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Objective--To determine the pharmacokinetic properties of 1 IM injection of ceftiofur crystalline-free acid (CCFA) in American black ducks (Anas rubripes). Animals--20 adult American black ducks (6 in a preliminary experiment and 14 in a primary experiment). Procedures--Dose and route of administration of CCFA for the primary experiment were determined in a preliminary experiment. In the primary experiment, CCFA (10 mg/kg, IM) was administered to ducks. Ducks were allocated into 2 groups, and blood samples were obtained 0.25, 0.5, 1, 2, 4, 8, 12, 48, 96, 144, 192, and 240 hours or 0.25, 0.5, 1, 2, 4, 8, 24, 72, 120, 168, and 216 hours after administration of CCFA. Plasma concentrations of ceftiofur free acid equivalents (CFAEs) were determined by use of high-performance liquid chromatography. Data were evaluated by use of a naive pooled-data approach. Results--The area under the plasma concentration versus time curve from 0 hours to infinity was 783 h•µg/mL, maximum plasma concentration observed was 13.1 µg/mL, time to maximum plasma concentration observed was 24 hours, terminal phase half-life was 32.0 hours, time that concentrations of CFAEs were higher than the minimum inhibitory concentration (1.0 µg/mL) for many pathogens of birds was 123 hours, and time that concentrations of CFAEs were higher than the target plasma concentration (4.0 µg/mL) was 73.3 hours. Conclusions and Clinical Relevance--On the basis of the time that CFAE concentrations were higher than the target plasma concentration, a dosing interval of 3 days can be recommended for future multidose CCFA studies. [ABSTRACT FROM AUTHOR]