Effect Of Streptococcus Infection On Oxytetracycline Pharmacokinetics In Tilapia     Chun-Yao Chen, Gregory A. Wooster and Paul R. Bowser     Aquatic Animal Health Program, Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853     Bacterial infection can lead to dramatic physiological changes in affected fish. These changes have been reported to affect kinetics of drugs in both humans and animals, including drug metabolism, absorption and depletion. Currently, most pharmacokinetic studies are conducted on healthy fish, and from these studies withdrawal times were determined. Here we present a comparative pharmacokinetics study, using both healthy and infected fish. Tilapia (Oreochromisniloticus) and Streptococcus iniae were chosen to access the impact of infection on oxytetracycline pharmacokinetics, after dosing the fish intra-vascularly at 10 mg/kg body weight. Compared to healthy fish, those that were infected had much lower initial plasma concentrations and higher concentrations of OTC in the internal organs.  OTC concentrations in liver and trunk kidney remained higher in infected fish. Muscle concentrations peaked at a later time in infected fish and at higher concentrations than were observed in healthy fish.  However, whether the depletion time will be affected significantly in standard feed medication protocols remains to be investigated.    Preliminary experiments have been conducted to elucidate the mechanisms involved.  Blood chemistry data suggest that acute phase response might be induced in S. iniae infected tilapia. Similar changes in OTC pharmacokinetics can be induced by intraperitoneal injection of formalin-killed S. iniae cells one day before OTC administration.  However the degree of change in pharmacokinetics was smaller than that observed in S. iniae infected fish.  This indicates that the change in pharmacokinetics might be induced in part by a cellular component.