Proteinuria as a surrogate end point--more data are needed

Surrogate end points have the potential to facilitate drug development because effects on surrogate end points can sometimes be demonstrated more rapidly and in smaller studies than can effects on clinical outcomes of interest. Proteinuria has been repeatedly proposed as a surrogate end point for renal outcomes in drug development; however, the FDA has generally not accepted effects on proteinuria as evidence of a drug's effectiveness. Proteinuria is an early marker of some kidney diseases and increases in proteinuria can predict risk of disease progression. Whether or not treatment effects on proteinuria can reliably predict treatment effects on renal outcomes is not known. Nevertheless, it may be reasonable to use effects on proteinuria as a basis for accelerated approval of a drug if certain conditions are met. Approval under this pathway carries with it a requirement to complete a study after drug approval that verifies the anticipated treatment benefit.