Development and Validation of a Liquid Chromatograph–Tandem Mass Spectrometry Method for Quantifying Ganciclovir in Dried Blood Spots for Therapeutic Drug Monitoring

Valganciclovir (VGCV) is the first-line drug for preemptive therapy of cytomegalovirus (CMV) infection. However, even at standard doses, plasma concentrations of the active metabolite ganciclovir (GCV) show substantial inter-individual variability. To ensure therapeutic efficacy and minimize adverse effects, therapeutic drug monitoring (TDM) based on the area under the concentration-time curve (AUC) is essential. Yet, conventional TDM via venous blood sampling is invasive and unsuitable for frequent monitoring. In this study, we aimed to develop a simple and minimally invasive method for GCV quantification using dried blood spots (DBS) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method demonstrated a good linearity over a concentration range of 0.25-16 μg/mL and satisfied the validation criteria for accuracy and precision. It showed acceptable stability for up to 7 days under refrigerated conditions. Methanol was identified as the optimal extraction solvent, allowing for a simplified sample pretreatment without the need for ultrasonic processing. While hematocrit levels affected spot size and quantification accuracy, reliable measurements were obtained within the 30%-50% hematocrit range. The established DBS-based LC-MS/MS method provides a promising, minimally invasive approach for TDM of GCV in the management of CMV infections.