Acute alterations in GFR can occur following the start of therapies aimed at slowing the course of CKD. The acute alterations make interpreting long-term therapy effects more difficult. For a study, researchers conducted a meta-analysis of 53 randomized clinical trials for CKD progression, enrolling 56,413 participants with at least one estimated GFR measurement by 6 months after randomization, to assess the magnitude and consistency of acute effects in randomized clinical trials and to investigate factors that may influence them. They characterized acute treatment effects as the mean difference in GFR slope between randomized groups from baseline to 3 months. They used univariable and multivariable metaregression to see how intervention type, disease status, baseline GFR, and albuminuria affected the size of acute effects. 

Over 3 months, the mean acute impact was 0.21 ml/min per 1.73 m^2 (95% CI, -0.63 to 0.22), with significant heterogeneity between treatments (95% coverage interval across trials, -2.50 to +2.08 ml/min per 1.73 m2). They found negative average acute effects in renin-angiotensin system blockage, blood pressure reduction, and sodium-glucose cotransporter 2 inhibitor trials, but good acute effects in immunosuppressive drug trials. In studies with a greater mean baseline GFR, the unfavorable acute effects were more severe.

The amplitude and consistency of acute GFR effects varied among therapies and are greater with higher baseline GFR. Understanding the origin and severity of acute effects can aid in the design of appropriate randomized clinical trials monitoring disease progression in CKD.