Design of human trials in progressive renal failure

Summary: Future studies aimed at testing therapies to prevent progression of renal failure have much to learn from the past successful and unsuccessful attempts. Given the insensitivity of all other methods, the proper index of renal function for study of progression of renal failure should be radioisotope glomerular filtration marker clearance. Randomized prospective controlled studies are required, and statistical analysis should be designed to allow consideration for patient drop out and covariants. Since compensatory mechanisms come into place as soon as there is any nephron damage, more attention should be paid to studying the progression of renal failure from a normal glomerular filtration rate (GFR) until there is an elevated plasma creatinine level. This suggestion is supported by four under-lying concepts: (i) overall GFR does not fall until about 23% of nephrons are destroyed; (ii) if progression is multifactorial, the later in the progress the more likely that more factors are present to confound issues; (iii) this may allow study of greater patient numbers, since patients who have had renal biopsy or ultrasound diagnosis can be entered before the plasma creatinine is abnormal; (iv) in early stages of disease, issues of concurrent treatment may be less difficult (e.g. diet, phosphate control, hypertension). With diabetes, prognosis and progression has been related to proteinuria. In non-diabetic disease proteinuria has been related to progression, but the effect of alleviation of proteinuria on prognosis has not been intensively studied. There is a need to study the relationships between proteinuria and progression, particularly in early renal disease. At present most therapies are based upon observations in the partially ablated rat model. Other animal models should be developed, and the details of early mechanisms in the rat further clarified. Since we believe progression is likely to be multifactorial in pathogenesis, combination therapies may be required to optimally reduce progression.