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Neutrophil Count Cutoff for Antimicrobial Prophylaxis in Dogs Treated for Cancer

R. Darren Wood, DVM, DVSc, DACVP (Clinical Pathology), University of Guelph, Guelph, Ontario, Canada


|April/May 2021

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In the literature

Bisson JL, Fournier Q, Johnston E, Handel I, Bavcar S. Evaluation of a 0.75 × 109/L absolute neutrophil count cut-off for antimicrobial prophylaxis in canine cancer chemotherapy patients. Vet Comp Oncol. 2020;18(3):258-268.


Dogs being treated for cancer with chemotherapeutic agents are at risk for bone marrow suppression, which may also put them at risk for secondary bacterial infections, thereby complicating further management and potentially decreasing likelihood of response to therapy. There is controversy regarding how severe neutropenia must become before risk for infection substantially increases. Appropriate use of antimicrobials should include consideration of clinical requirements and respect toward stewardship to prevent further antibiotic resistance.

This study had 2 objectives. The first was to compare the incidence of postnadir febrile neutropenia and nonhematologic toxicity in dogs with absolute neutrophil counts <0.75 x 109/L that were receiving prophylactic antimicrobials with dogs with absolute neutrophil counts above this threshold that were not receiving antimicrobials. The second objective was to compare the proportion of chemotherapy administrations that would require antimicrobial prophylaxis if various absolute neutrophil count cutoffs were used.

Medical records of 181 dogs were reviewed, and no significant difference in the incidence of febrile neutropenia and nonhematologic toxicity was found between dogs that did and did not receive antimicrobials. In fact, there was a lower incidence of nonhematologic toxicity in those dogs not receiving antimicrobials. These findings suggest that an absolute neutrophil count cutoff of <0.75 x 109/L was well-tolerated for clinically well patients undergoing hematologic assessment after chemotherapy, even when accounting for risk factors that could cause predisposition to secondary infections. Of 586 chemotherapy administrations, only 4 incidences of postnadir febrile neutropenia after treatment occurred.

Antimicrobial resistance is a global concern, and prudent use of these medications is increasingly important. Reduction of prophylactic antimicrobial use when possible is a key component to reducing further resistance. In a previous survey,1 96% of clinicians prescribing prophylactic antimicrobials used a cutoff of <1 x 109/L. The current study suggests the threshold can safely be decreased to <0.75 x 109/L in most patients.

Clinician decision about whether to use prophylactic antimicrobials in cancer patients receiving chemotherapy is key. There may be concern that secondary infections can occur, but with astute physical assessment by the pet owner and clinician and lack of dangerous decrease of postnadir absolute neutrophil counts, it appears that most patients do not develop febrile neutropenia.


Key pearls to put into practice:


An absolute neutrophil count cutoff of <0.75 x 109/L (<750/µL) was tolerated in clinically well patients undergoing hematologic assessment after chemotherapy.



There was no significant difference between the 2 groups (those receiving and not receiving antibiotics) in the incidence of febrile neutropenia and nonhematologic toxicity after treatment.



Opportunities to minimize the use of prophylactic antimicrobials should be considered when possible to contribute to decreasing global antimicrobial resistance.


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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