Cytomegalovirus causes morbidity and mortality, especially in immunocompromised patients, and is treated with (val)ganciclovir. Therapeutic drug monitoring of ganciclovir is often performed; however, clinically established target trough levels corresponding to efficacy are lacking. In 2021, our clinic increased the target trough level for ganciclovir from 1 to 2 mg/L to 2–4 mg/L. This study aims to compare both target trough levels in efficacy, toxicity, and occurrence of resistance.

A retrospective cohort study was performed in adult solid organ recipients treated for cytomegalovirus infection with (val)ganciclovir. Clinical efficacy was defined as the absence of treatment failure, defined as > 1 log10 increase in viral load within 2 weeks of treatment initiation, therapy switch to foscarnet, and/or request for resistance analysis.

A total of 46 patients were involved in the study, with 200 ganciclovir trough levels obtained. The composite endpoint was recorded in 23 (69.7%) and 10 (76.9%) patients in the 1–2 mg/L and the 2–4 mg/L group, respectively (P = 0.18). No association was found between ganciclovir trough levels and the composite endpoint (P = 1.0). However, a correlation was found between ganciclovir trough levels and the occurrence of lymphopenia (P = 0.02).

Our study could not establish a difference in clinical efficacy or toxicity between target trough levels of 1–2 mg/L or 2–4 mg/L because of the lack of clinical differences between the compared groups. However, a correlation was found between ganciclovir trough levels and lymphopenia, which warrants further investigation.