Which combination best describes substances that can cause chemical neutropenia in dogs?

• A. Chloramphenicol
• B. All of the above
• C. Estrogen
• D. Phenylbutazone

Answer: (D)

Chemical neutropenia happens when a drug suppresses the bone marrow’s production of neutrophils, lowering the number of these white cells in circulation and raising the risk of infection. Among the options, phenylbutazone is the substance most consistently associated with drug-induced bone marrow suppression in dogs, leading to neutropenia especially with prolonged use or higher doses. This makes it the best fit for causing this condition in dogs.

Chloramphenicol is infamous for hematologic toxicity, particularly bone marrow suppression, but in veterinary medicine its risk is more noted in cats and humans; in dogs it’s not as reliably linked to neutropenia. Estrogenic compounds can affect bone marrow in some species, but they are not as commonly implicated for canine neutropenia as phenylbutazone. Therefore, phenylbutazone stands out as the drug most classically connected to this finding in dogs. If drug-induced neutropenia is suspected, stopping the drug and monitoring the CBC are key steps.