MICROVASCULAR CHANGES IN RENAL-ALLOGRAFTS ASSOCIATED WITH FK506 (TACROLIMUS) THERAPY

FK506 (Tacrolimus) recently has been shown to be an effective immunosu ppressant after renal transplantation. It is associated with less hype rtension, hypercholesterolemia and steroid use compared with cyclospor ine. We report 10 patients on FK506 who showed fibrin thrombi within t he glomerular capillaries and/or arterioles at renal allograft biopsy. These biopsies were generally per formed to assess increasing serum c reatinine levels; laboratory evidence of hemolytic uremic syndrome was present in one instance. Plasma or whole blood FK506 levels were elev ated in eight of 10 cases. Reduction of immunosuppression led to clini cal improvement or biopsy-proven resolution of thrombi in all cases. T hese observations suggest that FK506 may occasionally produce microvas cular changes in the renal allograft. The estimated incidence of this occurrence (1%) is comparable with that reported with cyclosporine (3% ).