Conversion from mycophenolate mofetil to mizoribine for patients with positive polyomavirus type BK in urine

It is known that administration of mycophenolate mofetile (MMF) is associated with BK virus (BKV) nephropathy in renal transplant recipients. To determine any inhibitory effect of mizoribine for BKV, seven patients with positive BKV in their urine who took MMF as immunosuppressive therapy were evaluated after MMF was changed to mizoribine. Baseline BKV DNA in urine, which ranged from 2.2 x 10(2) to 5.5 x 10(6) copies per milliliter, decreased in all cases (mean = 1.9 x 10(-1) times; median 2.8 x 10(-3) times). Four cases turned negative within 6 months and one within 12 months. No acute rejection or deterioration of graft function occurred during the administration of mizoribine. An inhibitory effect of mizoribine on BKV was suggested.