Population Pharmacokinetics of Ganciclovir in Critically Ill Patients

Background: The pharmacokinetic (PK) data of ganciclovir (GCV), a first-line antiviral treatment for cytomegalovirus infections, in critically ill patients are limited. This study aimed at characterizing GCV population PK and interindividual variability (IIV) in intensive care unit (ICU) patients. Secondary objectives were to identify patient characteristics responsible for IIV and simulate GCV exposure for different dosing regimens. Method: In this retrospective observational study, clinical data and serum GCV levels were collected from ICU patients on intravenous GCV. PK modeling, covariate analyses, and explorative Monte Carlo dosing simulations (MCS) were performed using nonlinear mixed-effects modeling. Bootstrap and visual predictive checks were used to determine model adequacy. Results: In total, 128 GCV measurements were obtained from 34 patients. GCV PK conformed to a 1-compartment model with first-order elimination. After multivariate analyses, only the estimated glomerular filtration rate calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula (P < 0.001) was included as a covariate. In the final model, the estimated clearance (CL) and volume of distribution (V1) were 2.3 L/h and 42 L, respectively, for a patient with the median CKD-EPI of the population (65 mL/min per 1.73 m2). The association between CKD-EPI and CL decreased the residual variability from 0.56 to 0.43 and V1-IIV from 114% to 80%, whereas CL-IIV changed from 43% to 47%. MCS revealed that a substantial number of patients may not achieve the GCV PK/pharmacodynamic target trough level (>1.5 mg/L) when administering the label-recommended dose reductions for patients with CKD-EPI <50 mL/min. Conclusions: A large IIV was observed in GCV PK among ICU patients. CKD-EPI could partially explain the IIV, although a large part of the variability remains unclear. MCS suggested that recommended dose reductions for CKD-EPI <50 mL/min may lead to subtherapeutic plasma GCV levels in these patients.