Antimicrobials premixes are the presentation of choice to administer drugs simultaneously to groups of animals in intensive husbandry systems that require treatment for pathologies of bacterial origin. Among the premixes available for use in poultry, florfenicol and oxytetracycline are commonly administered via food or water. However, their actual concentration in premixes must meet on-label statements to ensure plasma concentrations reach effective therapeutic levels. Hence, this work was designed for the purpose of verifying whether the concentration of antimicrobial present in five premixes matched their on-label statement. Three oxytetracycline premixes, and two of florfenicol, were analysed using a Xevo TQ-S micro UPLC-MS/MS, and an ABSciex API4000 HPLC-MS/MS, respectively. Analytical methodologies were implemented and validated, showing an R2 ≥ 0.99 for the calibration curves. Oxytetracycline was detected in these premixes at concentrations exceeding on-label statements by 13.28%, 21.54%, and 29.68%, whereas florfenicol concentrations detected in premixes were 13.06% and 14.75% lower than expected. Consequently, this work shows that the concentration of active ingredients that are present in commercial formulations effectively differ from those stated on premix labels, and it also highlights how unpredictable their range of variability might be. This must be addressed through solid and updated laws that guarantee an effective pharmaceutical product.
Keywords: HPLC-MS/MS; UPLC-MS/MS; antimicrobial premixes; florfenicol; oxytetracycline.