Hematologic follow-up of metamizole-associated Heinz body anemia in dogs.

Introduction: Heinz body (HB) anemia is uncommon in dogs. Metamizole is described as a potential trigger in isolated cases. Aim of the study: The present study describes the course of metamizole-associated HB anemia in dogs with the development of hematocrit, HBs, and eccentrocytes. In addition, the correlation between HBs, eccentrocytes, hematocrit, and reticulocytes is investigated. Materials and methods: In this prospective observational study, 25 dogs with metamizole-associated HB anemia were included. Hematologic examinations and blood smear evaluations for quantification of HBs and eccentrocytes (stained with brilliant cresyl blue and modified Wright's stain) were performed on day 0 and at the control intervals 1-3, 4-6, 7-13, and 14-20 days after discontinuation of metamizole and initiation of antioxidant treatment. Known alternative causes of oxidative erythrocyte damage were excluded. Data were analyzed using Kruskal-Wallis test, Friedman test, and Spearman correlation. Results: HB anemia was detected a median of 10 days after initiation of metamizole (median cumulative dose 720 mg/kg). On day 0, HB percentage did not correlate with metamizole dose or hematocrit. The eccentrocyte count did not correlate with metamizole dose, hematocrit, or reticulocyte count. However, a moderate to strong correlation was identified between HB percentage and reticulocyte count ( Conclusion: In dogs with concurrent disease, metamizole administration may be associated with clinically relevant erythrocyte oxidative damage. Discontinuation of metamizole and initiation of antioxidant therapy were followed by a decrease in HBs and recovery of hematocrit. The use of metamizole in multimorbid dogs should be carefully considered and accompanied by regular hematology controls.