Optimizing cytomegalovirus treatment through therapeutic drug monitoring in a ganciclovir-unresponsive lung transplant recipient.

Ganciclovir and valganciclovir are utilized in the treatment of cytomegalovirus infection and its reactivation following lung transplantation. However, treatment complexity arises due to the development of resistant viruses. Recently, therapeutic drug monitoring of ganciclovir has been studied to enhance dosing strategies for both ganciclovir and valganciclovir. We present a case of a lung transplant recipient who developed cytomegalovirus infection and diarrhea despite valganciclovir prophylaxis. Therapeutic drug monitoring confirmed that the area under the curve of ganciclovir was 67.0 μg h/mL, indicating adequate drug absorption. Although genotypic sequencing tests for antiviral resistance to cytomegalovirus were unavailable at our institution, our therapeutic drug monitoring findings raised suspicion of ganciclovir resistance in the cytomegalovirus. Therefore, the antiviral regimen was modified to foscarnet, leading to prompt cytomegalovirus clearance. Subsequently, foscarnet was replaced with letermovir for secondary prophylaxis. Throughout the treatment, tests for cytomegalovirus DNA and pp65 antigens consistently yielded negative results. This case underscores the value of therapeutic drug monitoring in suspecting potential ganciclovir resistance.