Biorelevant dissolution testing to predict the plasma profile of lipophilic drugs after oral administration

Identification of key factors affecting the oral absorption of salts of lipophilic weak acids: a case example

Objectives

Evaluate the ability of biorelevant media to adequately predict solubility in human gastrointestinal aspirates collected in the fasted state for the sodium salt of a highly dosed, Biopharmaceutics Classification System II (BCS II) compound with weakly acidic properties (L-870,810, pKa 7.3, HA (5-(1,1-dioxothiazinan-2-yl)-N-((4-fluorophenyl)methyl)-8-hydroxy-1,6-naphthyridine-7-carboxamide)). Identify key luminal processes that dictate the behaviour of sodium salt of HA (NaA), after single-dose administrations of high (relatively to solubility limit) doses corresponding to 400 and 800 mg of HA in the fasted state.

Methods

Aspirates from stomach and upper small intestine were collected from eight healthy fasted adults, after administration of 240 ml of water. Solubilities of NaA and HA were measured in aspirated samples and biorelevant media. Dissolution experiments of NaA granules were performed in biorelevant media. Prediction of oral pharmacokinetics was evaluated in silico using Stella software.

Key findings

Equilibrium solubility of NaA in fluids aspirated from the upper gastrointestinal tract is more transient than of HA. Solubility in upper gastrointestinal lumen was adequately estimated by data in biorelevant media. Supersaturation, followed by precipitation, which did not fully revert to the equilibrium solubility of HA, was observed during the dissolution of NaA granules in biorelevant media. Physiologically based pharmacokinetic modelling indicated that while intragastric processes had no significant impact on absorption kinetics, dissolution kinetics, kinetic solubility, radial transport rates and, for the 800-mg dose, precipitation kinetics in the small intestine had the greatest impact on absorption profiles.

Conclusions

Adequate prediction of the average plasma profile, after administration of NaA, required consideration of region-dependent dissolution rates and/or solubilisation.

Mechanism of chemical degradation and determination of solubility by kinetic modeling of the highly unstable sesquiterpene lactone nobilin in different media

The objective of this work was first to investigate the chemical degradation of the sesquiterpene lactone nobilin and determine its solubility under conditions of concurrent degradation for partially amorphous starting material; second, to determine the effect of biorelevant media used in the in vitro measurement of intestinal absorption on degradation and solubility of nobilin. Purely aqueous medium (aq-TMCaco ), fasted and fed state simulated intestinal fluid (FaSSIF-TMCaco and FeSSIF-TMCaco ), and two liposomal formulations (LiposomesFaSSIF and LiposomesFeSSIF ) with the same lipid concentration as FaSSIF-TMCaco and FeSSIF-TMCaco were used. Degradation products were identified by nuclear magnetic resonance and X-ray crystallography and the order of reaction kinetics was determined. Solubility was deduced with a mathematical model encompassing dissolution, degradation, and reprecipitation kinetics that took into account particle size distribution of the solid material. Degradation mechanism of nobilin involved water-catalyzed opening of the lactone ring and transannular cyclization resulting in five degradation products. Degradation followed first-order kinetics in aq-TMCaco and FaSSIF-TMCaco , and higher-order kinetics in FeSSIF-TMCaco and the two liposomal formulations, whereas degradation in the latter media was diminished. Solubility of nobilin increased in the order: aq-TMCaco < FaSSIF-TMCaco , < LiposomesFaSSIF < FeSSIF-TMCaco < LiposomesFeSSIF . Improvement of stability and solubility was consistent with the incorporation of the nobilin molecule into colloidal lipid particles. The developed kinetic model is proposed to be a useful tool for deducing solubility under dynamic conditions.

Paediatric oral biopharmaceutics: key considerations and current challenges

The complex process of oral drug absorption is influenced by a host of drug and formulation properties as well as their interaction with the gastrointestinal environment in terms of drug solubility, dissolution, permeability and pre-systemic metabolism. For adult dosage forms the use of biopharmaceutical tools to aid in the design and development of medicinal products is well documented. This review considers current literature evidence to guide development of bespoke paediatric biopharmaceutics tools and reviews current understanding surrounding extrapolation of adult methodology into a paediatric population. Clinical testing and the use of in silico models were also reviewed. The results demonstrate that further work is required to adequately characterise the paediatric gastrointestinal tract to ensure that biopharmaceutics tools are appropriate to predict performance within this population. The most vulnerable group was found to be neonates and infants up to 6 months where differences from adults were greatest.

Self-microemulsifying drug delivery system (SMEDDS)--challenges and road ahead

Self-microemulsifying drug delivery system (SMEDDS) has emerged as a vital strategy to formulate poor water soluble compounds for bioavailability enhancement. However, certain limitations are associated with SMEDDS formulations which include in vivo drug precipitation, formulation handling issues, limited lymphatic uptake, lack of predictive in vitro tests and oxidation of unsaturated fatty acids. These limitations restrict their potential usage. Inclusion of polymers or precipitation inhibitors within lipid based formulations helps to maintain drug supersaturation after dispersion. This, thereby, improves the bioavailability and reduces the variability on exposure. Also, formulating solid SMEDDS helps to overcome liquid handling and stability problems. Usage of medium chain triglycerides (MCT) and suitable antioxidants to minimize oxidation of unsaturated fatty acids are few of the steps to overcome the limitations associated with SMEDDS. The review discussed here, in detail, the limitations of SMEDDS and suitable measures that can be taken to overcome them.

Predicting the oral pharmacokinetic profiles of multiple-unit (pellet) dosage forms using a modeling and simulation approach coupled with biorelevant dissolution testing: case example diclofenac sodium

The objective of this research was to characterize the dissolution profile of a poorly soluble drug, diclofenac, from a commercially available multiple-unit enteric coated dosage form, Diclo-Puren® capsules, and to develop a predictive model for its oral pharmacokinetic profile. The paddle method was used to obtain the dissolution profiles of this dosage form in biorelevant media, with the exposure to simulated gastric conditions being varied in order to simulate the gastric emptying behavior of pellets. A modified Noyes-Whitney theory was subsequently fitted to the dissolution data. A physiologically-based pharmacokinetic (PBPK) model for multiple-unit dosage forms was designed using STELLA® software and coupled with the biorelevant dissolution profiles in order to simulate the plasma concentration profiles of diclofenac from Diclo-Puren® capsule in both the fasted and fed state in humans. Gastric emptying kinetics relevant to multiple-units pellets were incorporated into the PBPK model by setting up a virtual patient population to account for physiological variations in emptying kinetics. Using in vitro biorelevant dissolution coupled with in silico PBPK modeling and simulation it was possible to predict the plasma profile of this multiple-unit formulation of diclofenac after oral administration in both the fasted and fed state. This approach might be useful to predict variability in the plasma profiles for other drugs housed in multiple-unit dosage forms.

PBPK models for the prediction of in vivo performance of oral dosage forms

Drug absorption from the gastrointestinal (GI) tract is a highly complex process dependent upon numerous factors including the physicochemical properties of the drug, characteristics of the formulation and interplay with the underlying physiological properties of the GI tract. The ability to accurately predict oral drug absorption during drug product development is becoming more relevant given the current challenges facing the pharmaceutical industry. Physiologically-based pharmacokinetic (PBPK) modeling provides an approach that enables the plasma concentration-time profiles to be predicted from preclinical in vitro and in vivo data and can thus provide a valuable resource to support decisions at various stages of the drug development process. Whilst there have been quite a few successes with PBPK models identifying key issues in the development of new drugs in vivo, there are still many aspects that need to be addressed in order to maximize the utility of the PBPK models to predict drug absorption, including improving our understanding of conditions in the lower small intestine and colon, taking the influence of disease on GI physiology into account and further exploring the reasons behind population variability. Importantly, there is also a need to create more appropriate in vitro models for testing dosage form performance and to streamline data input from these into the PBPK models. As part of the Oral Biopharmaceutical Tools (OrBiTo) project, this review provides a summary of the current status of PBPK models available. The current challenges in PBPK set-ups for oral drug absorption including the composition of GI luminal contents, transit and hydrodynamics, permeability and intestinal wall metabolism are discussed in detail. Further, the challenges regarding the appropriate integration of results from in vitro models, such as consideration of appropriate integration/estimation of solubility and the complexity of the in vitro release and precipitation data, are also highlighted as important steps to advancing the application of PBPK models in drug development. It is expected that the "innovative" integration of in vitro data from more appropriate in vitro models and the enhancement of the GI physiology component of PBPK models, arising from the OrBiTo project, will lead to a significant enhancement in the ability of PBPK models to successfully predict oral drug absorption and advance their role in preclinical and clinical development, as well as for regulatory applications.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Coupling biorelevant dissolution methods with physiologically based pharmacokinetic modelling to forecast in-vivo performance of solid oral dosage forms

Objectives

To summarize the basis for and progress with the development of in-vitro–in-silico–in-vivo (IV-IS-IV) relationships for oral dosage forms using physiologically based pharmacokinetic (PBPK) modelling, with the focus on predicting the performance of solid oral dosage forms in humans.

Key findings

Various approaches to forecasting oral absorption have been reported to date. These range from simple dissolution tests, through biorelevant dissolution testing and laboratory simulations of the gastrointestinal (GI) tract, to the use of PBPK modelling to predict oral drug absorption based on the physicochemical parameters of the drug substance. Although each of these approaches can be useful for qualitative predictions, forecasting oral absorption on a quantitative basis with an individual approach is only possible for selected drug/dosage form combinations. By integrating biorelevant dissolution test results with the PBPK models, it has become possible to achieve quantitatively accurate as well as qualitative predictions of plasma profiles after oral dosing for both immediate and modified release formulations.

Summary

With further refinement of both the biorelevant dissolution testing methods and the PBPK models, it should be possible to expedite the development and regulatory approval of optimized dosage forms and dosing conditions.

Analysis of the enhanced oral bioavailability of fenofibrate lipid formulations in fasted humans using an in vitro-in silico-in vivo approach

Lipid-based formulations have established a significant role in the formulation of poorly soluble drugs for oral administration. In order to better understand their potential advantages over solid oral dosage forms, we studied the solubility and dissolution/precipitation characteristics of three self-microemulsifying drug delivery system (SMEDDS) formulations and one suspension of micronized fenofibrate in lipid excipients, for which pharmacokinetic studies had already been reported in the open literature. The in vitro dispersion/dissolution studies were carried out in biorelevant media using USP II apparatus. These were followed up by in silico simulations using STELLA® software, in which not only dispersion/dissolution, but also the precipitation and re-dissolution of fenofibrate was taken into account. While unformulated drug exhibited poor solubility (0.22 μg/mL in FaSSGF and 4.31 μg/mL in FaSSIF-V2(PO4)) and dissolved less than 2% in dissolution tests, the solubility of fenofibrate in the presence of the lipid excipients increased dramatically (e.g., to 65.44 μg/mL in the presence of the Myritol 318/TPGS/Tween 80 SMEDDS) and there was an attendant increase in the dissolution (over 80% from capsules containing the Myritol 318/TPGS/Tween 80 SMEDDS and about 20% from the dispersion of fenofibrate in lipid excipients). For the four lipid-based fenofibrate formulations studied, combining in vitro data in biorelevant media with in silico simulation resulted in accurate prediction of the in vivo human plasma profiles. The point estimates of C(max) and AUC ratio calculated from the in silico and in vivo plasma profiles fell within the 0.8-1.25 range for the SMEDDS solution and capsule formulations, suggesting an accurate simulation of the in vivo profiles. This similarity was confirmed by calculation of the respective f2 factors. Sensitivity analysis of the simulation profiles revealed that the SMEDDS formulations had virtually removed any dependency of absorption on the dissolution rate in the small intestine, whereas for the dispersion in lipid excipients, this barrier remained. Such results pave the way to optimizing the performance of oral lipid-based formulations via an in vitro-in silico-in vivo approach.

Case studies for practical food effect assessments across BCS/BDDCS class compounds using in silico, in vitro, and preclinical in vivo data

Practical food effect predictions and assessments were described using in silico, in vitro, and/or in vivo preclinical data to anticipate food effects and Biopharmaceutics Classification System (BCS)/Biopharmaceutics Drug Disposition Classification System (BDDCS) class across drug development stages depending on available data: (1) limited in silico and in vitro data in early discovery; (2) preclinical in vivo pharmacokinetic, absorption, and metabolism data at candidate selection; and (3) physiologically based absorption modeling using biorelevant solubility and precipitation data to quantitatively predict human food effects, oral absorption, and pharmacokinetic profiles for early clinical studies. Early food effect predictions used calculated or measured physicochemical properties to establish a preliminary BCS/BDDCS class. A rat-based preclinical BCS/BDDCS classification used rat in vivo fraction absorbed and metabolism data. Biorelevant solubility and precipitation kinetic data were generated via animal pharmacokinetic studies using advanced compartmental absorption and transit (ACAT) models or in vitro methods. Predicted human plasma concentration-time profiles and the magnitude of the food effects were compared with observed clinical data for assessment of simulation accuracy. Simulations and analyses successfully identified potential food effects across BCS/BDDCS classes 1-4 compounds with an average fold error less than 1.6 in most cases. ACAT physiological absorption models accurately predicted positive food effects in human for poorly soluble bases after oral dosage forms. Integration of solubility, precipitation time, and metabolism data allowed confident identification of a compound's BCS/BDDCS class, its likely food effects, along with prediction of human exposure profiles under fast and fed conditions.

Aqueous solubility: simple predictive methods (in silico, in vitro and bio-relevant approaches)

Aqueous solubility is a key physicochemical attribute required for the characterisation of an active pharmaceutical ingredient (API) during drug discovery and beyond. Furthermore, aqueous solubility is highly important for formulation selection and subsequent development processes. This review provides a summary of simple predictive methods used to assess aqueous solubility as well as an assessment of the more complex in silico methodologies and a review of the recent solubility challenge. In addition, a summary of experimental methods to determine solubility is included, with a discussion of some potential pitfalls.

Integrating drug permeability with dissolution profile to develop IVIVC

In this review article, three different approaches to predict in vivo oral absorption based on the in vitro data of drug permeability, solubility and dissolution were introduced. At the drug discovery stage, the absorption potential of each candidate is most important to select better compounds for further development. The concept of maximum absorbable dose is applied widely, not only to evaluate the absorption potential but also to elucidate the rate-limiting process of oral absorption that helps us to understand the cause of poor absorption. To integrate the permeability of the drug with its dissolution profile, two different approaches, in vitro dissolution/permeation system (D/P system) and in silico model and simulation method, are proposed. In the D/P system, by mimicking the in vivo process of drug absorption, the permeated amount of drugs, that is the total output of dissolution and permeation processes, are correlated with the fraction absorbed in human (F(a)). This system is powerful for evaluating the improved absorption by various formulations and the effect of food intake. On the other hand, in the model and simulation approach, an intrinsic dissolution parameter of drug particle, z, was extracted from the small scale in vitro test and the process of intestinal absorption was re-constructed in silico by incorporating the physiological parameters in human. The effective use of these approaches for the development of oral drug products is discussed through various case studies.

Predicting the oral absorption of a poorly soluble, poorly permeable weak base using biorelevant dissolution and transfer model tests coupled with a physiologically based pharmacokinetic model

For predicting food effects and simulating plasma profiles of poorly soluble drugs, physiologically based pharmacokinetic models have become a widely accepted tool in academia and the pharmaceutical industry. Up till now, however, simulations appearing in the open literature have mainly focused on BCS class II compounds, and many of these simulations tend to have more of a "retrospective" than a prognostic, predictive character. In this work, investigations on the absorption of a weakly basic BCS class IV drug, "Compound A", were performed. The objective was to predict the plasma profiles of an immediate release (IR) formulation of Compound A in the fasted and fed state. For this purpose, in vitro biorelevant dissolution tests and transfer model experiments were conducted. Dissolution and precipitation kinetics were then combined with in vivo post-absorptive disposition parameters using STELLA® software. As Compound A not only exhibits poor solubility but also poor permeability, a previously developed STELLA® model was revised to accommodate the less than optimal permeability characteristics as well as precipitation of the drug in the fasted state small intestine. Permeability restrictions were introduced into the model using an absorption rate constant calculated from the Caco-2 permeability value of Compound A, the effective intestinal surface area and appropriate intestinal fluid volumes. The results show that biorelevant dissolution tests are a helpful tool to predict food effects of Compound A qualitatively. However, the plasma profiles of Compound A could only be predicted quantitatively when the results of biorelevant dissolution test were coupled with the newly developed PBPK model.

Analytical methods for dissolution testing of nanosized drugs

OBJECTIVES

This mini-review describes the theoretical advantages of nanosizing drugs in terms of dissolution and the characterization of their behaviour with in-vitro dissolution testing.

KEY FINDINGS

It is shown that the increase in dissolution rate is not commensurate with common theories. The calculation of dissolution rate by surface area increase using the Nernst-Brunner equation is inappropriate since the diffusion layer, δ, cannot be assessed. These results highlight the importance of an appropriate experimental design to assess the dissolution rate in vitro, which will then serve as a building block for establishing in vitro-in vivo correlations. Several techniques to assess the amount of released drug in dissolution testing are discussed, some through a review of current literature (dialysis, turbidity measurement methods, fibre optics, asymmetrical flow-field-flow fractionation), some through experimental experience (ion-selective electrode and syringe filters). Further methods, such as microdialysis, ultrasonic resonance technology and centrifugal filter devices, are reviewed from literature with some additional data obtained in house. The techniques are further discussed with a view to coupling the results with simulation software tools such as STELLA© to predict the in-vivo behaviour of the drug. In doing so, it is necessary to generate experimental data on the dissolution rate, since this cannot be calculated directly from the surface increase of drug particles but rather depends on further factors such as the boundary layer thickness.

SUMMARY

It was concluded that syringe filters of appropriate pore size and the ion-selective electrode appear to be suitable for measurement of the dissolution rate of nanosized drugs.

Biorelevant in-vitro performance testing of orally administered dosage forms

Objectives

This review focuses on the evolution and current status of biorelevant media and hydrodynamics, and discusses the usefulness of biorelevant performance testing in the evaluation of specific dosage form related lumenal processes.

Key findings

During the last 15 years our knowledge of the gastrointestinal environment (including the lower gut) has improved dramatically and biorelevant media composition and, to a lesser extent, biorelevant hydrodynamics, have been refined. Biorelevant dissolution/release testing is useful for the evaluation of formulation and food effects on plasma levels after administration of immediate release dosage forms containing low solubility compounds and after administration of extended release products. Lumenal disintegration times of immediate release dosage forms and the bile acid sequestering activity of resins in the lumen can also be successfully forecasted with biorelevant in vitro testing.

Summary

Biorelevant in-vitro performance testing is an important tool for evaluating intralumenal dosage form performance. Since the formulation of new active pharmaceutical ingredients for oral delivery is more challenging than ever before, efforts to improve the predictability of biorelevant tests are expected to continue.

The effect of food on the oral bioavailability of drugs: a review of current developments and pharmaceutical technologies for pharmacokinetic control

Here we review the mediation of the food effects on drugs by pharmaceutical technologies. The pharmacokinetics of drugs are affected by the interaction of drugs with food, which changes drug physicochemical and physiological properties (food effects). Several pharmaceutical technologies may be used to control food effects. Drugs exhibit different patterns of solubilization depending on release formulations. Formulations such as nanoparticle, solid dispersion and cyclodextrin systems, may control the solubility and release of insoluble drugs. Other controlled-release technologies, such as osmotic-controlled release or colon-specific delivery systems may also control food effects. As the structure of drug candidates becomes more complex, different methods of investigation, such as in vitro and in vivo correlation and in silico simulation will be required to predict drug characteristics and food effects.

The dissolution test in biorelevant media as a prognostic tool for modeling of drug behavior in vivo

The review deals with the modern tool for modeling of drug behavior in vivo, - the dissolution test in biorelevant media, imitating gastrointestinal fluids. The formulations and preparation methods of fasted state simulation intestinal fluid, FaSSIF and fed state simulation intestinal fluid, FeSSIF, are defined. In addition, the dissolution characteristics of APIs from different BCS classes in biorelevant media are described. Possible applications of biorelevant media in regulatory practice and science are also shown.

Forecasting in vivo oral absorption and food effect of micronized and nanosized aprepitant formulations in humans

This study coupled results from biorelevant dissolution tests with in silico simulation technology to forecast in vivo oral absorption of micronized and nanosized aprepitant formulations in the pre- and post-prandial states. In vitro dissolution tests of the nanosized aprepitant formulation and micronized drug were performed in biorelevant and compendial media. An in silico physiologically based pharmacokinetic (PBPK) model was developed based on STELLA software using dissolution kinetics, standard gastrointestinal (GI) parameters and post-absorptive disposition parameters. GI parameters (gastric emptying rate and GI fluid volume) were varied according to the dosing conditions. Disposition parameters were estimated by fitting compartmental models to the in vivo oral PK data. Predictions of in vivo performance in each prandial state were evaluated using the AUC and C(max) generated from the simulated PK profiles. To predict oral absorption from the extremely fast dissolving nanosized aprepitant formulation, several variations on a previously published model were evaluated. Although models that assumed that the formulation behaved as an oral solution or that adjusted the dissolution kinetics according to the different numbers of particles per gram between micronized and nanosized aprepitant generated profiles similar to the observed in vivo data in the fed state, simulated profiles for the fasted state showed much faster absorption than that observed in the in vivo data. This appeared to result from the assumption of no absorption restrictions in those models. To better predict in vivo performance in both fasted and fed states, a model that adds permeability restrictions to absorption was applied. This model not only simulated the in vivo profiles for aprepitant well in both prandial states, but also predicted the dependency of the pharmacokinetics on the dose and the particle size of aprepitant. In conclusion, a model based on STELLA software combined with dissolution results in biorelevant media successfully forecasts the in vivo performance of both nanosized and micronized formulations of aprepitant in the fed and fasted states. Although dissolution is the primary limitation to the rate of absorption for micronized aprepitant, some permeability restrictions are revealed for the nanosized formulation. The results also indicate that biorelevant dissolution media have strong advantages over compendial media in forecasting the in vivo behavior of aprepitant.

The application of modified flow-through cell apparatus for the assessment of chlorhexidine dihydrochloride release from lozenges containing sorbitol

The objective of this work was to apply a new apparatus for the assay of the drug release from lozenge tablet with a potential use in the treatment of oral candidosis and another conditions connected to microbial etiopathology in the oral cavity or as an antiplaque factor. Also, an approach to comparison of the applied method with the classical paddle apparatus method was performed. Tablets containing chlorhexidine dihydrochloride were formulated with granulated sorbitol of different grades (diameter of 110, 180, 480, and 650 microm, respectively), lactose, and magnesium stearate as excipients. Tablets were obtained through direct compression, and uniformity of weight, friability, breaking strength, disintegration, and release rate were evaluated. The disintegration times ranged between 10 and 21 min. In the next stage of the study, the release of chlorhexidine from lozenges prepared with granulated sorbitol grade 110 microm and different amounts of lactose and magnesium stearate was assessed. Two stages were observed during the release of chlorhexidine dihydrochloride from the lozenges, assayed by the classical paddle apparatus method II USP. In the first stage, release rates were between 2.6 x 10(-2) and 4.7 x 10(-2) min(-1), in the second stage between 1.7 x 10(-3) and 7.7 x 10(-3) min(-1). In the case of the in-house method, the release was near to first-order kinetics through the entire release experiment, with rate constants between 3.6 x 10(-2) and 6.6 x 10(-2) min(-1). The sorbitol granulate of granules with diameter 110 microm was found to be most suitable for the lozenges with chlorhexidine dihydrochloride and lactose. The in-house release method, proposed in this work, seems to be more realistic for the preliminary assessment of predicted drug concentrations in the oral cavity after the intake of a lozenge.