Pharmacokinetic/pharmacodynamic modeling of ketoprofen and flunixin at piglet castration and tail-docking.

This study performed population-pharmacokinetic/pharmacodynamic (pop-PK/PD) modeling of ketoprofen and flunixin in piglets undergoing routine castration and tail-docking, utilizing previously published data. Six-day-old male piglets (8/group) received either ketoprofen (3.0 mg/kg) or flunixin (2.2 mg/kg) intramuscularly. Two hours post-dose, piglets were castrated and tail docked. Inhibitory indirect response models were developed utilizing plasma cortisol or interstitial fluid prostaglandin E2 (PGE2) concentration data. Plasma IC50 for ketoprofen utilizing PGE2 as a biomarker was 1.2 µg/ml, and ED50 for was 5.83 mg/kg. The ED50 calculated using cortisol was 4.36 mg/kg; however, the IC50 was high, at 2.56 µg/ml. A large degree of inter-individual variability (124.08%) was also associated with the cortisol IC50 following ketoprofen administration. IC50 for flunixin utilizing cortisol as a biomarker was 0.06 µg/ml, and ED50 was 0.51 mg/kg. The results show that the currently marketed doses of ketoprofen (3.0 mg/kg) and flunixin (2.2 mg/kg) correspond to drug responses of 33.97% (ketoprofen-PGE2), 40.75% (ketoprofen-cortisol), and 81.05% (flunixin-cortisol) of the maximal possible responses. Given this information, flunixin may be the best NSAID to use in mitigating castration and tail-docking pain at the current label dose.

Dalbavancin Population Pharmacokinetic Modeling and Target Attainment Analysis.

Dalbavancin is indicated for the treatment of acute bacterial skin and skin structure infections caused by susceptible gram-positive microorganisms. This analysis represents the update of the population pharmacokinetics (popPK) modeling and target attainment simulations performed with data from the single-dose safety and efficacy study and an unrelated but substantial revision of the preclinical pharmacokinetic/pharmacodynamic target (fAUC/MIC, free area under concentration-time curve/minimum inhibitory concentration ratio). A 3-compartment distribution model with first-order elimination provided an appropriate fit, with typical dalbavancin clearance of 0.05 L/h and total volume of distribution of ∼15 L. Impact of intrinsic factors was modest, although statistically significant (P < .05) relationships with total clearance were found for the following covariates: creatinine clearance, weight, and albumin - dose adjustment was only indicated for severe renal impairment. Under the new nonclinical target, simulations of the popPK model projected that >99% of subjects would achieve the nonclinical target at MIC values up to and including 2 mg/L.

Integration of Food Animal Residue Avoidance Databank (FARAD) empirical methods for drug withdrawal interval determination with a mechanistic population-based interactive physiologically based pharmacokinetic (iPBPK) modeling platform: example for flunixin meglumine administration.

Violative chemical residues in animal-derived food products affect food safety globally and have impact on the trade of international agricultural products. The Food Animal Residue Avoidance Databank program has been developing scientific tools to provide appropriate withdrawal interval (WDI) estimations after extralabel drug use in food animals for the past three decades. One of the tools is physiologically based pharmacokinetic (PBPK) modeling, which is a mechanistic-based approach that can be used to predict tissue residues and WDIs. However, PBPK models are complicated and difficult to use by non-modelers. Therefore, a user-friendly PBPK modeling framework is needed to move this field forward. Flunixin was one of the top five violative drug residues identified in the United States from 2010 to 2016. The objective of this study was to establish a web-based user-friendly framework for the development of new PBPK models for drugs administered to food animals. Specifically, a new PBPK model for both cattle and swine after administration of flunixin meglumine was developed. Population analysis using Monte Carlo simulations was incorporated into the model to predict WDIs following extralabel administration of flunixin meglumine. The population PBPK model was converted to a web-based interactive PBPK (iPBPK) framework to facilitate its application. This iPBPK framework serves as a proof-of-concept for further improvements in the future and it can be applied to develop new models for other drugs in other food animal species, thereby facilitating the application of PBPK modeling in WDI estimation and food safety assessment.

Pharmacokinetics of 14 C-ortho-phenylphenol following intravenous administration in pigs.

Workers in the USA are exposed to industrial formulations, which may be toxic. These formulations often contain preservatives or biocides such as ortho-phenylphenol (OPP). There are limited data describing OPP following intravenous administration to assess truly the clearance of this chemical in humans and other species. In vivo experiments were conducted in pigs to determine related pharmacokinetic parameters. 14 C-OPP was administered as an intravenous bolus dose. Blood, feces, urine and tissue samples were collected for analysis by liquid scintillation. Data were analyzed using non-compartmental and compartmental pharmacokinetic model approaches. These data fitted a three-compartment model and showed that the half-life of 14 C-OPP following the intravenous bolus in pigs was 46.26 ± 10.01 h. The kidneys play a crucial role in clearance of 14 C-OPP with a large percentage of the dose being found in the urine (70.3 ± 6.9% dose). Comparisons with other species suggest that 14 C-OPP clearance in pigs (2.48 ml h-1 kg-1 ) is less than that in humans (18.87 ml h-1 kg-1 ) and rats (35.51 ml h-1 kg-1 ). Copyright © 2016 John Wiley & Sons, Ltd.

Assessment of penetrant and vehicle mixture properties on transdermal permeability using a mixed effect pharmacokinetic model of ex vivo porcine skin.

The accurate prediction of the rate and extent of transdermal absorption from topical exposure to chemical mixtures would be beneficial in risk assessment and drug delivery applications. The isolated perfused porcine skin flap (IPPSF) has been used as an ex vivo model for assessing transdermal absorption from topical exposures. A mixed effect, pharmacokinetic tissue model was used to model finite dose, transdermal, absorption data from IPPSF experiments for 12 penetrants dosed in up to 10 different vehicles. The model was able to identify permeability constant, while accounting for between and within unit variability, across the entire data set. This approach provides a platform for exploring the relationship between covariates (chemical descriptors and functions thereof) and the model parameters. Successive models were employed that reduced the overall variability in the parameter estimate by modeling the parameters as functions of the covariates. Log kp was initially modeled as a function of LogP and MW of the pure penetrant (adjusted r2  = 0.48). The addition of mixture factors to account for the different dosing vehicles further improved the relationship: to r2  = 0.56 with Connolly molecular area (CMA) and r2  = 0.78 with the further addition of total polar surface area difference (TPSAd). The pharmacokinetic model and quantitative structure property relationship (QSPR) developed for the IPPSF may be relevant to clinical transdermal formulation development. Copyright © 2016 John Wiley & Sons, Ltd.

Quantification of vehicle mixture effects on in vitro transdermal chemical flux using a random process diffusion model.

The effect of vehicle mixtures on transdermal permeation has been studied using transient flux profiles from porcine skin flow through diffusion cells. Such data characteristically exhibit a large amount of variability between treatments (vehicle and penetrant combinations) as well as noise within treatments. A novel mathematical model has been used that describes longitudinal variation as a time varying diffusivity. Between treatment variability was described by a mixed effects model. A quantitative structure property relationship (QSPR) was developed to describe the effects of the penetrant and vehicle mixture properties on the mean diffusivity and partition coefficient in the membrane. The relationship included terms for the logP and molecular weight of the penetrant and the refractive index of the vehicle mixture with R(2)>0.95 for K and >0.9 for partition coefficient (as K⋅D). This analysis improved on previous work, finding a more parsimonious model with higher predictability, while still identifying the mixture refractive index as a key descriptor in predicting vehicle effects. The concordance with established and expected relationships lends confidence to this new methodology for evaluating transient, finite dose, transdermal flux data collected using traditional experimental methods.

Development of a mixed-effect pharmacokinetic model for vehicle modulated in vitro transdermal flux of topically applied penetrants.

Transient flux profiles from in vitro flow-through cell experiments exhibit different characteristics depending upon the properties of the penetrants and vehicle mixtures applied. To enable discrimination of the chemical properties contributing to these differences, a consistent mathematical model should first be developed. A mixed effects modeling framework was used so that models can be estimated with as few parameters as possible, while also quantifying variability and accounting for correlation in the data. The models account for diffusion and binding within the membrane as well as dynamics on the diffusion coefficient. The models explain key features of the data, such as: lag time, sharp peaks in flux, two terminal phases, and low flux profiles. The models with dynamic diffusivity fit the data better than those without-particularly the sharp peaks. The significance of changing diffusivity over time suggests that vehicle effects are transient and are more accurately estimated when dynamics are modeled.