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Gamithromycin is a new macrolide antibiotic that is only registered for use in cattle to treat respiratory disorders such as bovine respiratory disease. The aim of this study was to determine the pharmacokinetics of gamithromycin in broiler chickens. Gamithromycin (6 mg/kg of BW) was injected intravenously (IV) or subcutaneously (SC) to six 4-wk-old chickens in a parallel study design, and blood was collected at different time points postadministration. Quantification of gamithromycin in plasma was performed using an in-house validated liquid chromatography-tandem mass spectrometry method and the pharmacokinetics analyzed according to a 2-compartmental model. Following IV administration, the mean area under the plasma concentration-time curve (AUC0→∞), and α and β half-life of elimination (t1/2el α and t1/2el β) were 3,998 h•ng/mL, 0.90 h, and 14.12 h, respectively. Similar values were obtained after a SC bolus injection, i.e., 4,095 h•ng/mL, 0.34 h, and 11.63 h, for AUC0→∞, t1/2el α, and t1/2el β, respectively. The mean maximum plasma concentration (889.46 ng/mL) appeared at 0.13 h. Gamithromycin showed a large volume of distribution after IV as well as SC administration, 27.08 and 20.89 L/kg, respectively, and a total body clearance of 1.61 and 1.77 L/h•kg, respectively. The absolute bioavailability was 102.4%, showing that there is a complete absorption of gamithromycin after a SC bolus injection of 6 mg/kg of BW.

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