Vincristine-induced adverse events related to body weight in dogs treated for lymphoma

Background: Traditional dosing of chemotherapy drugs based on body surface area may overdose small dogs, leading to an increased frequency of adverse events (AEs). Hypothesis/Objectives: Evaluate the frequency of hematologic and gastrointestinal AEs in dogs with newly diagnosed lymphoma treated with vincristine weighing <= 15 kg in comparison to dogs weighing >15 kg. We hypothesized that dogs weighing <= 15 kg would experience a higher frequency of AEs. Animals: One hundred and thirty-eight dogs with newly diagnosed lymphoma were treated with vincristine. Methods: A multicenter retrospective study reviewing hematologic data and medical record information. Complete blood counts were performed no more than 24 hours before vincristine administration and then between 4 and 8 days post-administration. Data were evaluated using logistic regression or ordinal logistic regression. Results: Thirty-eight dogs weighing <= 15 kg and 100 dogs weighing >15 kg were included. The median vincristine dose for both groups was 0.6 mg/m(2). Seventeen (12.3%) instances of neutropenia occurred with no significant difference in overall frequency or grade between groups. Thirty initially asymptomatic substage A dogs (29.4%) experienced gastrointestinal AEs. Because of the widespread use of gastrointestinal supportive care medications, statistical comparison between groups could not be performed. Seven instances of hospitalization occurred (5.0%) and the risk of hospitalization did not differ significantly between groups (P = .37). Conclusions and Clinical Importance: Vincristine dosed at <= 0.6 mg/m(2) does not increase the risk of hematologic AEs in dogs weighing <= 15 kg.