*Purpose: Cytomegalovirus (CMV) is the most common infection after solid organ transplantation and is associated with increased morbidity and mortality. CMV prophylaxis is widely considered as standard of care after liver transplantation, and valganciclovir (VGCV) 900 mg daily (adjusted for renal function) is currently the preferred regimen. While effective in preventing CMV infection, this dosing strategy is associated with profound leukopenia, which poses a barrier to optimal immunosuppression management post-transplant and consequently increases risk of rejection. Literature in kidney transplantation has demonstrated that a lower dose of VGCV 450 mg daily (adjusted for renal function) is equally effective in preventing CMV disease and causes less leukopenia. There is a paucity of literature on the use of such reduced dose strategy in liver transplantation. The purpose of this study is to evaluate the safety and efficacy of high-versus low-dose valganciclovir in adult liver transplant recipients.

*Methods: This is a single-center retrospective chart review study of high (D+/R-) and intermediate (R+) risk adult liver transplant recipients who received low-dose valganciclovir (VGCV) 450 mg daily (adjusted for renal function) at our center. Patients were compared to a historical cohort of liver transplant recipients who received high-dose VGCV 900 mg daily (adjusted for renal function). The primary outcome was the incidence of CMV infection or disease within 12 months post-transplantation. Safety outcomes include the incidence of leukopenia at specific time intervals up to 12 months and the need for granulocyte colony stimulating factor (GCSF) at any point while on VGCV therapy.

*Results: Baseline patient demographics and transplant characteristics were found to be comparable across both groups. CMV infection occurred in 13.8% (n=8) and 9% (n=3) in the high-dose and low-dose groups respectively (p=0.302). In the high-dose VGCV group, 75% (6/8) of patients that developed CMV infections were CMV D+/R- and infections mostly occurred after completion of prophylaxis. In the low-dose group, 33% (1/3) of patients were CMV high risk. Patients receiving high-dose VGCV experienced more leukopenia at 1 month post-transplant, than those in the low dose group (5.8 K/uL vs 7.5 K/uL; p = 0.0114). The use of GCSF while on VGCV therapy was also higher in the high- versus low-dose group (7 patients vs 1 patient). There was no difference in acute rejection, resistant CMV infections, biopsy confirmed tissue invasive disease, breakthrough CMV or VGCV duration of therapy. Patient and graft survival outcomes were also similar between groups.

*Conclusions: Low-dose valganciclovir is associated with similar outcomes to high-dose valganciclovir when used for CMV disease prophylaxis in liver transplant recipients. There was a higher use of G-CSF in patients on high-dose valganciclovir.

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