Preliminary Study On Physiologically Based Pharmacokinetic Model Of Sulfamethoxazole In Tilapia

Sulfamethoxazole?SMZ?is a broad-spectrum antibacterial drug widely used in clinical medicine,animal husbandry and aquaculture.If the drug is improperly used in the breeding process,it will not only lead to the emergence of resistance to pathogens,but also make it possible to cause excessive drug residue in the fish body,thus endangering the health of the human body.Therefore,scientific and effective supervision of drug residues in aquatic products is very important,which depends on the study of drug residue patterns and prediction techniques.Therefore,preliminary predictions of drug residues appear to be crucial before aquatic products are marketed.At present,there are few studies on the residual rule of sulfamethoxazole in Tilapia,and there is no report on the construction of residue prediction model of sulfamethoxazole in animals.In this dissertation,the residue rule of sulfamethoxazole in Tilapia was systematically studied,and the determination method of plasma protein binding rate of sulfamethoxazole in Tilapia was explored,and the plasma protein binding rate and organ volume of Tilapia were studied.The measurement was finally merged with the residual data to construct a SMZ residual prediction model that was consistent with the actual production.The application of the prediction results can provide a supervision and technical support for protecting the consumption safety of products and avoiding unnecessary losses caused by SMZ residues.1.Determination of plasma protein binding rate of Sulfamethoxazole?SMZ?in Tilapia and comparison study.The effect of equilibrium time,different temperature?4,25,37°C?,different pH?7.4,7.8,8.2?,and drug concentration on the binding rate was investigated with an external equilibrium dialysis method to determine the best assay conditions for the determination of protein binding rate of SMZ in vitro by equilibration dialysis.Then,a comparative study of in vitro balanced dialysis and in vivo ultrafiltration was performed.The results showed that the protein binding rate of SMZ was not temperature-dependent but pH-dependent and drug-concentration-dependent.Finally,the equilibrium dialysis conditions were determined:dialysis in a dialysate at 4?and pH 7.4 for 48 h.Because pH of plasma rose from 7.4 before thawing to 8.2 after thawing,the best measurement conditions for in vitro ultrafiltration were deduced:4?,pH 7.4,that is,ultrafiltration was performed with fresh plasma at4?;Under the optimal conditions,the results of in vitro plasma protein binding assays were as follows:in the range of 0.5 to 10.0?g SMZ/mL dialysate,the in vitro SMZ plasma protein binding rate was 15.48%to25.12%,In the range of 10.0 to 60.0?g SMZ/mL dialysate,the in vitro plasma protein binding rate was maintained in the range of 14.65%to15.48%.The results of in vivo plasma protein binding assays were as follows:in the range of 1 to 5?g SMZ/mL plasma,the in vivo SMZ plasma protein binding rate was 15.34%to 20.1%,in the range of 10 to 20?g SMZ/mL plasma,the in vivo binding rate tended to be stable and maintained within the range of 12.7%to 14.9%,consistent with in vitro measurements.Finally,through comparative study of the two methods,the authors recommend the use of in vivo ultrafiltration method for the determination of plasma protein binding rate of sulfamethoxazole in Tilapia.This method is simple,short cycle,and good reproducibility.2.Residue elimination rule of sulfamethoxazole?SMZ?in Tilapia.Tilapia was continuously fed with 100 mg SMZ/kg body weight for 7 days.The results showed that after 8 h from the end of administration,the SMZ concentration in each tissue reached the highest point,and the order of size was:liver>skin>plasma>kidney>residue>gill>muscle.Three days after the completion of administration,SMZ was eliminated in each tissue and then dropped to a maximum residue limit?MRLs?of 0.1?g/g or less.The order was:muscle,kidney?gill,residue?,plasma,liver,and skin.After 16days from the end of administration,SMZ in muscle and kidney firstly decreased to 0.01?g/g or less,while SMZ in liver and skin remained and was higher than 0.01?g/g after 30 days after 16 days from the end of administration,mainly due to the reversible action of SMZ acetylation in the liver and the long-term accumulation of SMZ in the skin.The origin 8.5software was used to fit the residual data after 1 day of multi-dose oral administration to obtain the elimination curve equation.Thus,it can be seen that sulfamethoxazole is eliminated from the body in accordance with the first-order kinetic process,that is,it is obeyed the exponential distribution at the later stage of elimination:C_t=C₀ e^-?t,where C₀ and?are constants.By calculation,the elimination half-life of SMZ in plasma,muscle,liver,kidney,skin,gill,and residue tissues was 29 h,22 h,11 h,22h,35 h,26 h,and 32 h,respectively.According to the elimination curve equation,based on that maximum residue limit of SMZ in muscle is not higher than 0.1?g/g,the time required for muscles,blood,liver,kidneys,skin,gill,and residue tissues to fall to a safe level was calculated:88 h,154h,85 h,109 h,207 h,109 h and 121 h,respectively.Therefore,after administration,if the concentration of the drug in the muscle is to be monitored,the recommended withdrawal period is 4 days.If the drug concentration in the skin is to be monitored,the recommended withdrawal period is 9 days.3.In order to construct a physiologically based pharmacokinetic model of sulfamethoxazole in Tilapia,physiological and anatomical parameters,drug-specific parameters and elimination data of residual of various tissue modules in vivo were provided.The cooperatively constructed model had been increased from the first four basic modules?blood,muscle,skin,liver?to seven modules?plasma,muscle,skin,liver,kidney,gill,and residual tissue?.According to the requirements of model building,the study provided physiological and anatomical parameters,drug-specific parameters,and elimination data of residue for each tissue module in vivo.Through the calculation and optimization of model parameters,the accuracy of the model is improved.The results of sensitivity analysis showed that the renal clearance parameter has the greatest influence on the sensitivity of the model,and has a negative correlation with the model prediction result.Comparing the model predicted value with the actual measured value,the two were basically the same,the SMZ model predictive value in each tissue is generally slightly lower than the actual value in the early eradication period,and the elimination of the latter is just the opposite.It can be seen that using this model to predict and determine whether the product meets the national food safety standards,has credibility and security.