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Background: There is interest in surrogate end points for clinical trials of chronic kidney disease progression because currently established end points-end-stage renal disease (ESRD) and doubling of serum creatinine level-are late events, requiring large clinical trials with long follow-up. Doubling of serum creatinine level is equivalent to a 57% decline in estimated glomerular filtration rate (eGFR). We evaluated type 1 error and required sample size for clinical trials using surrogate end points based on lesser eGFR declines., Study Design: Simulation study., Setting & Participants: Simulations evaluating 3,060 scenarios representative of 19 treatment comparisons in 13 chronic kidney disease clinical trials., Index Tests: Surrogate end points defined as composite end points based on ESRD and either 30% or 40% eGFR declines., Reference Test: Clinical outcome (ESRD) for type 1 error. Established end point (composite of ESRD and 57% eGFR decline) for required sample size., Results: Use of the 40% versus 57% eGFR decline end point consistently led to a reduction in sample size > 20% while maintaining risk for type 1 error < 10% in the presence of a small acute effect (<1.25mL/min/1.73m(2)) for: (1) 2-, 3-, or 5-year trials with a high mean baseline eGFR (67.5mL/min/1.73m(2)), and (2) 2-year trials with an intermediate mean baseline eGFR (42.5mL/min/1.73m(2)). Use of the 30% versus the 40% eGFR decline end point often led to moderately larger reductions in sample size in the absence of an acute effect, but not in the presence of acute effects., Limitations: The complexity of eGFR trajectories prevented evaluation of all scenarios for clinical trials., Conclusions: Use of end points based on 30% or 40% eGFR declines is an appropriate strategy to reduce sample size in certain situations. However, risk for type 1 error is increased in the presence of acute effects, particularly for 30% eGFR declines. The decision to use these end points should be made after thorough evaluation of their expected performance under the conditions of specific clinical trials., (Copyright © 2014 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Background: There is increased interest in using alternative end points for trials of kidney disease progression. The currently established end points of end-stage renal disease and doubling of serum creatinine level, equivalent to a 57% decline in estimated glomerular filtration rate (eGFR), are late events in chronic kidney disease (CKD), requiring large clinical trials with long follow-up. As part of a comprehensive evaluation of lesser declines in eGFR as alternative end points, we describe the consistency of treatment effects of intervention on the alternative and established end points in past trials., Study Design: Diagnostic test study., Setting & Population: 9,488 participants from 37 randomized controlled trials of CKD progression across 5 intervention types., Index Test: Alternative end points including percentage change in eGFR from baseline (20%, 30%, 40%, and 57%) throughout study duration and to 12, 18, and 24 months. eGFR change confirmed versus nonconfirmed at the next visit., Reference Test: The historically established end point of time to composite of treated kidney failure (end-stage renal disease), untreated kidney failure (GFR<15mL/min/1.73m(2)), or doubling of serum creatinine level throughout study duration., Results: Over a median of 3.62 years' follow-up, there were 3,070 established end points. Compared to the established end point, the number of alternative end points was greater for smaller versus larger declines in eGFR and longer versus shorter follow-up intervals. There was a general trend toward attenuation of the treatment effect with end points defined by a lesser eGFR decline, with greater attenuation with nonconfirmed end points, except for the low-protein-diet intervention, for which a stronger treatment effect was observed. The ratio (95% credible interval) of the HR for the alternative to established end point for the 5 intervention types ranged from 0.91 (0.64-1.43) to 1.12 (0.89-1.40) for 40% decline and from 0.88 (0.63-1.39) to 1.15 (0.88-1.54) for 30% decline for the overall study duration, indicating consistency of treatment effects., Limitations: Limited variety of interventions tested and low statistical power for many CKD clinical trials., Conclusions: These results provide some support for the use of lesser eGFR declines as a surrogate end point, with stronger support for the 40% than 30% decline., (Copyright © 2014 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Background: The currently established end points for clinical trials of progression of chronic kidney disease (CKD) are end-stage renal disease and doubling of serum creatinine level, which approximates a 57% decline in estimated glomerular filtration rate (eGFR). There is increased interest in using alternative end points in clinical trials to shorten trial duration and reduce sample size. As part of an evaluation of using lesser declines in GFR as alternative end points, we examined the associations of various levels of eGFR decline with the subsequent development of established end points and assess the consistency of alternate levels of eGFR decline across varying clinical manifestations of kidney disease and interventions., Study Design: Observational analysis of randomized controlled trials., Setting & Participants: 9,488 participants in 37 randomized controlled trials in CKD., Predictor: Alternative end points, defined as 30% and 40% declines in eGFR from baseline to month 12. Effect modification by baseline eGFR, proteinuria, cause of disease, and interventions., Outcomes: Established end point, defined as end-stage renal disease, eGFR<15mL/min/1.73m(2), or doubling of serum creatinine level., Results: From baseline to 12 months, 16.1% and 7.8% of participants had eGFR declines of ≥30% or ≥40%, respectively. Over a median follow-up of 2.0 (IQR, 1.2-3.1) years after the 12-month baseline period, 2,661 established end points were observed. A strong linear association was observed between eGFR decline and subsequent established end points. HRs for the established end point for 30% and 40% decreases in eGFR compared to a 0% decline were 9.6 (95% CI, 7.3-12.6) and 20.3 (95% CI, 14.1-29.3), respectively. The associations were consistent regardless of baseline eGFR, proteinuria, causes of disease, and interventions., Limitations: Observational study subject to residual confounding., Conclusions: The strong associations between lesser declines in eGFR and the subsequent development of established end points were consistent across different clinical characteristics of kidney disease and interventions and support implementation of alternative end points in clinical trials of CKD progression., (Copyright © 2014 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

The US Food and Drug Administration currently accepts halving of glomerular filtration rate (GFR), assessed as doubling of serum creatinine level, as a surrogate end point for the development of kidney failure in clinical trials of kidney disease progression. A doubling of serum creatinine level generally is a late event in chronic kidney disease (CKD); thus, there is great interest in considering alternative end points for clinical trials to shorten their duration, reduce sample size, and extend their conduct to patients with earlier stages of CKD. However, the relationship between lesser declines in GFR and the subsequent development of kidney failure has not been well characterized. The National Kidney Foundation and Food and Drug Administration sponsored a scientific workshop to critically examine available data to determine whether alternative GFR-based end points have sufficiently strong relationships with important clinical outcomes of CKD to be used in clinical trials. Based on a series of meta-analyses of cohorts and clinical trials and simulations of trial designs and analytic methods, the workshop concluded that a confirmed decline in estimated GFR of 30% over 2 to 3 years may be an acceptable surrogate end point in some circumstances, but the pattern of treatment effects on GFR must be examined, specifically acute effects on estimated GFR. An estimated GFR decline of 40% may be more broadly acceptable than a 30% decline across a wider range of baseline GFRs and patterns of treatment effects on GFR. However, there are other circumstances in which these end points could lead to a reduction in statistical power or erroneous conclusions regarding benefits or harms of interventions. We encourage careful consideration of these alternative end points in the design of future clinical trials., (Copyright © 2014 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)