Suitability of the dog as an animal model for evaluating theophylline absorption and food effects from different formulations

Usefulness of the Beagle Model in the Evaluation of Paracetamol and Ibuprofen Exposure after Oral Administration to Pediatric Populations: An Exploratory Study

The present study aimed to explore the usefulness of beagle dogs in combination with physiologically based pharmacokinetic (PBPK) modeling in the evaluation of drug exposure after oral administration to pediatric populations at an early stage of pharmaceutical product development. An exploratory, single-dose, crossover bioavailability study in six beagles was performed. A paracetamol suspension and an ibuprofen suspension were coadministered in the fasted-state conditions, under reference-meal fed-state conditions, and under infant-formula fed-state conditions. PBPK models developed with GastroPlus v9.7 were used to inform the extrapolation of beagle data to human infants and children. Beagle-based simulation outcomes were compared with published human-adult-based simulations. For paracetamol, fasted-state conditions and reference-meal fed-state conditions in beagles appeared to provide adequate information for the applied scaling approach. Fasted-state and/or reference-meal fed-state conditions in beagles appeared suitable to simulate the performance of ibuprofen suspension in pediatric populations. Contrary to human-adult-based translations, extrapolations based on beagle data collected under infant-formula fed-state conditions appeared less useful for informing simulations of plasma levels in pediatric populations. Beagle data collected under fasted and/or reference-meal fed-state conditions appeared to be useful in the investigation of pediatric product performance of the two investigated highly permeable and highly soluble drugs in the upper small intestine. The suitability of the beagle as a preclinical model to understand pediatric drug product performance under different dosing conditions deserves further evaluation with a broader spectrum of drugs and drug products and comparisons with pediatric in vivo data.

Bio-enabling strategies to mitigate the pharmaceutical food effect: a mini review

The concomitant administration of oral drugs with food can result in significant changes in bioavailability, leading to variable pharmacokinetics and considerable clinical implications, such as over- or under-dosing. Consequently, there is increasing demand for bio-enabling formulation strategies to reduce variability in exposure between the fasted and fed state and/or mitigate the pharmaceutical food effect. The current review critically evaluates technologies that have been implemented to overcome the positive food effects of pharmaceutical drugs, including, lipid-based formulations, nanosized drug preparations, cyclodextrins, amorphisation and solid dispersions, prodrugs and salts. Additionally, improved insight into preclinical models for predicting the food effect is provided. Despite the wealth of research, this review demonstrates that application of optimal formulation strategies to mitigate the positive food effects and the evaluation in preclinical models is not a universal approach, and improved standardisation of models to predict the food effects would be desirable. Ultimately, the successful reformulation of specific drugs to eliminate the food effect provides a panoply of advantages for patients with regard to clinical efficacy and compliance.

Invivo absorption behaviour of theophylline from starch-methyl methacrylate matrix tablets in beagle dogs

This study evaluates in vivo the drug absorption profiles from potato starch-methyl methacrylate matrices(*) using theophylline as a model drug. Healthy beagle dogs under fasting conditions were used for in vivo studies and plasma samples were analyzed by a fluorescence polarization immunoassay analysis (FPIA method). Non-compartmental and compartmental (population approach) analysis was performed to determine the pharmacokinetic parameters. The principle of superposition was applied to predict multiple dose plasma concentrations from experimental single dose data. An in vitro-in vivo correlation (IVIVC) was also assessed. The sustained absorption kinetics of theophylline from these formulations was demonstrated by comparison with two commercially available oral sustained-release theophylline products (Theo-Dur(®) and Theolair(®)). A one-compartment model with first order kinetics without lag-time best describes the absorption/disposition of theophylline from the formulations. Results revealed a theophylline absorption rate in the order FD-HSMMA≥Theo-Dur(®)≥OD-CSMMA>Theolair(®)≥FD-CSMMA. On the basis of simulated plasma theophylline levels, a twice daily dosage (every 12h) with the FD-CSMMA tablets should be recommended. A Level C IVIVC was found between the in vitrot50% and the in vivo AUC/D, although further optimization of the in vitro dissolution test would be needed to adequately correlate with in vivo data.

Predicting pharmacokinetics of drugs using physiologically based modeling--application to food effects

Our knowledge of the major mechanisms underlying the effect of food on drug absorption allows reliable qualitative prediction based on biopharmaceutical properties, which can be assessed during the pre-clinical phase of drug discovery. Furthermore, several recent examples have shown that physiologically based absorption models incorporating biorelevant drug solubility measurements can provide quite accurate quantitative prediction of food effect. However, many molecules currently in development have distinctly sub-optimal biopharmaceutical properties, making the quantitative prediction of food effect for different formulations from in vitro data very challenging. If such drugs reach clinical development and show undesirable variability when dosed with food, improved formulation can help to reduce the food effect and carefully designed in vivo studies in dogs can be a useful guide to clinical formulation development. Even so, such in vivo studies provide limited throughput for screening, and food effects seen in dog cannot always be directly translated to human. This paper describes how physiologically based absorption modeling can play a role in the prediction of food effect by integrating the data generated during pre-clinical and clinical research and development. Such data include physicochemical and in vitro drug properties, biorelevant solubility and dissolution, and in vivo pre-clinical and clinical pharmacokinetic data. Some background to current physiological absorption models of human and dog is given, and refinements to models of in vivo drug solubility and dissolution are described. These are illustrated with examples using GastroPlus to simulate the food effect in dog and human for different formulations of two marketed drugs.

Current methods for predicting human food effect

Food can impact the pharmacokinetics of a drug product through several mechanisms, including but not limited to, enhancement in drug solubility, changes in GI physiology, or direct interaction with the drug. Significant food effects complicate development of new drugs, especially when clinical plans require control and/or monitoring of food intake in relation to dosing. The prediction of whether a drug or drug product will show a human food effect is challenging. In vitro models which consider physical-chemical properties can classify the potential for a compound to demonstrate a positive, negative or no food effect, and may be appropriate for screening compounds at early stages of drug discovery. When comparing various formulations, dissolution tests in biorelevant media can serve as a predictor of human drug performance under fasted and fed conditions. Few in vivo models exist which predict the magnitude of change in pharmacokinetic parameters in humans when dosing in the presence of food, with the dog appearing to be the most studied species for this purpose. Control of gastric pH, as well as the amount and composition of the fed state in dogs are critical parameters to improving the predictability of the dog overall as a food effect model. No single universal model is applicable for all drugs at all stages of drug development. One or more models may be required depending whether the goal is to assess potential for a food effect, determine the magnitude of change in pharmacokinetic parameters in the fed/fasted state, or whether formulation efforts have the ability to mitigate an observed food effect.

Development and validation of a preclinical food effect model

A preclinical canine model capable of predicting a compound's potential for a human food effect was developed. The beagle dog was chosen as the in vivo model. A validation set of compounds with known propensities for human food effect was studied. Several diets were considered including high-fat dog food and various quantities of the human FDA meal. The effect of pentagastrin pretreatment was also investigated. The high-fat dog food did not predict human food effect and was discontinued from further evaluation. The amount of FDA meal in the dog was important in the overall prediction of the magnitude of human food effect. Fed/fasted Cmax and AUC ratios using a 50-g aliquot of the FDA meal in the dog were in the closest qualitative agreement to human data. Pentagastrin pretreatment did not affect the AUC in the fed state, but increased the fasted AUC for weakly basic compounds. Pentagastrin pretreatment and a 50-g aliquot of the FDA meal in the dog predicted the human food effect for a validation set of compounds. This model, which is intended for compound screening, will be helpful for determining food effect as a liability when compounds progress from discovery to clinical development.

A Multi‐mechanistic Drug Release Approach in a Bead Dosage Form and In Vivo Predictions

Our previous study has successfully prepared a combination of immediate release, enteric coated, and controlled release (CR) beads and mathematically modeled in vitro drug release characteristics of the combination based on the release profiles of individual beads. The objectives of the present study are to evaluate the combination and individual beads in vivo and to mathematically model in vivo drug input characteristics of the combination based on the in vivo input of individual beads. Beagle dogs were used as an animal model, and theophylline as a model drug. In vivo percent drug absorbed at different times (input function) after administration of a capsule bead dosage form was calculated using the Wagner-Nelson deconvolution method using intravenous injection of theophylline in each dog as a reference. The in vivo input functions of individual beads were each fitted to appropriate mathematical equations. The in vivo input function of the bead combination dosage form was calculated based on the individual mathematical equations (expected), and verified experimentally in vivo (experimental). The results showed that all bead dosage forms behave in vivo as defined in vitro. Enteric coated beads significantly delay the time to reach the maximum concentration of drug (tmax=4.9 h) compared to uncoated immediate release beads (2 h). The lag time of enteric coated beads is 1.1 h. CR beads showed both longer tmax (6 h) and mean residence time (MRT=9.7 h) compared to the uncoated immediate release beads (tmax=2 h and MRT=7.1 h) as designed in vitro. The in vivo input functions for the three individual beads can be fitted to equations as a function of square root of time. The combined bead dosage form showed tmax of 2.4 h and MRT of 7.9 h. The experimental and expected in vivo input profiles agreed to within +/- 12% (residues at individual data points). Our results suggest that the drug input function of a combined multi-mechanism oral dosage form can be predicted from the in vivo performance of individual formulations using the dog as an in vivo model.

The effect of polyion complex formation on in vitro/in vivo correlation of hydrophilic matrix tablets

The aim of this study was to investigate the effects of polyion complex formation on in vivo performance of hydrophilic matrix tablets. Three kinds of controlled release theophylline tablets were prepared by direct compression using carboxymethyldextran (CMD), a mixture of CMD and [2-(diethylamino)ethyl]dextran (EA), and a mixture of dextran sulfate (DS) and EA. According to a conventional dissolution test, in vitro drug release profiles of these tablets were similar to each other. In vivo absorption profiles of theophylline after oral administration to beagle dogs, however, were quite different and were not consistent with in vitro release profiles. Thus, we applied a modified in vitro release test considering destructive forces. An excellent in vitro/in vivo correlation was obtained in the cases of CMD/EA- and DS/EA-tablets. The results suggested that the drug was released constantly in the overall gastrointestinal tract, and even in the colon. Then, hydrophilic matrices were characterized by swelling rate, matrix density and strength in a wet state. DS/EA-tablets showed limited swelling, higher density and a larger value of wet strength than the others. These findings indicated that polyion complex formation in gel layer contributes to prevent over-swelling and strengthen the wetted matrices.

An adjusted pharmacokinetic equation for predicting drug levels in vivo based on in vitro square root of time release kinetics

An adjusted pharmacokinetic equation that predicts in vivo plasma drug profiles for controlled release (CR) dosage forms having square root of time drug release kinetics has been derived. The CR hydrogel tablets containing hydroxypropyl methylcellulose (HPMC) were formulated with theophylline and Fast Flo lactose, to produce tablets with HPMC K100MP content of 30% w/w. Plasma profiles in vivo were determined from four male beagle dogs. Tablet gel strength (gamma) was measured as previously reported. Results show drug release in vitro follows square root of time kinetics for the formulation in all media (purified H2O, 0.1 N HCl, and pH 6.8 phosphate buffer). The gamma values were not significantly different (p > 0.05) among the tablets in different dissolution media, with absolute values in DI H2O of 6600 erg/cm3, which is above the minimum threshold value of gamma (approximately 6000 erg/cm3) needed for acceptable in vitro/in vivo correlation. Comparison of predicted and observed plasma profiles in vivo, using the adjusted square root pharmacokinetic equation, showed a better fit of the overall pattern and absolute values of the in vivo data as compared to equations that assume first- or zero-order drug release from the HPMC based tablets. The adjusted square root pharmacokinetic equation can serve as a valuable aid in the design of formulations to yield a desired plasma profile in vivo and provides supporting evidence to the mechanism of drug release in vitro.

The effect of controlled release tablet performance and hydrogel strength on in vitro/in vivo correlation

The impact of controlled release (CR) formulations having different gel strength values (gamma) on in vivo tablet performance and the in vitro/in vivo correlation of the formulations was investigated. The CR tablets containing either hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), or carbomer were formulated with theophylline and Fast Flo lactose to produce tablets with a polymer content of 8 and 30% w/w. gamma was measured using a previously reported method. Male beagle dogs were utilized. Results showed that dissolution profiles were similar for all three polymers at the same % w/w level of polymer, irrespective of media (DI H2O, 0.1 N HCl, and pH 6.8 phosphate buffer). Mean gamma values were significantly different (p < or = 0.05) and were in order of HPMC K100MP > HPC HXF > carbomer 971P (same 30% w/w) with absolute gamma values at 30% w/w in DI H2O of 6600, 4600, and 1600 ergs/cm3, respectively. Drug profiles in plasma for the 30% HPMC K100MP tablets were consistent with in vitro dissolution profiles and gamma values. Plasma profiles for the 30% HPC HXF tablets were similar in vivo as the HPMC tablets. Plasma profiles for the 30% carbomer 971P formulation showed much higher drug concentrations (compared to HPMC and HPC) in vivo in all dogs. This findings is not consistent with the slow drug release found in the dissolution profiles but consistent with its low in vitro gamma values. Assessment of the predictability of a level A in vitro/in vivo correlation was quantified by absolute mean percent prediction error (PE). Formulations having gamma approximately 6000 ergs/cm3 have acceptable PE < 20%, and low standard deviation (sigma). Results showed that gamma values of CR hydrogel tablets in vitro will affect the in vivo performance (i.e., absorption kinetics of the drug) of the tablets and were also found to better assess (compared to in vitro dissolution profiles alone) the predictability of in vitro/in vivo correlations (level A and multiple level C).