Physiologically Based Pharmacokinetics Model For Furazolidone In Pigs

Physiologically based pharmacokinetics (PBPK) models predict drug disposition based on mass balance. PBPK model is predictive and flexible in terms of dose, route of administration, and species. Current uses of PBPK models include human health risk assessment, design of rational dosing regimens, and mechanistic studies of drug interactions. In veterinary medicine, there are only a few validated models and more focus should be addressed in this area. Furazolidone has been prohibited for use in food animal production worldwide for its carcinogenicity and mutagenicity, but it is still illegally used in some farms due to its effectiveness and cheap price. Because of the food safety and economical concerns, it is necessary to find an efficient and low-cost way to monitor the misuse of furazolidone in food-producing animals. Therefore, a quatitaitve indirect competitive enzyme-linked immunosorbent assay was developed for 3-amino-2-oxazolidinone in animal tissues. Then a PBPK model on furazolidone in pigs was developed to predict the 3-amino-2-oxazolidinone residue in tissues of pigs. The developed PBPK model successfully predicted AOZ elimination in tissues of pigs. This use of a PBPK model in drug residue in food producing animal will be of great value for residue surveillance and research of food safety.1. Development of a quatitative analysis method for 3-amino-2-oxazolidinone in animal tissuesAn indirect competitive enzyme-linked immunosorbent assay was developed for quatitative analysis of 3-amino-2-oxazolidinone in animal tissues. The sample preparation was simple and effective included water bath treatments, acid hydrolysis combined with overnight derivatization of AOZ by benzaldehyde. A good linearity was achieved over a concentration range of 0.05 to 12.15μg/L, and the IC50 value was 0.96μg/L. The limit of detection and the limit of quantification were 0.15μg/kg and 0.3μg/kg respectively. The recoveries of AOZ in all tissues were between 60%-120% at the levels of 0.3,1.0, and 2.0 (5.0)μg/kg. The inter-assay variability was less than 20%. The modified ic-ELISA was applied in quantification of AOZ elimination in carp and was compared with LC-MS/MS and a commercial ELISA kit. Therefore, the present assay is considered a rapid, accurate, reliable, and inexpensive method for the detection of furazolidone-residues in tissues of food-producing animals. The development of the ELISA provides a reliable tool for developing the PBPK model of furazolidone in pigs.2. Development of a physiologically based pharmacokinetic model for furazolidone in pigsA flow-limited, physiologically based pharmacokinetic model for use in estimating concentrations of 3-amino-2-oxazolidinone after furazolidone administration to swine was developed. Liver was assumed to be the only metabolic site of furazolidone, and 3-amino-2-oxazolidinone was assumed to be formed directly from furazolidone. For the parent compound furazolidone, the model included compartments for blood, liver and an extra compartment representing the remaining carcass. Compartments for the metabolite AOZ included blood, muscle, liver, kidney adipose, and the remaining carcass. The model was created and optimized by use of computer software ACSLxtreme. To validate the model, a tissue depletion of AOZ was studied in pigs. The predicted curve simulated by the model typically under predicted concentrations at early time points but had excellent accuracy at later time points. Specific tissue correlations for plasma, muscle, kidney, and liver tissue compartments were above 0.97. Sensitivity analysis was completed to evaluate the importance of each constant on the whole model. Sensitivity analysis revealed that absorbtion rate, renal clearance, and tissue-plasma coefficient were the most important constants included in the model. This model enabled us to accurately predict AOZ depletion in swine tissues. It has great significance for food safety and prediction of drug residues in edible tissues. 3. Extrapolation of the furazolidone physiologically based pharmacokinetic modelThe extrapolations of the developed PBPK model were studied. The extrapolations included dose extrapolation, interspecies extrapolation, and drug extrapolation. In interspecies extrapolation, the parameters related to AOZ were fixed, the physiological parameters of fish were obtained from literature, and a slight modification was made to scale the residue depletion of AOZ from pigs to fish. The results showed that the predicted concentrations could represent the measured concentrations. In drug extrapolation, the target drug was choosen as AMOZ, metabolite of furaltadone. The physiological parameters of pigs and the structure of the AOZ PBPK model were fixed, some biochemical parameters of AMOZ were estimated to extrapolate the AMOZ PBPK model in pigs. The results showed good prediction ability of the extrapolation models.In conclusion, an accurate quantitative method was developed for determination of AOZ in food producing animal tissues. A PBPK model on furazolidone was developed in pigs. Sensitivity analysis and Monte Carlo analysis has been carried out to evaluate the sensitivity and uncertainty of parameters in PBPK model. The developed PBPK model has been extrapolated on interspecies and drug. The PBPK model of furazolidone residue in pigs provided a basis on PBPK model use in evaluating the drug residues in food producing animals, and will be of great value for residue surveillance to assure the food safety.