Significance and Impact of the Study: This study shows that chemotherapy drugs commonly used in veterinary oncology have an effect of the growth of canine isolates of Escherichia coli and Staphylococcus pseudintermedius. No associations between susceptibility to chemotherapeutic drugs and antibiotics were found, which does not support selection of antimicrobial resistance by chemotherapy drugs. AbstractThe ability of chemotherapeutic agents to affect the growth of common bacterial pathogens and the relationship between the effects of chemotherapeutics and antimicrobials is largely unknown. The purpose of this study was to describe the susceptibility of canine bacterial isolates to chemotherapeutic agents and to compare these results to their antimicrobial susceptibility. The effects of bleomycin, doxorubicin, cytarabine, cyclophosphamide, methotrexate, 5-fluorouracil and gemcitabine on the growth of 33 Staphylococcus pseudintermedius isolates and 32 Escherichia coli isolates from dogs was determined by agar dilution. In addition to MICs, the lowest drug concentration associated with a decreased colony size was recorded. Results were compared to the MICs of a panel of antimicrobial agents. Bleomycin consistently inhibited bacterial growth of S. pseudintermedius and E. coli. Doxorubicin inhibited S. pseudintermedius but not E. coli while the opposite was seen for gemcitabine. Reduction in colony size on exposure to 5fluorouracil for both organisms, and methotrexate for S. pseudintermedius was seen. No observable effect of cyclophosphamide or cytarabine was observed. Associations between elevated MICs to chemotherapeutic drugs and antimicrobial resistance were not found. These results indicate that chemotherapeutic agents affect the growth of bacteria, but do not support a role in the selection of antimicrobial resistance.Letters in Applied Microbiology ISSN 0266-8254

Adverse reaction to apomorphine in a Collie homozygous for the ABCB1-1 D ( MDR1 ) mutationA nine-month-old 30 kg spayed female rough collie and two other dogs, an eight-month 31·5 kg intact male Belgian shepherd and a 2·5-year 52 kg neutered male Bernese mountain dog, were presented shortly after ingestion of an unknown quantity of acetaminophen tablets by at least one of the dogs. Vomiting was induced by administering 2 mg apomorphine in the conjunctival sac of each dog. Emesis was more severe in the collie (number of events and duration), and she experienced greater central nervous system (CNS) depression compared to both other dogs despite conjunctival rinsing, but recovered completely from this episode. MDR1 genotyping identified the collie as MDR1 mutant/mutant (homozygous for the ABCB1-1 D gene mutation) while the other two dogs were MDR1 normal/normal.Although apomorphine has not been described as a P-glycoprotein substrate, other opioids, including loperamide and butorphanol, are known substrates for canine P-glycoprotein (Mealey & Fidel 2015 ). Dogs affected by the MDR1 mutation experience exaggerated CNS depression compared to MDR1 wildtype dogs when treated with these drugs because defective P-glycoprotein allows greater brain penetration. Similarly, the collie described here experienced exaggerated CNS depression compared to the other dogs suggesting greater CNS penetration of apomorphine. While this report suggests that apomorphine may be a substrate for P-glycoprotein, further investigation would be necessary to confirm this. However, it may be prudent to avoid apomorphine as an emetic in dogs with the MDR1 mutation.

Objectives To determine the effect of vincristine administration on the platelet count, platelet morphology and incidence of thrombocytopenia in dogs diagnosed with lymphoma. Material and Methods Medical records of 59 dogs with lymphoma receiving vincristine sulphate were reviewed retrospectively. Results Following vincristine administration the platelet count was higher and the number of thrombocytopenic patients was lower. No difference was found in the number of dogs with enlarged and elliptical platelets following vincristine treatment. Clinical Significance Vincristine administration increases platelet counts in dogs with lymphoma. It is not contra‐indicated to administer vincristine to dogs with lymphoma that are thrombocytopenic.

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