The BK virus, a DNA virus from the Polyomavirus group, represents an opportunistic infection of immunosuppressed transplant recipients. Though the virus was discovered approximately 40 years ago, the emergence of BK virus nephropathy since 1995 onwards, with associated high graft loss rates, has revolutionized renal transplantation medicine. Kidney transplant professionals realized that the consequences of over-immunosuppression were as severe as the consequences of under-immunosuppression and we entered the era of immunosuppressive minimization. Despite this recognition, the optimal testing type for BK virus infections and frequency of testing are hotly debated. Similarly, optimal treatment strategies remain sources of intense controversy. The authors review the current strategies of screening, diagnosis, and possible treatment, and also review the amount and quality of evidence in favor or against. Similarities and differences between cytomegalovirus, Epstein-Barr virus, and BV virus, the three major viral infections in kidney transplantation, are highlighted.

A generic version of tacrolimus was approved for use in the USA in August 2009. These narrow therapeutic index generics are tested for bioequivalence only in adults. No data are available on generic tacrolimus levels in children with allografts. Four patients with stable renal allografts in our pediatric program were inadvertently switched to generic tacrolimus. We retrospectively analyzed pre- and post-switch trough tacrolimus and serum creatinine levels. Twelve-h trough tacrolimus levels (mean ± s.e.) were (i) patient 1 (12-yr-old girl): 7.0 ± 0.69 and 9.7 ± 3.5 (p =NS); (ii) patient 2 (eight-yr-old boy): 4.7 ± 0.68 and 3.4 ± 0.84 (p = 0.04); (iii) patient 3 (22-yr-old woman): 6.8 ± 0.17 and 6.6 ± 0.4 (p = NS); (iv) patient 4 (20-yr-old woman): 5.4 ± 0.25 and 4.9 ± 1.4 (p = NS). Creatinine levels were similar pre- and post-switch (eGFR > 75 mL/min/1.73 m²) in the first three. Patient 4 experienced a biopsy proven acute rejection immediately after switching. Mean creatinine rose from 1.15 ± 0.05 to 2.168 ± 0.07 after switch (p < 0.001). Given our mixed picture with the early data, we suggest careful monitoring of pediatric patients who get switched to generic tacrolimus.