Rapid liquid chromatographic method for the control of doxycycline and tiamulin residues and their metabolites in vivo assays with pigs: Treatment and depletion

Results gained from in vivo metabolism could be more authentic to reflect the biotransformation of drugs than in vitro metabolism. This paper discusses the development and characterization of an analytical method for controlling tiamulin (TIA) and doxycycline (DOX) residues in pig plasma and urine, as well as their in vivo biotransformation during treatment and suppression steps at pig farms. For such a purpose, urine samples were taken daily (24-hr intervals) during treatment and until day 8 after last dose. Plasma samples were collected on the last treatment day and up to days 4 and 7 after the last dose. Only traces of TIA and their metabolites have been still detected 8 days after the last day of therapy, in agreement with the period of suppression of both antibiotics set by the manufacturers in 7 days. It was estimated that TIA and DOX half-lives were of two days and one day, respectively. TIA and DOX metabolites have been identified for the first time in plasma and urine pig samples during treatment and suppression steps.