OBJECTIVE: To calculate prescribed daily doses (PDDs) for selected antimicrobials and evaluate application of defined daily doses (DDDs) using an antimicrobial purchasing dataset. ANIMALS: Data from dogs and cats treated for bacterial cystitis at a veterinary practice network were evaluated. PROCEDURE: A dataset containing antimicrobial prescriptions for dogs and cats diagnosed with bacterial cystitis was evaluated. Median dose and frequency and median weight of treated animals were used to calculate PDDs. To account for differences in use between dogs and cats, an adjusted DDD was calculated based on adjustment for proportional use in dogs versus cats. RESULTS: PDDs for dogs and cats were determined and adjusted DDDs were calculated and applied to an antimicrobial purchasing dataset from 886 veterinary clinics, demonstrating the difference between mass-based and DDD data. CONCLUSIONS: DDDs can be estimated using prescription datasets, accounting for differences in weights (between and within species) and relative use between dogs and cats. These can be applied to broader (sales, purchase) datasets to provide a more detailed understanding of how antimicrobials are used. CLINICAL RELEVANCE: DDDs could be a useful measure for assessing mass-based antimicrobial use datasets as part of antimicrobial stewardship surveillance efforts.