Renal function and tubular phosphate handling in long-term cyclosporine- and tacrolimus-based immunosuppression in kidney transplantation.

The aim of the study was to assess impaired tubular phosphate reabsorption and renal function among patients on cyclosporine- or tacrolimus-based immunosuppression for 2 years after kidney transplantation. Among 60 cadaveric kidney allograft recipients observed for 48 months, 40 received cyclosporine, azathioprine, and prednisone (group A and B). Group C consisted of 20 patients receiving tacrolimus with steroid withdrawal at 3 months after transplantation. Renal function and calcium-phosphate metabolism-iPTH, 25-OHD, 1,25(OH)(2)D concentration, phosphate reabsorption (TRP; mmol/L), and tubular maximum phosphate reabsorption per glomerular filtration rate (TmPO(4)/GFR; mmol/L)-were assessed at 1, 6, 12, 18, and 24 months (groups A and C) or 24, 30, 36, 42, and 48 months (group B). Renal function after 24 months of observation was significantly better among tacrolimus-treated patients (serum creatinine concentration mumol/L; C: 94.6 +/- 16.8 vs A: 110.5 +/- 22.1 vs B: 121.1 +/- 30.9; P < .05). Among tacrolimus-treated recipients, TRP and TmPO(4)/GFR remained within normal values during the whole observation period. In groups A and B, TRP improved during the first year of observation; after 2 years it reached values observed in group C (TRP: A: 0.67 +/- 0.1; B: 0.72 +/- 0.13; C: 0.76 +/- 0.07; P = NS), whereas TmPO(4)/GFR remained low in group A after 2 years (A: 0.78 +/- 0.19; B: 0.91 +/- 0.25; C: 0.94 +/- 0.15; P < .05). Tacrolimus-treated patients exhibit significantly faster recovery from tubular phosphate reabsorption impairment compared with cyclosporine-treated recipients. Tacrolimus-based immunosuppression led to better kidney allograft function during 2-year observation.