Withdrawal time of four pharmaceutical formulations of enrofloxacin in poultry according to different maximum residues limits

To ensure delivery of safe animal products to consumers, the withdrawal time (WDT) of drugs must be respected. Property differences among pharmaceutical formulations, for the same drugs, can lead to differences in the WDTs estimation. The WDTs of four commercial formulations of enrofloxacin (ENRO) in broiler chickens, considering MRLs established by different countries, were studied. Two hundred-thirty-four broiler chicks were allotted among four groups; the formulations were orally administered daily with 10 mg⁄ kg bw. After treatment, six chickens of each group and two controls were slaughtered daily until day 9 post-treatment. Samples of muscle and liver were collected, and analyzed using HPLC-MS-MS. The WDTs among formulations of ENRO showed differences of 24 and 48 h. Based on the European Community and Chile MRLs of 100 lg ⁄ kg (muscle) and 200 lg ⁄ kg (liver), the WDTs did not exceed 5 days. When Japan MRL was considered (10 lg ⁄ kg,), theWDTs increased up to 8 days. These results indicate that for WDTs determination, the differences among pharmaceutical formulations of a drug must be considered as well as the MRLs.The National Fund for Scientific and Technological Development (FONDECYT) offered financial support. Project No. 1070419