Opportunistic CMV viremia (primary infection or reactivation) is usually managed by taking prophylactic medication for both adult and pediatric kidney transplant patients. Most hospitals prescribe valganciclovir for this purpose but valacyclovir has also been used. The most unfavorable side effect of valganciclovir is bone marrow suppression which can be troublesome for kidney transplant patients who are already immunosuppressed. We aim to assess the non-inferiority of valacyclovir compared with valganciclovir in this study.

CMV viremia and EBV viremia are commonly seen in immunosuppressed kidney transplant recipients. These patients are at highest risk for CMV or EBV viremia early post-transplant or during a period of heightened immunosuppressive regimen to treat acute rejection. CMV viremia could be asymptomatic when the viral load is low, but if uncontrolled, it could lead to severe organ-invasive disease. On the other hand, EBV viremia, though usually not an immediate threat to allograft, harbors risk for post-transplant lymphoproliferative disease (PTLD).Therefore, most transplant centers adopt regular surveillance as well as following certain protocols of antiviral prophylaxis, using valganciclovir specifically against CMV viremia.

Valganciclovir is highly effective as prophylaxis for CMV viremia, but it is also known for its side effects such as myelosuppression and nephrotoxicity. Valacyclovir, though better known for its therapeutic effect for herpes simplex virus, is emerging as an alternative to valganciclovir since some retrospective studies showing its comparative efficacy in CMV prophylaxis. Valacyclovir has favorable side effect profile, and is less expensive. It may also reduce EBV viral shedding in oropharynx, though there's no evidence showing its efficacy in preventing EBV viremia or even PTLD in kidney transplant patients. Given that there are scarce prospective studies comparing these two medications in kidney transplant recipients, our study aims to assess the non-inferiority of valacyclovir compared with valganciclovir as prophylaxis for CMV viremia and investigate its non-inferiority for EBV viremia. We will include both pediatric and adult kidney transplant recipients who received kidney transplant less than 5 years prior to study participation and the patients will be stratified based on their age, years post-transplant, and CMV risk status. Serum viral load and other possible side effects will be monitored during their clinic visits for at least 2 years. The findings from this study will be informative for the design and power calculations for a larger multicenter non-inferiority trial. If valacyclovir is indeed non-inferior to valgancyclovir in both CMV viremia and EBV viremia, utilizing this medication in our post-kidney transplant protocol may help reduce side effect burden and potentially save substantial healthcare cost.

Inclusion Criteria:

• Age at least 3 years of age
• Patients who are about to receive or just received kidney transplantation within the past 2 weeks before the date of screening.
• Will be receiving prophylactic antiviral therapy against CMV and/or EBV per discretion of transplant surgeon
• No active CMV or EBV viremia (as defined by detectable viral load PCR) at the time of screening.
• Ability and willingness of the patient (or parent/legal guardian for minors) to provide informed consent and comply with study procedures.

Exclusion Criteria:

• Severe co-morbidities that would preclude safe participation as judged by the transplant surgeon
• Pregnancy (valganciclovir is likely teratogenic)
• Known allergy to both valacyclovir and valganciclovir