Study Of Metabolites Of Enrofloxacin In Scophthalmus Maximus, Carassius Auratus And Cyprinus Carpio

Enrofloxacin is a third-generation synthetic quinolone broad-spectrum antibiotic and has good killing and resisting effects on Gram-positive bacterium and Gram-negative bacterium. Being convenient to deliver, high and stable in blood concentration and free from cross resistance with common antibiotics, enrofloxacin is widely applied to livestock and poultry industry. The metabolites and metabolic pathways of enrofloxacin under the action of fungi or inside livestock and poultry have been reported. Ciprofloxacin is the major metabolite of enrofloxacin in livestock and poultry. About 20%~60% enrofloxacin is metabolized to ciprofloxacin. It is generally accepted that the major metabolite of enrofloxacin inside most aquatic animals is ciprofloxacin produced by removing ethyl from ethyl-piperazine. However, there were few reports on other metabolic pathways and other metabolites inside aquatic animals on the content, the distribution and the mass balance of enrofloxacin and its metabolites after metabolism inside aquatic animals, except Scylla serrate, carassius aauratus Gibelio and Litopenaeus vannamei.In the present study, Scophthalmus maximus, Carassius auratus and Cyprinus carpio were fed with enrofloxacin at a dose of 30 mg/kg?bw through oral perfusion under at the water temperatures of 21±1℃, 21±1℃ and 19±1 ℃ respectively; ultra-performance liquid chromatography / qudropole time-of-flight mass spectrometry(UPLC/Q-TOF MS) was utilized to detect enrofloxacin and its metabolites inside skin, muscle, liver, gill, kidney and plasma of the three fishes as well as aquatic water; the mass spectral characteristics of the metabolites showed that the metabolites and enrofloxacin were highly similar in chemical structures. 48 h after dosing, 97.26% ~ 99.06% of enrofloxacin existed originally inside the Scophthalmus maximus along with 0.48% ~ 1.78% ciprofloxacin; 97.78% ~ 99.18% of enrofloxacin existed originally inside the Carassius auratus along with 0.52%~1.39% ciprofloxacin; 94.44%~98.01% of enrofloxacin existed originally inside the Cyprinus carpio along with 0.58% ~ 3.13% ciprofloxacin. The six major metabolic pathways and metabolites of enrofloxacin inside the three fishes were similar and included ciprofloxacin produced by removing ethyl from the piperazine-N of enrofloxacin, decarboxylated metabolites produced through decarboxylation of enrofloxacin, ethylene-removed metabolites produced through breakage of the piperazine of enrofloxacin, dehydrated metabolites produced through dehydration of enrofloxacin, three hydroxylated metabolites produced through hydroxylation of enrofloxacin, and glucuronidated metabolites produced through glucuronidation of enrofloxacin, wherein the metabolites of enrofloxacin, which were produced through decarboxylation, ethylene removal and dehydration inside the fish bodies, had not been reported in aquatic animals. The metabolism extent of enrofloxacin in the fish body was far less than that of livestock and poultry. After entering the fish bodies, most of the enrofloxacin existed in an original form, quite a little part of the enrofloxacin was metabolized into the ciprofloxacin, and also, there were still some other metabolites.In Scophthalmus maximus, 4h after administration, enrofloxacin and ciprofloxacin concentration in liver and plasma got maxium levels respectively, 8h after administration enrofloxacin concentration in skin, muscle,gill and kidney got maxium levels respectively. The tissues which contained enrofloxacin from the highest level to the lowest level were plasma, kidney, liver, gill, skin and muscle. The enrofloxacin concentration in plasma and kidney were 41.63 μg/m L and 38.73 μg/g respectively. The tissues which contained ciprofloxacin from the highest level to the lowest level were plasma, liver, kidney, gill, skin and muscle. The ciprofloxacin concentration in plasma and kidney were 331.86 ng/m L and 170.04 ng/g. Kidney had the highest content of glucuronidated and ethylene-removed metabolites. In Carassius auratus, 4h and 8h after administration enrofloxacin and ciprofloxacin concentration got maxium levels respectively. The tissues which contained enrofloxacin from the highest level to the lowest level were plasma, kidney, liver, gill, muscle and skin. The enrofloxacin concentration in plasma and kidney were 44.34μg/m L and 28.53 μg/g respectively. The tissues which contained ciprofloxacin from the highest level to the lowest level were kidney, liver, plasma, gill, muscle and skin. The ciprofloxacin concentration in kidney and liver were 145.74 ng/g and 93.74 ng/g. The plasma had the highest content of glucuronidated metabolites, and the kidney had the highest content of ethylene-removed metabolites. In Cyprinus carpio, 24 h and 48 h after administration enrofloxacin and ciprofloxacin concentration got maxium levels respectively. The tissues which contained enrofloxacin from the highest level to the lowest level were plasma, kidney, liver, gill, muscle and skin. The enrofloxacin concentration in plasma and kidney were 33.05 μg/m L and 18.13 μg/g respectively. The tissues which contained ciprofloxacin from the highest level to the lowest level were kidney, liver, gill, plasma, muscle and skin. The ciprofloxacin concentration in kidney and liver were 286.65 ng/g and 200.11 ng/g. The plasma had the highest content of glucuronidated metabolites, and the kidney had the highest content of ethylene-removed metabolites. 48 h after administration, enrofloxacin and its metabolites were various in kinds and high in concentration and content inside the plasma, the liver, the kidney and the gill in three fishes, the plasma played a role of transportation, the liver and the kidney were the major organs for metabolizing enrofloxacin in fish.The thesis systematically analyzed and identified possible metabolites of enrofloxacin in Scophthalmus maximus, Carassius auratus and Cyprinus carpio, provided drug metabolic pathways, analyzed and compared the distribution and the content of enrofloxacin and its metabolites inside different tissues of the three fishes within different dosing time periods, and meanwhile further provided theoretical basis for establishing maximum residue limit of enrofloxacin in fish in China.