Comparison of WHO and US FDA biowaiver dissolution test conditions using bioequivalent doxycycline hyclate drug products.

OBJECTIVES: The dissolution characteristics of immediate-release doxycycline hyclate products with certified in-vivo bioequivalence to the innovator product were tested with a view to possible application of biowaiver-based approval. METHODS: Five products were tested using US Pharmacopeia Apparatus 2: Antodox 100 mg hard gelatin capsules, Doxycyclin AL 100 T tablets, Doxycyclin-ratiopharm 100 soft gelatin capsules, Doxycyclin STADA 100 mg tablets and Doxy-Wolff 100 mg tablets. Three compendial buffers were used as dissolution media: simulated gastric fluid without pepsin, pH 1.2, acetate buffer, pH 4.5, and simulated intestinal fluid without pancreatin, pH 6.8. Results were obtained at two paddle speeds recommended for biowaiver applications: 75 rpm (World Health Organization; WHO) and 50 rpm (US Food and Drug Administration; US FDA). KEY FINDINGS: The results for the tablets and hard gelatin capsules indicate that a paddle speed of 75 rpm is more representative than 50 rpm, since 75 rpm generates dissolution profiles corresponding more closely to the in-vivo profiles than those at 50 rpm. For evaluating soft gelatin capsule formulations with lipid fill, both US FDA and WHO methods were found to be over-discriminating. CONCLUSIONS: Bioequivalence of immediate-release doxycycline hyclate tablets and hard gelatin capsules, but not soft gelatin capsules, can be evaluated in vitro using the biowaiver dissolution test conditions specified by the WHO.

Whole-body physiologically based pharmacokinetic population modelling of oral drug administration: inter-individual variability of cimetidine absorption.

OBJECTIVES: Inter-individual variability of gastrointestinal physiology and transit properties can greatly influence the pharmacokinetics of an orally administered drug in vivo. To predict the expected range of pharmacokinetic plasma concentrations after oral drug administration, a physiologically based pharmacokinetic population model for gastrointestinal transit and absorption was developed and evaluated. METHODS: Mean values and variability measures of model parameters affecting the rate and extent of cimetidine absorption, such as gastric emptying, intestinal transit times and effective surface area of the small intestine, were obtained from the literature. Various scenarios incorporating different extents of inter-individual physiological variability were simulated and the simulation results were compared with experimental human study data obtained after oral cimetidine administration of four different tablets with varying release kinetics. KEY FINDINGS: The inter-individual variability in effective surface area was the largest contributor to absorption variability. Based on in-vitro dissolution profiles, the mean plasma cimetidine concentration-time profiles as well as the inter-individual variability could be well described for three cimetidine formulations. In the case of the formulation with the slowest dissolution kinetic, model predictions on the basis of the in-vitro dissolution profile underestimated the plasma exposure. CONCLUSIONS: The model facilitates predictions of the inter-individual pharmacokinetic variability after oral drug administration for immediate and extended-release formulations of cimetidine, given reasonable in-vitro dissolution kinetics.

Towards quantitative prediction of oral drug absorption.

Although several routes of administration can be considered for new drug entities, the oral route remains the most popular. To predict the in vivo performance of a drug after oral administration from in vitro data, it is essential that the factors limiting absorption can be modelled. Factors limiting oral drug absorption are typically slow and/or incomplete dissolution, formation of insoluble complexes and/or decomposition in the gastrointestinal lumen, poor net permeability and first-pass metabolism. Although many attempts have been made to make global forecasts of oral bioavailability based on a single parameter (ranging from the partition coefficient [logP] to the polar surface area), it is clear from the diversity of properties that can influence delivery of drugs via the oral route that such an approach can at best lead to a qualitative estimation. To predict in vivo performance in a more quantitative way, it is instead necessary to identify the extent to which each of the aforementioned factors can limit absorption, and then combine the information into a comprehensive model of the absorptive processes. Much progress has been made in the last 10 years on developing methods to pin down the extent to which each of the factors actually limits the absorption of a given compound and, concomitantly, physiological models have been evolved, which show promise in terms of being able to integrate the information generated about each of the individual limiting factors. This article attempts to summarize recent progress on the various fronts as a kind of 'progress report' towards quantitative prediction of oral drug absorption.

Designing biorelevant dissolution tests for lipid formulations: case example--lipid suspension of RZ-50.

Biorelevant dissolution test methods for lipid formulations of RZ-50, an experimental Roche compound, were developed and compared with standard compendial methods in terms of their in vivo predictability. Release of RZ-50, a poorly soluble weakly acidic drug, from lipid suspensions filled in soft gelatin capsules was studied in compendial and biorelevant media using the USP Apparatus 2 (paddle method) and the USP Apparatus 3 (Bio-Dis method). Pharmacokinetic data were obtained in dogs after oral administration of a single 2.5mg dose of RZ-50 soft gelatin capsules in the postprandial state. Level A IVIVC analysis and curve comparison of fraction drug dissolved vs. absorbed using the Weibull distribution were used to evaluate the in vitro methods in terms of their ability to fit the in vivo plasma profiles. Very low drug release was observed with the paddle method owing to poor dispersibility of the lipids in the dissolution media, whereas the Bio-Dis method hydrodynamics facilitated release of the drug by emulsifying the formulation in the medium. The best IVIVC was obtained using a dissolution medium representing fed gastric conditions in combination with the Bio-Dis method. Curve comparisons of the fraction drug absorbed and the fraction drug dissolved profiles based on Weibull distribution fits yielded similar results. The Bio-Dis/biorelevant in vitro method appears to be suitable for this type of lipid formulation.

Feasibility of biowaiver extension to biopharmaceutics classification system class III drug products: cimetidine.

BACKGROUND: The extension of biowaivers (drug product approval without a pharmacokinetic bioequivalence study) to drugs belonging to Class III of the Biopharmaceutics Classification System (BCS) is currently a subject of much discussion. OBJECTIVES: To assess the relationship between in vitro dissolution characteristics and in vivo absorption performance of immediate-release (IR) products containing cimetidine, a BCS Class III compound, in human subjects. To evaluate the feasibility and appropriateness of an extension of the biowaiver concept to BCS Class III compounds. STUDY DESIGN AND PARTICIPANTS: BCS-conform dissolution tests were carried out on ten marketed cimetidine products from Thailand and Germany, as well as cimetidine tablet formulations containing cimetidine 400mg manufactured by direct compression using methacrylate copolymer (Eudragit) RS PO) as a release-retarding agent to yield three batches with significantly different release profiles. Twelve healthy male subjects were enrolled in a randomised, open-label, single-dose schedule based on a five-way Williams' design balanced for carryover effects. Subjects received the following treatments, with 1-week washout periods between: (i) Tagamet 400mg tablet; (ii) 7.5% methacrylate copolymer cimetidine tablet; (iii) 15% methacrylate copolymer cimetidine tablet; (iv) 26% methacrylate copolymer cimetidine tablet; and (v) Tagamet (300 mg/ 2 mL) intravenous injection. The area under the plasma concentration-time curve from 0 to 12 hours (AUC(12)) and AUC from time zero to infinity (AUC(infinity)), peak plasma concentration (C(max)), absolute bioavailability (F) and mean residence time (MRT) were evaluated and statistically compared among formulations. In vitro-in vivo correlation (IVIVC) analysis was then applied to elucidate the overall absorption characteristics of each tablet formulation. RESULTS: The release properties of the ten marketed cimetidine products were shown to comply with current US FDA criteria for rapidly dissolving drug products. As expected, the in vitro dissolution profiles of the cimetidine tablets containing different percentages of methacrylate copolymer differed considerably from one another. However, in vivo results showed no significant difference in AUC(12), AUC(infinity), C(max) and F between the tablets manufactured with methacrylate copolymer and the innovator. The MRT values obtained from 26% methacrylate copolymer tablets were significantly longer than for the other two methacrylate copolymer formulations and the Tagamet tablets. Furthermore, IVIVC analysis showed that the 26% methacrylate copolymer tablets exhibited dissolution rate-limited absorption, whereas the other formulations showed permeability rate-limited absorption. CONCLUSION: The results of the present study indicated that the absorption of cimetidine from IR tablets is, in general, limited by permeability rather than dissolution. IVIVC analysis demonstrated that only when the release was deliberately retarded (tablets containing 26% methacrylate copolymer), did the dissolution represent the rate-limiting step to drug absorption. On the in vitro side, it seems that 85% dissolution within 30 minutes, as currently required by the US FDA Guidance, is more than sufficient to guarantee bioequivalence of IR cimetidine products. For cimetidine and other BCS Class III drugs with a similar intestinal absorption pattern, application of the biowaiver concept seems to present little risk of an inappropriate bioequivalence decision.

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.

Precipitation in the small intestine may play a more important role in the in vivo performance of poorly soluble weak bases in the fasted state: case example nelfinavir.

The aim of this study was to evaluate the utility of biorelevant dissolution tests coupled with in silico simulation technology to forecast in vivo bioperformance of poorly water-soluble bases, using nelfinavir mesylate as a model compound. An in silico physiologically based pharmacokinetic (PBPK) model for poorly water-soluble, weakly basic drugs was used to generate plasma profiles of nelfinavir by coupling dissolution results and estimates of precipitation with standard gastrointestinal (GI) parameters and the disposition pharmacokinetics of nelfinavir. In vitro dissolution of nelfinavir mesylate film-coated tablets was measured in biorelevant and compendial media. Drug precipitation in the small intestine was estimated from crystal growth theory. GI parameters (gastric emptying rate and fluid volume) appropriate to the dosing conditions (fasting and fed states) were used in the PBPK model. The disposition parameters of nelfinavir were estimated by fitting compartmental models to the in vivo oral PK data. The in vivo performance in each prandial state was simulated with the PBPK model, and predicted values for AUC and C(max) were compared to observed values. Dissolution results in FaSSIF-V2 and FeSSIF-V2, simulating the fasting and fed small intestinal conditions, respectively, correctly predicted that there would be a positive food effect for nelfinavir mesylate, but overestimated the food effect observed in healthy human volunteers. In order to better predict the food effect, an in silico PBPK simulation model using STELLA® software was evolved. Results with the model indicated that invoking drug precipitation in the small intestine is necessary to describe the in vivo performance of nelfinavir mesylate in the fasted state, whereas a good prediction under fed state conditions is obtained without assuming any precipitation. In vitro-in silico-in vivo relationships (IVISIV-R) may thus be a helpful tool in understanding the critical parameters that affect the oral absorption of poorly soluble weak bases.

The biowaiver procedure: its application to antituberculosis products in the WHO prequalification programme.

In 2005, the World Health Organization (WHO) proposed that provided an active pharmaceutical ingredient could meet certain criteria, bioequivalence could be evaluated with a set of laboratory tests, obviating the need for expensive and time-consuming pharmacokinetic studies in humans. The aim of this work was to determine whether this so-called "biowaiver" procedure can be applied to antituberculosis products. Antituberculosis products from the WHO Prequalification Programme, including three ethambutol, two isoniazid and one pyrazinamide product, were investigated. In vitro dissolution data for these products were generated according to the biowaiver method stipulated in the WHO Guidance, and the bioequivalence decision based on these data was compared with that based on the corresponding in vivo pharmacokinetic data. In no case was a "false positive" bioequivalence decision reached using the biowaiver procedure, that is, all products deemed bioequivalent according to the biowaiver methods also proved to be bioequivalent in the corresponding pharmacokinetic study. These findings open the way to a simplified method of ensuring bioequivalence of antituberculosis drug products, thereby improving access to high quality antituberculosis medicines for a greater number of patients.

Biorelevant in vitro dissolution testing of products containing micronized or nanosized fenofibrate with a view to predicting plasma profiles.

The ability of in vitro biorelevant dissolution tests to predict the in vivo performance of nanosized fenofibrate (Lipidil 145 ONE®) and microsized fenofibrate (Lipidil - Ter®) was evaluated in this study. In vitro dissolution was carried out using USP apparatus 2 (paddle method) with updated biorelevant media to simulate the pre- and postprandial states. Membrane filters with different pore sizes were evaluated for their ability to hold back undissolved, nanosized drug particles. It was shown that filters with pore sizes of 0.1 µm and 0.02 µm were able to separate molecularly dissolved drug from colloidal and undissolved particles. In vitro results obtained with a suitable filter were used to generate simulated plasma profiles in combination with two different models using STELLA® software: (a) under the assumption of no permeability restrictions to absorption and (b) under the assumption of a permeability restriction. The simulated plasma profiles were compared to in vivo data for the nanosized and the microsized formulation in the fasted and fed states. The first model approach resulted in good correlation for the microsized fenofibrate formulation, but the plasma profile of the formulation containing nanosized fenofibrate was overpredicted in the fasted state. The second model successfully correlated with in vivo data for both formulations, regardless of prandial state. Comparison of simulations with the two models indicates that in the fasted state, absorption of fenofibrate from the nanosized formulation is at least partly permeability-limited, while for the microsized formulation the dissolution of fenofibrate appears to be rate-determining.

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.

Analysis of nifedipine absorption from soft gelatin capsules using PBPK modeling and biorelevant dissolution testing.

Delayed absorption of nifedipine when administered as a 20 mg immediate release soft gelatin capsule to fasted volunteers has been reported. Physiologically based pharmacokinetic (PBPK) modeling and in vitro dissolution data were used to explore our hypothesis that at high doses of nifedipine it precipitates in the stomach. Plasma concentration-time profiles following different doses of nifedipine were simulated using commercial PBPK software and compared to in vivo data. In vitro dissolution tests were performed with Adalat 10 mg capsules in different volumes of fasted state simulated gastric fluid (FaSSGF). The discrepancy in plasma concentration-time profiles between the different nifedipine doses could be well simulated, assuming protracted dissolution for the 20 mg dose. Nifedipine release from one Adalat 10 capsule in 250 or 500 mL FaSSGF was completed within 15 min whereas when release from two capsules, corresponding to 20 mg nifedipine, was studied in 250 mL FaSSGF, a maximum of about 75% drug dissolved was observed after 15 min followed by a decline in the % dissolved to a final value of approximately 40%. Based on the in silico and in vitro results it can be concluded that the observed prolongation in nifedipine absorption following the 20 mg dose was likely caused by nifedipine precipitation in human stomach.

Application of biorelevant dissolution tests to the prediction of in vivo performance of diclofenac sodium from an oral modified-release pellet dosage form.

In vitro biorelevant dissolution tests enabling the prediction of in vivo performance of an oral modified-release (MR) dosage form were developed in this study. In vitro dissolution of MR diclofenac sodium pellets containing 100mg active ingredient was evaluated under simulated pre- and postprandial conditions using USP Apparatus 3 (reciprocating cylinder, Bio-Dis) and 4 (flow-through cell) and results compared with compendial methods using USP Apparatus 1 (basket) and 2 (paddle). In vivo, the effects of food on the absorption of diclofenac sodium from the pellet dosage form were investigated by administering the product to 16 healthy volunteers pre- and postprandially in a crossover-design study. The in vitro results were compared with the in vivo data by means of Level A in vitro-in vivo correlation (IVIVC) and Weibull distribution analysis. The compendial dissolution tests were not able to predict food effects. The biorelevant dissolution tests predicted correctly that the release (and hence absorption) of diclofenac sodium would be slower in the fed state than in the fasted state. No significant differences in extent of absorption due to changes in extent of release were predicted or observed. The results demonstrate good correlations between in vitro drug release and in vivo drug absorption in both pre- and postprandial states using the biorelevant dissolution test methods.

Prediction of food effects on the absorption of celecoxib based on biorelevant dissolution testing coupled with physiologically based pharmacokinetic modeling.

Since the rate-determining step to the intestinal absorption of poorly soluble drugs is the dissolution in the gastrointestinal (GI) tract, postprandial changes in GI physiology, in addition to any specific interactions between drug and food, are expected to affect the pharmacokinetics and bioavailability of such drugs. In this study, in vitro dissolution testing using biorelevant media coupled with in silico physiologically based pharmacokinetic (PBPK) modeling was applied to the prediction of food effects on the absorption of a poorly soluble drug, celecoxib, from 200mg capsules. A PBPK model was developed based on STELLA software using dissolution kinetics, solubility, standard GI parameters and post-absorptive disposition parameters. Solubility, dissolution profiles and initial dissolution rate from celecoxib 200mg capsules were measured in biorelevant and compendial media. Standard GI parameters (gastric emptying rate and fluid volume) were varied according to the dosing conditions. Disposition parameters were estimated by fitting compartmental models to the oral PK data, since intravenous data are not available for celecoxib. Predictions of food effects and average plasma profiles were evaluated using the AUC and C(max) and the difference factor (f(1)). An approximately 7-fold difference in the maximum percentage dissolved was observed in in vitro dissolution tests designed to represent the fed and fasted states. By contrast, the food effect estimated by simulating the plasma profiles with the PBPK model predicted only a slight delay in the peak plasma level ( approximately 1h), and modest increases in the C(max) and AUC of approximately 1.9-fold and 1.3-fold in the fed state, respectively. The PBPK approach, combining in silico simulation coupled with biorelevant dissolution test results, thus corresponds much better to the food effect observed for celecoxib in vivo. Additionally, point estimates of AUC and C(max) as well as f(1) calculations demonstrated clear advantages of using results in biorelevant rather than compendial media in the PBPK model.

Dissolution media simulating conditions in the proximal human gastrointestinal tract: an update.

PURPOSE: The aim of this study was to update the compositions of biorelevant media to represent the composition and physical chemical characteristics of the gastrointestinal fluids as closely as possible while providing physical stability during dissolution runs and short-term storage. METHODS: Media were designed to reflect postprandial conditions in the stomach and proximal small intestine in the "early", "middle", and "late" phases of digestion. From these "snapshot" media, general media for simulating postprandial conditions were devised. Additionally, media reflecting preprandial conditions in the stomach and small intestine were revisited. RESULTS: A set of four media is presented. A recently published medium to represent the fasted stomach, FaSSGF, needed no further revision. To simulate the postprandial stomach, a new medium, FeSSGF, is presented. Media representing the upper small intestine in the fed and fasted states were fine-tuned according to physicochemical and biochemical characteristics in vivo. All four media proved to be stable under ambient storage conditions for at least 72 h as well as under usual dissolution test conditions. CONCLUSIONS: The updated dissolution media can be used to predict formulation performance and food effects in vivo. These media are more physiologically relevant and show better physical stability than their corresponding predecessors.

Convenient and rapid determination of cimetidine in human plasma using perchloric acid-mediated plasma protein precipitation and high-performance liquid chromatography.

This study demonstrates the analysis of cimetidine in human plasma with HPLC using a simplified sample preparation by protein precipitation with perchloric acid. Plasma cimetidine concentration was determined by plotting peak height ratio of cimetidine to ranitidine (internal standard, IS) against cimetidine concentrations in plasma. The cimetidine and ranitidine peaks were completely separated and no interference from plasma was observed. The lower limit of quantification (LLOQ) of the method was established at 0.1 microg/mL with a precision of 4.3% and a relative error of 1.9%. The average analytical recovery was >90% over the range of cimetidine concentrations (0.1-15.0 microg/mL). The linearity of calibration curve was excellent (r(2) > 0.999). The within- and between-day precision and accuracy, expressed as the coefficients of variation and relative error, were found to be less than 5%. Compared with previously reported methods, the analytical technique for cimetidine determination in human plasma presented here demonstrates comparable accuracy and precision, an acceptable analysis time, shorter and simpler sample preparation, and a reduced need for complicated equipment. The method presented here is simple and rapid, and the precision and sensitivity are appropriate for the determination of cimetidine in plasma in pharmacokinetic studies.