to leflunomide. There are no dosing guidelines for leflunomide in BKVAN. Patient to patient variability has made dosing and monitoring of leflunomide extremely difficult. Study of 26 and 17 patients were dosed between 20 mg/day and 60 mg/day with trough levels of 50—100 µg/ml. Failure was seen in patients with leflunomide plasma levels < 40 µg/ml. One study of 21 patients found that low levels (< 40 µg/ml) and high levels (> 40 µg/ml) had similar effects on the rate of viral clearance. Those with higher levels had more adverse events (hematologic, hepatic). In the study by Teschner et al., dosages and drug concentration showed no correlation with substantial variation from person to person. In the Teschner study, low drug concentrations were associated with decrease in viral load. This makes it difficult to determine whether or not reduction of viral load or addition of leflunomide was the cause for viral clearance. Other treatment options Quinolone antibiotics: Ciprofloxacin (Cipro) was shown to significantly lower viral loads but no data on survival and graft loss exist. Intravenous immunoglobulin (IVIG) has use in the treatment of infection and allograft rejection – hard to distinguish Cidofovir has limited data and is highly nephrotoxic. History The BK virus was first isolated in 1971 from the urine of a renal transplant patient, initials B.K. The BK virus is similar to another virus called the JC virus (JCV), since their genomes share 75% sequence similarity. Both of these viruses can be identified and differentiated from each other by carrying out serological tests using specific antibodies or by using a PCR-based genotyping approach. See also Decoy cells Low-dose naltrexone References External links Overview of the BK virus MicrobiologyBytes: Polyomaviruses Polyomaviridae