Polyomavirus-associated nephropathy: update of clinical management in kidney transplant patients.

Over the last decade, polyomavirus-associated nephropathy (PVAN) has occurred with increasing frequency after renal transplantation, leading to significant renal dysfunction and graft loss. More than 95% of all cases are caused by the human polyomavirus type 1 called the BK virus. The primary treatment for PVAN is immunosuppression reduction, which must be carefully balanced against increased risks of rejection. Although no validated protocols exist, a first step commonly involves reduction of calcineurin inhibitors with antiproliferative agents by more than one-third, e.g., reaching trough levels of tacrolimus <6 ng/mL, of cyclosporine <150 ng/mL, dosing of mycophenolate mofetil to <1 g/day, and azathioprine <75 mg/day. When rejection is diagnosed together with PVAN, a transient pulse treatment is recommended before subsequent reduction in immunosuppression. No antiviral treatments for PVAN have been approved by the United States Food and Drug Administration. The antiviral drug cidofovir has shown in vitro activity against murine polyomaviruses, and has been used in some patients in lower doses in an effort to minimize the nephrotoxic effects of cidofovir while treating PVAN. Small series of PVAN patients treated with leflunomide, intravenous immune globulin therapy, and fluoroquinolones have also been reported recently.