Tissue distribution and residue depletion of oxytetracycline in the rabbit
Oxytetracycline (OTC) is an antimicrobial drug widely used in the rabbit for treatment of intestinal and respiratory diseases sustained by Pasteurella spp, Sa/mone//a spp. or E. Coli. This study was carried out to evaluate the distribution and residue depletion of oxytetracycline. The tissue distribution study was performed treating animals with a single dose of 80 mg of OTC per kg body weight (b.w.) in 2.7 kg rabbits. The residue studies were performed administering OTC vía drinking water (680 ppm) or vía pelleted food (1000 ppm). Real daily intake ranged from 50 to 80 mg per kg b.w. for 5 consecutive days. The drug tissue concentrations were determined by an HPLC method, with a quantification limit (LOQ) of 50 mg.kg·1 and a detection limit of 5-6 mg.kg·1according to considered tissue. The results of the study show that, in rabbits, OTC does not reach very high lissue concenlralions following oral administration vía medicated water or feed. Tissue residues fall below MRLs 72 and 48 hours following the withdrawal of medicaled water and feed respectively. Tissue concentrations of OTC following administration vía medicated water were greater than those recorded following administration via pellets: e.g, 200 to 700 vs <50mg.kg-1 in muscle or 200 to 600 vs 80 to 280 mg.kg-1 in liver. One hour after the single dose administration, the concentration was 350-850 mg.kg-1 in lung and twice of these values in kidneys.
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