AbstractBackgroundValganciclovir is the first‐line agent for Cytomegalovirus prophylaxis after lung transplantation. However, its use is associated with a relatively high risk of hematological toxicity. This study aimed to investigate the relationship between trough ganciclovir concentration and hematologic toxicity in lung transplantation patients receiving valganciclovir prophylaxis, and identify factors that affect ganciclovir pharmacokinetics in this population.MethodsThis prospective observational study included 24 lung transplant patients receiving valganciclovir prophylaxis. The cutoff value of trough ganciclovir concentration was estimated using receiver operating characteristic analysis in leukopenia grade 3 and higher. Population pharmacokinetic analysis was performed using a nonlinear mixed‐effects modeling program.ResultsThe trough ganciclovir concentration was significantly higher in the group with leukopenia grades 3 or higher than in the group with grades less than or equal to 2 (1605.7 ± 860.1 ng/mL [n = 3] vs. 380.5 ± 175.8 ng/mL (n = 21), p < .001). The cutoff value of trough ganciclovir concentration for predicting greater than or equal to grade 3 leukopenia was estimated as 872.0 ng/mL. Creatinine clearance and lung re‐transplantation were found to have a significant impact on the total body clearance of valganciclovir. Ganciclovir clearance was decreased in patients with reduced creatine clearance or re‐transplantation.ConclusionThese results suggest that higher ganciclovir trough concentrations are associated with an increased risk of leukopenia grade 3 or higher, and that creatinine clearance and lung re‐transplantation affected the pharmacokinetics of ganciclovir. image