio M, Yasuda Y, Tomita K, Nitta K, et al. Revised equations for estimated GFR from serum creatinine in Japan. Am J Kidney Dis. 2009;53:982–92.
123
5. Horio M, Imai E, Yasuda Y, Watanabe T, Matsuo S. Modification of the CKD epidemiology collaboration (CKD-EPI) equation for Japanese: accuracy and use for population estimates. Am J Kidney Dis. 2010;56:32–8.
