Abstract: Background: Lomustine (CCNU) can cause severe neutropenia in dogs, increasing the risk of life-threatening secondary bacterial infections. Prophylactic antibiotics (pAB) may decrease the incidence of bacterial infection but contribute to growing antimicrobial resistance. To improve judicious use of pAB, it is important to define their role in improving patient care.
Hypothesis/Objectives: Similar rates of neutropenia-related adverse events occur in dogs when pAB are given with CCNU at only the first treatment compared to pAB given with each treatment.
Animals: Pet dogs treated with CCNU by an oncology service.
Methods: Medical records were retrospectively queried between 2019-2023 for dogs with lymphoma or histiocytic sarcoma treated with CCNU. Use of pAB, CCNU dosage, grade 4 neutropenia, and febrile and hospitalization events were compared between dogs receiving pAB with the first cycle or with 2 cycles using Fisher’s exact test.
Results: Seventy-eight CCNU treatments in 39 dogs were evaluated. Twenty-one dogs received pAB with the first CCNU treatment only (Group 1); 18 dogs received pAB with both treatments (Group 2). Five treatments in group 1 (12%) and 11 in group 2 (30%) resulted in grade 4 neutropenia (p=0.052). Six treatments in group 1 (14%) and 15 in group 2 (42%) resulted in dose reduction (p=0.010). Febrile events occurred in 19% of treatments without pAB compared to 3.5% with pAB (p=0.042).
Conclusions and clinical importance: The timing and role of pAB in dogs undergoing CCNU treatment needs to be better defined. The advantages must be weighed against potential disadvantages of antibiotic resistance.
