Vincristine Induced Adverse Effects in Lymphoma Bearing Dogs With Asymptomatic Neutropenia at the Time of Drug Administration.

Vincristine sulphate, a microtubule inhibitor, is used extensively in veterinary oncology for treating lymphoma. Neutropenia during multiagent protocols is a common reason for treatment delay and reduced dose intensity. This study evaluated toxicities associated with treating systemically well neutropenic lymphoma patients with vincristine. Lymphoma patients undergoing CHOP were evaluated retrospectively for instances of vincristine administration when absolute neutrophil counts (ANC) were 1.5 × 10⁹/L or below. Instances of vincristine administration when ANC was equal to or less than 1.5 × 10⁹/L were compared to vincristine administration where ANC was greater than 1.5 × 10⁹/L in the same patient. Univariate and multivariate modelling compared VCOG-CTCAE v1.1 grading of vomiting, diarrhoea, anorexia and 7-day neutrophil nadir between groups. The median dose of vincristine administered was 0.7 mg/m² for both study groups. A total of 112 doses of vincristine were administered to neutropenic patients (grade 2 n: 76, grade 3 n: 26, and grade 4 n: 10). These were compared to 223 doses of vincristine administered to the same patients when ANC was above 1.5 × 10⁹/L. Neutropenic administration was most prevalent 7 days following cyclophosphamide administration. Day 7 post-administration neutropenia was more prevalent in patients with ANC greater than 1.5 × 10⁹/L at the time of vincristine administration (neutropenic 9%; non-neutropenic 18%). Relative risk of 7-day neutropenia, vomiting, diarrhoea, and anorexia was similar between groups on multivariate analysis. Patients with lymphoma who receive vincristine when ANC is 1.5 × 10⁹/L or below are at no greater risk of adverse effects than the same patient who receives vincristine when neutrophil counts are greater than 1.5 × 10⁹/L.