Pharmacokinetics and tissue depletion of florfenicol in Leghorn and Taiwan Native chickens.

Florfenicol (Ff) is a synthetic antibiotic with a broad antibacterial spectrum and high therapeutic effectiveness that was specifically developed for veterinary use. In the present study, tissue residual levels and the pharmacokinetics of Ff after oral administration of 30 mg/kg to Leghorn and Taiwan Native chicken were studied. Furthermore, differential pharmacokinetics between leg and breast muscles were compared using samples collected from an optimized microdialysis model designed for avian species. Significant differences in C(max) were detected between the plasma and muscle microdialysates, and between the breast and leg microdialysates of the Leghorn chickens by noncompartmental pharmacokinetic analysis. After a single oral dose of Ff at 30 mg/kg, the drug was quickly absorbed and widely distributed with tissue penetration factors significantly different between leg and breast muscles. The serum protein binding of Ff was estimated to be 16.8 ± 1.2%. Significant breed differences in tissue depletion were noted and characterized by higher Ff concentration in the brain, lung, kidney and at least 12 h longer resident times in kidney, heart and spleen for Taiwan Native chicken. Results from this investigation demonstrate the practicality of using in vivo microdialysis in chickens for pharmacokinetic studies and reveal significant time-dependent differences in the free concentrations of Ff in leg and breast muscles. The tissue depletion study signified breed differences in tissue residue concentration and detection times between Leghorn and Taiwan Native chickens. Therefore, currently used withdrawal times for Ff in chickens can not be assumed safe for Taiwan Native chickens.

Development of amoxicillin enzyme-linked immunosorbent assay and measurements of tissue amoxicillin concentrations in a pigeon microdialysis model.

A sensitive ELISA was developed for the detection of amoxicillin (AMX) in serum, urine, and milk. The ELISA used an indirect competitive method produced by coating the plate with ovalbumin conjugated with AMX hapten. Antibodies against AMX-BSA were detected by a goat-antirabbit antibody conjugated with peroxidase. Calibration standard curves ranged from 1.28 ng/mL to 20 microg/mL [IC(50) (inhibition concentration 50%) = 100 ng/mL], and the limits of detection were 1.3, 2.7, and 4.8 ng/mL for urine, milk, and serum, respectively. The intra- and interassay variations were less than 4 and 9.6%. The antibody produced against AMX cross-reacted highly with penicillin G (77%); cross-reacted moderately with ampicillin, oxacillin, and cloxacillin (56.9, 51.4, and 48.8%, respectively); but was considered non-cross-reactive with dicloxacillin (7.4%), cefadroxil (<1%), and cefazolin (<1%). Concentrations of AMX were measured simultaneously in venous blood and muscles by using the developed AMX ELISA in an in vivo microdialysis model designed for pigeons. Following i.m. injection (25 mg/kg), AMX attained a peak blood level of 4.74 +/-0.30 mu g/mL and decreased with a half-life of 2.38 +/-0.16 h. In contrast, measurements in pectoral and femoral muscles exhibited delayed appearances, reduced peak concentrations, and prolonged half-lives of 4.07 +/-0.48 (pectoral) and 3.01 +/-0.26 (femoral) that were significantly different from each other and those in the blood (P < 0.05). Blood protein binding was calculated to be 27.9 +/-5.7%. This study demonstrated the semiquantitative application of a selective AMX ELISA in the first microdialysis procedure for continuous monitoring of drug levels in specific tissues of pigeons and maybe useful for related studies in other poultry species.