Fosfomycin residues and withdrawal time in eggs after oral administration to laying hens

DIÉGUEZ, SUSANA; SORACI, ALEJANDRO LUIS; CRISTÓFARO, AGUSTÍN; MARTÍNEZ, GUADALUPE; FERNÁNDEZ PAGGI, MARÍA BELÉN; TAPIA, MARÍA OFELIA; HARKES, ROBERTO

Nantes

Congreso; AEVPT 13th International Congress of the European Association for Veterinary Pharmacology and Toxicology; 2015

European Association for Veterinary Pharmacology and Toxicology

Fosfomycin is a bactericidal broad spectrum antibiotic widely used in poultry production in South and Central America and Asia. Data on fosfomycin residues accumulation in eggs is not available so far and withdrawal times stated in labels of commercial products greatly differ from each other and lack of scientific support.The goal of the present study was to determine fosfomycin withdrawal time from egg white and yolk after administration of different formulations (in drinking water and feed) to laying hens.Two homogeneous groups of 20 Lohmann laying hens each, were treated with 160 mg/Kg/day of a commercial formulation containing 25% calcium fosfomycin (Fosbac , Bedson SA, Argentina), administered for seven days in drinking water or premix accordingly. Besides a control group of untreated animals was also considered. Fosfomycin administration took place 1 hour after egg laying in order to synchronize it with ovulation (which occurs 30 min after egg laying), since the dynamic process of yolk formation significantly influences incorporation and storage of drug residues. After the end of the treatments, eggs were collected daily and fosfomycin concentrations were quantified by HPLC-MS/MS. Analytical method development and validation was carried out following international guidelines. For withdrawal time calculation EMEA WT 1.4 software was used, and an MRL of 0.5 µg/g was considered (established by Japan for animal tissues other than eggs, but it is the only MRL value given by an official agency so far). Calculated withdrawal times were 0.46 and 4.02 days for white and yolk respectively when the antibiotic was administered in drinking water, and 1.37 and 4.6 days for white and yolk respectively when the antibiotic was administered in premix.Differences found in yolk and white may be due to the longer period of yolk formation which undergo a later stage of rapid growth, approximately two weeks before ovulation. Probably residues were incorporated and stored along dosing period in preovulatory yolks. Conversely, egg white is built in the latter period of whole egg development, just before eggshell formation, decreasing contact time with the antibiotic.