Comparison of interpatient and intrapatient variability in doxorubicin exposure using a validated limited sampling model in dogs with cancer.

Background: Doxorubicin (DOX) is an anthracycline chemotherapeutic used for many canine malignancies, and its adverse event (AE) profile has been well-described in dogs. A limited sampling (LS) pharmacokinetic model was recently developed in canine patients to predict hematologic exposure to DOX. The primary goal of this study was to evaluate within-patient and between-patient variability in DOX exposure over three consecutive doses using the LS model. A secondary goal was to determine if there is a correlation between DOX exposure and gastrointestinal (GI) AEs utilizing a standardized owner questionnaire. Methods: We performed a prospective evaluation of DOX exposure in seven tumor-bearing dogs across three cycles of treatment and compared the coefficient of variation (%CV) of the between- and within-patient exposures. Results: This data set corroborated the ability of the DOX LS model to predict absolute neutrophil count for patients whose absolute neutrophil counts are lower at seven days compared to baseline. Dose normalized within-patient variability (4.7%) was significantly lower ( Conclusions: Together, these data suggest wide interpatient variability in dose-normalized DOX exposure but much more consistent exposure within an individual patient across treatment cycles. Future studies can attempt to target specific DOX exposures and absolute neutrophil counts to assess if DOX dosing can be personalized to increase efficacy and decrease GI AEs. Supplementary Information: The online version contains supplementary material available at 10.1186/s44356-025-00038-z.