Residues of aminoglycoside antibiotics in eggs after medication of laying hens

Oral bioavailability and egg drug residue of lincomycin in laying hens after different treatment

Lincomycin (LCM) is an antibiotic used to treat severe bacterial infections in livestock and companion animals. In this study, we aimed to investigate the oral bioavailability of LCM with PK data after IV and PO administration and to compare differences in drug residue patterns in eggs. To ensure food safety, an additional study on egg residue was conducted using 3 different commercial LCM drugs. For bioavailability study, laying hens were divided into oral and intravenous (n = 8/group) groups and received single dose (10 mg/kg) of LCM. The limits of quantification for LCM were 0.729 μg/mL and 0.009 mg/kg in plasma and eggs, respectively. The oral group exhibited a significantly lower average serum drug concentration than the IV group, with a bioavailability of 2.6%. Furthermore, the egg residue profiles confirmed reduced systemic drug exposure after oral administration. For the commercial LCM drug egg residue experiment, laying hens were divided into low- and high-dose groups (n = 12/group) for each drug and treated with the recommended dosage and administration method for each respective drug. The eggs were collected and analyzed until 14 d after the last drug treatment. Despite differences in the LCM content and formulation among commercial drugs, all the tested commercial drugs showed average concentrations below the MRL in eggs within approximately 3 d after the last drug treatment. In this study, we have confirmed that LCM has a low oral absorption rate in laying hens, and this was consistent with the findings from the egg residue profiles. Further studies are requested to elucidate the exact reasons for evidently low oral drug absorption in laying hens.

Antimicrobial agents in laying hens

The European Union permitted 6 antimicrobial agents that can be used in laying hens. These are colistin, tyrosine, neomycin, oxytetracycline, chlortetracycline, and erythromycin. Antimicrobial drugs are used today primarily for the prevention and treatment of diseases in poultry and often (not in the EU) to stimulate growth. Because these drugs are often used irrationally, there are good chances that their residues will be found not only in poultry meat but also in the eggs within a certain period after the termination of treatment. In addition to the administration of authorised VMPs, the residues in eggs can be the result of erroneously applied medicated food, the contamination of the food with some antimicrobial drug in the mixing unit, as well as ?extra-label? use of drugs in poultry. The antimicrobial agents are distributed in the body and deposited in the eggs, mainly in the yolk where they persist longer than in the albumen. Drugs that are poorly absorbed from the gastrointestinal tract (aminoglycosides, aminocyclitols, polymyxins) cannot be detected in the eggs, while the residues of some antimicrobial drugs can be detected for up to two months (chloramphenicol) after the last treatment. The rational use of drugs in veterinary medicine has manifold significance. When using drugs only when they are really necessary (indicated), in the right dose and route of administration, the potential damage can be reduced and efficiency increased, while the risk of microorganism resistance development would be significantly decreased. All of this becomes more important when these drugs are used in food animals.

Pharmacokinetics of veterinary drugs in laying hens and residues in eggs: a review of the literature

Poultry treated with pharmaceutical products can produce eggs contaminated with drug residues. Such residues could pose a risk to consumer health. The following is a review of the information available in the literature regarding drug pharmacokinetics in laying hens, and the deposition of drugs into eggs of poultry species, primarily chickens. The available data suggest that, when administered to laying hens, a wide variety of drugs leave detectable residues in eggs laid days to weeks after the cessation of treatment.

Residues of gentamicin in eggs following medication of laying hens

1. Gentamicin was injected subcutaneously and intramuscularly into 5 groups of 10 laying hens and its concentration was determined in albumen, yolk and whole egg. 2. Groups 1 and 3 were intramuscularly injected with doses of 10 and 25 mg/kg while groups 2, 4 and 5 were subcutaneously injected with doses of 10, 25 and 50 mg/kg, respectively. 3. The final gentamicin concentration in albumen was measured on d 3 for groups 1 and 2; on d 4 for groups 3 and 4, and on d 5 for group 5. Concentrations in yolk and whole egg were measured on d 7, 10 and 12. 4. Gentamicin recovery was as follows: 2% in groups 1 and 2, 2.5% in groups 3 and 4, and 3% in group 5. 5. Most of the residue (approximately 90%) was recovered from the yolk.

Transference of dietary veterinary drugs into eggs

Twelve veterinary drugs, bacitracin (BC), chloramphenicol (CAP), chlortetracycline (CTC), oxytetracycline (OTC), tylosin (TS), amprolium (APL), furazolidone (FZD), nicarbazine (NCZ), ormetoprium (OMP), sulfadimidine (SDD), sulfadimethoxine (SDM) and sulfamonomethoxine (SMM) were fed to laying hens for 14 days, each at a dietary concentration of 500 mg/kg. The concentrations of the drugs in the eggs from these birds were determined at 2-day intervals for 14 days after the start of feeding. The relationship between the concentrations of the drugs (mg/kg) in the eggs and the number of days after the start of feeding was analysed by regression and covariance analyses. The concentrations of the drugs in the eggs became constant after 4 days for OTC, TS, FZD and all the sulfonamides, and after 6 days for CAP, APL, NCZ and OMP. No BC or CTC was detected in the eggs. The transfer rates of the 10 drugs (excluding BC and CTC) from the feed to eggs varied from 0.005% for TS up to 1.540% for SDD.

Decreasing profile of residual sulphaquinoxaline in eggs

1. Sulphaquinoxaline (SQ) was added to the diet of laying hens at 200 mg/kg for 7 successive days. Contents (mg/kg) of SQ in albumen and egg yolk of eggs laid after drug withdrawal were determined by high pressure liquid chromatography (HPLC). The contents in the whole egg were calculated taking into consideration the respective weights of albumen and egg yolk. 2. A time-lag in the initiation of decrease of SQ from eggs after the withdrawal of dietary SQ was observed. 3. The decreasing pattern from whole egg could be well described by the following equation with a time-lag of 1.0 d, y = 2.07 e-0.5620(t-1.0), where y is the SQ content in whole egg, t is time (d) after the withdrawal of dietary SQ and a constant of 2.07 is the SQ content in whole egg laid at the withdrawal. 4. Biological half-life of SQ in the whole egg was estimated to be 1.23 d. 5. From the above equation, SQ residue of whole egg laid at 9th d after withdrawal will be below the detection limit of 0.01 mg/kg.

Analytical strategies for the screening of veterinary drugs and their residues in edible products

The development of analytical strategies for the regulatory control of drug residues in food-producing animals is discussed. Analytical methods for the determination of veterinary drugs in edible products are based on microbiological, immunochemical and physicochemical principles. Because of complexity of biological matrices such as egg, milk and meat, well designed, and often sophisticated, off-line or on-line sample treatment procedures are essential, especially when utilising physicochemical multi-residue screening procedures. Since large series of samples have often to be analysed, automation is increasingly becoming important. Confirmation of the identity of drug residues and validation of the analytical results implies the use of adequate analytical methods. In its turn, this requires well established criteria for those methods and/or equivalent reference methods.

Residues of macrolide antibiotics in eggs following medication of laying hens

1. The elimination kinetics of four macrolide antibiotics (tylosin, erythromycin, spiramycin and josamycin) in eggs were determined separately for albumen and yolk after oral administration through either drinking water or diet or after intramuscular injection. 2. Residues were assayed by a plate diffusion technique in cylinders with Micrococcus luteus as the test-organism. 3. Drug excretion was usually over a longer time in the yolk. Spiramycin was the most highly excreted in the egg whereas seven to eight times less tylosin and erythromycin was transferred. The conditions for the use of macrolide antibiotics in laying hens are discussed.