Residue Depletion and Tissue-Plasma Correlation of Methyl-3-quinoxaline-2-carboxylic Acid after Dietary Administration of Olaquindox in Pigs

A residue depletion study was performed to investigate the tissue kinetics and tissue-plasma correlation of methyl-3-quinoxaline-2-carboxylic acid (MOCA), the marker residue of olaquindox (OLA), in pigs. Twenty-five pigs were randomly divided into a test and a control group. The former group was treated with 100 mg/kg OLA in its feed for 30 consecutive days, and the latter was given blank feed for the same period. One control and four treated animals were slaughtered at 0.5, 3, 10, 17, and 28 days post-medication. Muscle, liver, kidney, fat, and plasma samples were collected and analyzed using the validated high-performance liquid chromatography method (HPLC). Results showed that the tissue concentration of MQCA in the liver > kidney > fat > muscle, at almost all time points. The half-lives of MQCA in the muscle, liver, kidney, fat, and plasma were 12, 8, 15, 8, and 6 days, respectively. A withdrawal period of 38 days was calculated using the statistical method recommended by the European Medical Evaluation Agency (EMEA). Good correlations between tissue and plasma MQCA levels were found in the present study with correlation coefficients of more than 0.92. These correlations would be helpful in the routine monitoring of OLA in porcine tissues, without sacrificing the animals.