The entire Symposium on Antimicrobial Agents will be available for purchase as a bound booklet from the We use cookies to help provide and enhance our service and tailor content and ads. Six replicates of Quality Control (QC) samples containing tulathromycin at each of the three concentrations 1.5, 15, and 80 (ng/mL) were prepared similarly by adding 7.5 and 75 of the 100 ng/mL and 4 μL of the 10 µg/mL working standards to 0.5 mL drug‐free bison serum samples. Working standards were made new each day.In anticipation that serum concentrations of tulathromycin in incurred samples might exceed the upper limit of our calibration standards, a ‘dilution integrity’ experiment was conducted by extracting samples intentionally fortified with tulathromycin at concentrations greater than the upper limit of the calibration curve in duplicate and diluting them 2‐fold, 5‐fold, and 10‐fold so that their concentrations fell within the calibration range. The method was successfully applied to provide the first ever reported PK data for the absorption and depletion of tulathromycin residues in bison and deer sera as well as conduct a depletion study of tulathromycin in muscle and lung tissues in white‐tailed deer.One of the co‐authors (KB) gratefully acknowledges funding from the Saskatchewan Agri‐Food Innovation Fund. Glass wool was added to each cartridge and the sample was loaded. The validated method was linear from 0.8 ng/mL to 100 ng/mL for bison serum, 0.6–50 ng/mL for deer serum, 100–2500 ng/g for deer muscle tissue and 500–5000 ng/g for deer lung tissue. Three 2.00 ± 0.05 g of each tissue sample (lung or muscle) were weighed into individual 50 mL centrifuge tubes. The LOD and LOQ for tulathromycin A in bison serum were 0.3 ng/mL and 0.8 ng/mL, respectively, 0.2 and 0.6 ng/mL for deer serum and 0.6 ng/g for lung and muscle tissue, respectively. Sample dilution (0.5 mL + 4.5 mL buffer) also failed to improve the extraction procedure. By continuing you agree to the Copyright © 2020 Elsevier B.V. or its licensors or contributors. A new method was therefore developed for bison serum which used a simple acetonitrile and phosphate buffer combination to extract tulathromycin from 0.5 mL of serum. All test samples, calibration, and QC standards prepared on the day of analysis were treated as follows to extract tulathromycin.To each sample was added 5.0 mL acetonitrile and 5.0 mL of 50 mM KCartridges (Bond Elut–CBA, 200 mg, 3 mL, Agilent Technologies, Ottawa, ON, Canada) were each conditioned with 3.0 mL acetonitrile and 3.0 mL of phosphate buffer. Liquid chromatography coupled to mass spectrometry (LC‐MS) has become standard practice in pharmacokinetic analysis for the analysis of drugs in food and biological samples due to its excellent sensitively and selectivity and the ability to quantify drugs at trace levels.Tulathromycin analytical standard (>95%) was a kind gift from Pfizer Inc. (Groton, CT, USA). >100 ng/mL for bison serum).Because there were no available certified reference materials (CRMs), once the validation process was completed using fortified material, an additional set of ‘blind analysis’ was conducted over a two‐day period during which samples were prepared by one analyst, randomized, and presented ‘blind’ to an experienced analyst for analysis using the described method. Chromatography was performed by gradient elution using a Poroshell 120 EC‐C18 column (2.1 x 50 mm, 2.7 µm, Agilent Technologies, Ottawa, ON, Canada) with a 0.5 µm frit (Canadian Life Science, Edmonton, AB, Canada) attached to each end. These drug‐free muscle and lung tissue samples were used for developing and validating the method in the white‐tailed deer. Published by Elsevier Inc. All rights reserved.ScienceDirect ® is a registered trademark of Elsevier B.V.