Evaluation of a 0.75 X 109 /L absolute neutrophil count cut-off for antimicrobial prophylaxis in canine cancer chemotherapy patients

Absolute neutrophil count (ANC) cut-offs for antimicrobial prophylaxis in veterinary cancer chemotherapy patients are empirical and vary between institutions. Evidence based cut-offs are vital for antimicrobial stewardship, particularly as global antimicrobial resistance rises. The primary objectives of this study were to evaluate the tolerability of a < 0.75 x 109/l ANC cut-off for antimicrobial prophylaxis in dogs after receiving chemotherapy and its impact on antimicrobial prescription. Predicted nadir ANCs (pnANCs) were stratified into 6 groups (< 0.75 x 109/l [receiving antimicrobial prophylaxis], 0.75–0.99x109/l, 1–1.49x109/l, 1.5–1.99x109/l, 2.0–3.59x109/l and 3.6–12x109/l [reference interval]). The incidences of post-nadir febrile neutropenia (FN) and non-haematological toxicity (NHT) were compared between groups. Five hundred and eighty-six pnANCs were recorded for 181 dogs. There were 4 episodes of post-nadir FN and 90 episodes of post-nadir NHT. There was no significant difference in incidence of post-nadir FN (P = 0.063) or post-nadir NHT (P = 0.084) between pnANC groups. Antimicrobial prophylaxis was prescribed following 8.8% of the chemotherapy administrations; had cut-off values of < 1.0x109/l or < 1.5x109/l been used it would have been prescribed in 15.3% and 25.8% of cases respectively. An ANC cut-off of < 0.75x109/l for antimicrobial prophylaxis appears to be well tolerated and minimises the prescription of antimicrobials