Maintenance Immunosuppressive Agents as Risk Factors for BK Virus Nephropathy: A Case-Control Study

Background. The specific role of different immunosuppressive agents as risk factors for BK virus nephropathy (BKN) has not been well studied. Methods. In this case-control study, we examined the association of tacrolimus (TAC), mycophenolate mofetil (MMF), and prednisone with BKN in renal allograft recipients transplanted between 1997 and 2004 at our center who underwent biopsies for allograft dysfunction. Drug levels or doses were recorded during the 3 months before the index biopsy. Random effects logistic modeling was used for data analysis. Results. There were 33 cases with BKN, biopsied at 16.4 +/- 2.8 months and 66 matched controls with biopsies at 21.5 +/- 2.1 months posttransplant (P = 0.16). After adjusting for sex, race, retransplant status, diabetes, donor source, and induction agent, TAC blood level was associated with increased risk of BKN (odds ratio [OR] 1.3, 95% confidence interval [CI] 1.02-1.7, P = 0.03), whereas MMF dose was not (OR 1.0, 95% Cl 0.99-1.0, P = 0.2). Moreover, prednisone dose was also found to be a significant risk factor for BKN (OR 1.22, 95% CI 1.04-1.4, P = 0.02). Conclusions. The results of this study show that BKN is associated with TAC level and prednisone dose and not with MMF dose. This suggests that reducing TAC and prednisone dose and maintaining MMF may be a more appropriate initial approach for the treatment of BKN. Further studies are needed to compare the efficacy and safety of this approach with the currently recommended one.