Deconvolution and IVIVC: Exploring the Role of Rate-Limiting Conditions

In vitro-in vivo correlation (IVIVC) development for long-acting injectable drug products based on poly(lactide-co-glycolide)

In vitro-in vivo correlation (IVIVC), linking in vitro drug release to in vivo drug release or in vivo drug absorption, has been explored chiefly for oral extended-release dosage forms. Currently, there are no official guidelines on IVIVC development for non-oral drug delivery systems. Recently, many long-acting injectable (LAI) formulations based on poly(lactide-co-glycolide) (PLGA) have been developed to deliver various drugs, ranging from small molecules to peptides and proteins, for up to 6 months. The circumstances involved in the LAI formulations are drastically different from those in oral formulations, which generally deliver drugs for a maximum of 24 h. This article examines 37 IVIVC studies of PLGA microparticle formulations available in the literature. Understanding and establishing an IVIVC of LAI formulations requires more than merely plotting the percentage in vitro drug release against the percentage in vivo absorption. In vivo drug absorption (or release) should be measured to provide a complete pharmacokinetic profile when feasible. Accelerated in vitro release methods need to be respective of the real-time measurements by sharing the same release mechanism. Obtaining meaningful IVIVCs with predictive capability will be highly useful for future regulatory actions and for developing generic and new formulations.

Application of the Finite Absorption Time (F.A.T.) Concept in the Assessment of Bioequivalence

PURPOSE

Το formulate a methodology for the assessment of bioequivalence using metrics, which are based on the physiologically sound F.A.T.

CONCEPT

METHODS

The equations of the physiologically based finite time pharmacokinetic models for the one-and two-compartment model with one and two input stages of absorption were solved to derive metrics for the extent and rate of absorption. Simulated data were used to study the proper way for the estimation of metrics. A bioequivalence study was analyzed using these metrics.

RESULTS

The rate of drug absorption was found to be equal to the slope of the amount absorbed versus time curve. The amount of drug absorbed at the end of the absorption process, corresponding to the blood concentration at F.A.T. is an indicator of the extent of absorption. The plot of the ratio test/reference of the simulated data for the amount absorbed as a function of time becomes constant beyond the end of drug absorption from the formulation exhibiting the longer absorption. The assessment of the bioequivalence study was based on the slope of the amount absorbed versus time curve for the rate of absorption, while the estimate for the constant ratio test/reference for the amount absorbed was used for the assessment of extent of absorption.

CONCLUSIONS

The assessment of rate in bioequivalence studies can be based on the estimation of slope of the percent absorbed versus time curve while the constant ratio test/reference for the amount of drug absorbed is an indicator of the extent of absorption.

Revamping Biopharmaceutics-Pharmacokinetics with Scientific and Regulatory Implications for Oral Drug Absorption

PURPOSE

The Wagner-Nelson and Loo-Riegelman methods developed in the 1960s and used since for the construction of percent of drug absorbed as a function of time as well as in in vitro in vivo correlations are re-considered in the light of the physiologically sound Finite Absorption Time (F.A.T.) concept developed recently.

METHODS

The classical equations for the percentage of drug absorption as a function of time were modified by taking into account the termination of drug absorption at F.A.T., replacing the parameters associated with the assumption of infinite drug absorption.

RESULTS

Mathematical analysis using the relevant Physiologically Based Pharmacokinetic Finite Time (PBFTK) models assuming one- or two-compartment drug disposition, revealed that the modified %absorbed versus time curves are of bilinear type with an ascending limb intersecting the horizontal line at F.A.T. A computer-based methodology is described for the estimation of F.A.T. from experimental data. More than one linear ascending limb is found when more than one absorption phase is operating. Experimental data were analyzed and the estimates for F.A.T were found to be similar to those derived from nonlinear regression analysis using PBFTPK models.

CONCLUSION

These results place an end to the routinely reported exponential %absorbed versus time curves prevailing in biopharmaceutics-pharmacokinetics since their inception in the'60 s. These findings point to the use of the F.A.T. concept in drug absorption research and regulatory guidelines such as deconvolution techniques for the assessment of drug input rate, stochastic mean absorption time calculations, population analyses, in vitro in vivo correlations and bioequivalence guidelines.

Revisiting the in-vitro and in-vivo considerations for in-silico modelling of complex injectable drug products

Complex injectable drug products (CIDPs) have often been developed to modulate the pharmacokinetics along with efficacy for therapeutic agents used for remediation of chronic disorders. The effective development of CIDPs has exhibited complex kinetics associated with multiphasic drug release from the prepared formulations. Consequently, predictability of pharmacokinetic modelling for such CIDPs has been difficult and there is need for advanced complex computational models for the establishment of accurate prediction models for in-vitro-in-vivo correlation (IVIVC). The computational modelling aims at supplementing the existing knowledge with mathematical equations to develop formulation strategies for generation of predictable and discriminatory IVIVC. Such an approach would help in reduction of the burden of effect of hidden factors on preclinical to clinical translations. Computational tools like physiologically based pharmacokinetics (PBPK) modelling have combined physicochemical and physiological properties along with IVIVC characteristics of clinically used formulations. Such techniques have helped in prediction and understanding of variability in pharmacodynamic parameters of potential generic products to clinically used formulations like Doxil®, Ambisome®, Abraxane® in healthy and diseased population using mathematical equations. The current review highlights the important formulation characteristics, in-vitro, preclinical in-vivo aspects which need to be considered while developing a stimulatory predictive PBPK model in establishment of an IVIVC and in-vitro-in-vivo relationship (IVIVR).

Development of clindamycin loaded oral microsponges (Clindasponges) for antimicrobial enhancement: In vitro characterization and simulated in vivo studies

Clindamycin phosphate (CLP) is a broad-spectrum antibiotic that is used widely for different types of infections. It has a short half-life and hence it should be taken every six hours to ensure adequate antibiotic blood concentration. On the other hand, microsponges are extremely porous polymeric microspheres, offering the prolonged controlled release of the drug. The present study aims to develop and evaluate innovative CLP-loaded microsponges (named Clindasponges) to prolong and control the drug release and enhance its antimicrobial activity, consequently improving patient compliance. The clindasponges were fabricated successfully by quasi-emulsion solvent diffusion technique using Eudragit S100 (ES100) and ethyl cellulose (EC) as carriers at various drug-polymer ratios. Several variables were optimized for the preparation technique including the type of solvent, stirring time, and stirring speed. The clindasponges were then characterized in terms of particle size, production yield, encapsulation efficiency, scanning electron microscopy, FTIR spectroscopy analysis, in vitro drug release with kinetic modeling, and antimicrobial activity study. Moreover, in vivo, pharmacokinetics parameters of CLP from the candidate formula were simulated based on the convolution method and in vitro- in vivo correlation (IVIVC-Level A) was built up successfully. Uniform spherical microsponges with 82.3µm mean particle size with a porous spongy structure were evident. ES2 batch exhibited the highest production yield and encapsulation efficiency (53.75% and 74.57%, respectively) and it was able to exhaust 94% of the drug at the end of 8 hrs of the dissolution test. The release profile data of ES2 was best fitted to Hopfenberg kinetic model. ES2 was significantly (p< 0.05) effective against Staphylococcus aureus and Escherichia coli compared to the control. Also, ES2 displayed a twofold increase in the simulated AUC compared to the reference marketed product.

Elucidating the Particle Size Effect of Andrographolide Suspensions on Their IVIVC Performance in Oral Absorption

The study aimed to explore the size effect on the in vitro-in vivo correlation (IVIVC) in the oral absorption of andrographolide nanosuspensions (Ag-NS). Ag-NS with controllable particle sizes were prepared by ultrasonic dispersion method, and the formulation and process parameters were optimized through single factor experiments using mean particle size, polydispersity index, and stability as evaluation indicators. The morphology of Ag-NS was observed by scanning electron microscopy (SEM), and the crystalline state of the nanosuspensions was characterized by X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC). The dissolution tests were carried out with the paddle method in two different mediums simulating the pH conditions in intestinal fluid pH 6.8 and gastric fluid (pH 1.2), respectively. The pharmacokinetic behaviors were investigated in rats after oral administration, and a deconvolution approach was introduced to determine the correlation between in vitro dissolution and in vivo absorption (IVIVC). The formulation with the use of lecithin and PEG-800 as stabilizers showed its potential in the size-controllable preparation of Ag-NS. Via altering the ultrasonication amplitude and time, three Ag-NS suspensions with particle sizes of particle size, i.e., Ag-NS 250 (244.3 ± 0.4 nm), Ag-NS 450 (464.3 ± 32.2 nm), Ag-NS 1000 (1015 ± 36.1 nm) were prepared. Their morphological and crystal characteristics did not change during the size reduction process, but both of their in vitro dissolution and in vivo absorption were improved. Relatively better IVIVC performance was observed with the in vitro dissolution data at pH 6.8 (r > 0.9). With the reduction of particle size, the in vivo absorption fraction was more closed to the level of the in vitro dissolution. In conclusion, the decrease in particle size would improve the dissolution and absorption of Ag-NS, and also affect their IVIVC performance. The study would facilitate the design and quality control of Ag-NS in terms of particle size and dissolution specifications.

Pharmacokinetics of Levonorgestrel in Rat and Minipig and Pharmacokinetics of Etonogestrel in Rat Following Various Administration Routes

1. The objective of these studies was to determine the pharmacokinetics of levonorgestrel and etonogestrel in Sprague-Dawley rat or Göttingen minipig following various administration routes.2. Four sequential crossover studies were conducted: Study 1 administered levonorgestrel 30 µg intravenously and intradermally in four minipigs; Study 2 administered levonorgestrel 30 µg intravenously in 12 rats; Study 3 administered levonorgestrel 60 µg intravenously and subcutaneously in 12 rats; and Study 4 administered etonogestrel 30 µg intravenously in 12 rats. Samples were quantified using liquid chromatography-tandem mass spectrometry and pharmacokinetic parameters were estimated via noncompartmental analysis.3. C_max and AUC_inf for etonogestrel and levonorgestrel were similar following 30 µg intravenous bolus in rat, suggesting comparable pharmacokinetics. Levonorgestrel exposure was dose-proportional in rats, based on two-fold higher AUC_inf following levonorgestrel 60 versus 30 µg. Bioavailability of intradermal and subcutaneous levonorgestrel was 97.7% (Study 1) and 90.3% (Study 3), respectively. The minipig levonorgestrel clearance was 21.5 L/hr, which was about 10-fold higher than both the rat levonorgestrel (range: 0.985 to 1.45 L/hr) and etonogestrel clearance (range: 0.803 to 0.968 L/hr).4. These studies contribute to the gap in knowledge of nonclinical levonorgestrel and etonogestrel pharmacokinetics, which is necessary for ongoing development of long-acting reversible contraceptives.

Integration of advanced methods and models to study drug absorption and related processes: An UNGAP perspective

This collection of contributions from the European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) community assembly aims to provide information on some of the current and newer methods employed to study the behaviour of medicines. It is the product of interactions in the immediate pre-Covid period when UNGAP members were able to meet and set up workshops and to discuss progress across the disciplines. UNGAP activities are divided into work packages that cover special treatment populations, absorption processes in different regions of the gut, the development of advanced formulations and the integration of food and pharmaceutical scientists in the food-drug interface. This involves both new and established technical approaches in which we have attempted to define best practice and highlight areas where further research is needed. Over the last months we have been able to reflect on some of the key innovative approaches which we were tasked with mapping, including theoretical, in silico, in vitro, in vivo and ex vivo, preclinical and clinical approaches. This is the product of some of us in a snapshot of where UNGAP has travelled and what aspects of innovative technologies are important. It is not a comprehensive review of all methods used in research to study drug dissolution and absorption, but provides an ample panorama of current and advanced methods generally and potentially useful in this area. This collection starts from a consideration of advances in a priori approaches: an understanding of the molecular properties of the compound to predict biological characteristics relevant to absorption. The next four sections discuss a major activity in the UNGAP initiative, the pursuit of more representative conditions to study lumenal dissolution of drug formulations developed independently by academic teams. They are important because they illustrate examples of in vitro simulation systems that have begun to provide a useful understanding of formulation behaviour in the upper GI tract for industry. The Leuven team highlights the importance of the physiology of the digestive tract, as they describe the relevance of gastric and intestinal fluids on the behaviour of drugs along the tract. This provides the introduction to microdosing as an early tool to study drug disposition. Microdosing in oncology is starting to use gamma-emitting tracers, which provides a link through SPECT to the next section on nuclear medicine. The last two papers link the modelling approaches used by the pharmaceutical industry, in silico to Pop-PK linking to Darwich and Aarons, who provide discussion on pharmacometric modelling, completing the loop of molecule to man.

In vitro dissolution considerations associated with nano drug delivery systems

Nano drug delivery systems (NDDS) offer promising solution for the translation of future nanomedicines. As bioavailability and therapeutic outcomes can be improved by altering the drug release from these NDDS, it becomes essential to thoroughly understand their drug release kinetics. Moreover, U.S. Food and Drug Administration requires critical evaluation of potential safety, efficacy, and public health impacts of nanomaterials. Spiraling up market share of NDDS has also stimulated the pharmaceutical industry to develop their cost-effective generic versions after the expiry of patent and associated exclusivity. However, unlike the conventional dosage forms, the in vivo disposition of NDDS is highly intricate and different from their in vitro behavior. Significant challenges exist in the establishment of in vitro-in vivo correlation (IVIVC) due to incomplete understanding of nanoparticles' in vivo biofate and its impact on in vitro experimental protocols. A rational design of dissolution may serve as quality and quantity control tool and help develop a meaningful IVIVC for favorable economic implications. Clinically relevant drug product specifications (critical quality attributes) can be identified by establishing a link between in vitro performance and in vivo exposure. In vitro dissolution may also play a pivotal role to understand the dissolution-mediated clearance and safety of NDDS. Prevalent in vitro dissolution methods for NDDS and their limitations are discussed in this review, among which USP 4 is gaining more interest recently. Researchers are working diligently to develop biorelevant in vitro release assays to ensure optimal therapeutic performance of generic versions of these NDDS. This article focuses on these studies and presents important considerations for the future development of clinically relevant in vitro release methods. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

In vitro and in vivo correlation for lipid-based formulations: Current status and future perspectives

Lipid-based formulations (LBFs) have demonstrated a great potential in enhancing the oral absorption of poorly water-soluble drugs. However, construction of in vitro and in vivo correlations (IVIVCs) for LBFs is quite challenging, owing to a complex in vivo processing of these formulations. In this paper, we start with a brief introduction on the gastrointestinal digestion of lipid/LBFs and its relation to enhanced oral drug absorption; based on the concept of IVIVCs, the current status of in vitro models to establish IVIVCs for LBFs is reviewed, while future perspectives in this field are discussed. In vitro tests, which facilitate the understanding and prediction of the in vivo performance of solid dosage forms, frequently fail to mimic the in vivo processing of LBFs, leading to inconsistent results. In vitro digestion models, which more closely simulate gastrointestinal physiology, are a more promising option. Despite some successes in IVIVC modeling, the accuracy and consistency of these models are yet to be validated, particularly for human data. A reliable IVIVC model can not only reduce the risk, time, and cost of formulation development but can also contribute to the formulation design and optimization, thus promoting the clinical translation of LBFs.

Development, validation and application of physiologically based biopharmaceutics model to justify the change in dissolution specifications for DRL ABC extended release tablets

OBJECTIVE

The generic drug product DRL ABC is an Extended Release (ER) Tablet manufactured by Dr. Reddy's Laboratories Limited and have multi point dissolution as part of release specification. A proposal is being made to revise the dissolution specification and the aim of present work was to evaluate if this would still provide bioequivalent product.

METHODS

PBBM was developed for DRL ABC using literature reported pharmacokinetic (PK) data. The intravenous PK data and in vitro metabolic rate constants were utilized for developing PBPK model first, followed by that in conjugation with mechanistic ACAT^TM model, a PBBM is developed for per-oral immediate release formulations. The validated model was applied to predict clinical bioequivalence (BE) study data for the Reference (Innovator ER Tablet) and Test product. For Reference and Test product, in vivo dissolution profiles were mechanistically deconvoluted from plasma concentration (Cp)-time profiles. Further, mechanistic in vitro-in vivo relationship (IVIVR) applied to in vitro release profiles of two hypothetical Test product batches (one with single point low dissolution profile (SPLP) and other with overall low dissolution profile (LP)) in order to calculate their in vivo releases and population simulation was performed with 40 virtual subjects.

RESULTS

Results from the cross-over virtual trials showed BE between the Reference and various Test product batches (SPLP and LP), with maximum Cp (C_max) and area under the Cp-time curve (AUC_0-inf) well within 80-125% range.

CONCLUSION

PBBM in conjugation with IVIVR and virtual BE was successfully applied for justifying changes in dissolution specification of DRL ABC.

Screening of Bioequivalent Extended-Release Formulations for Metformin by Principal Component Analysis and Convolution-Based IVIVC Approach

Bioequivalence (BE) is usually hard to achieve for extended-release (ER) dosage form products due to not only its complicated formulation but also to the BCS classification of the investigated drugs. Considering the difficulties in establishing full-scale IVIVC and limited in vivo pharmacokinetics data in the early stage of formulation development, we have selected BCS III drug metformin as a model drug to demonstrate a novel approach for the selection of BE formulations. Firstly, dissolution tests in both standard and biorelevant media were performed followed by identification of the most similar formulation WM to the reference product (GXR) based on principal component analysis (PCA) of the dissolution data. Then, we developed an IVIVC model using the reported GXR pharmacokinetics profiles via a convolution-based approach. Based on our established IVIVC and in vitro dissolution profiles of generic metformin ER products, we were able to predict their in vivo pharmacokinetic profiles and quantitatively compare the differences in AUC and C_max to ensure the correct selection of BE product. Finally, the selection of WM as the BE formulation of GXR was confirmed with a pilot BE study in healthy volunteers under fasting state. Moreover, the in vivo data from the fed state study were further integrated into our IVIVC model to identify FeSSIF-V2 as the biorelevant media for WM. Our novel integrative approach of PCA with a convolution-based IVIVC was successfully adopted for the screening of the BE metformin ER formulation and such an approach could be further utilized for the effective selection of BE formulation for other drugs/formulations with complex in vivo absorption processes.

C. A. Hop C. Inter-individual and inter-regional variations in enteric drug metabolizing enzyme activities: Results with cryopreserved human intestinal mucosal epithelia (CHIM) from the small intestines of 14 donors

We have previously reported successful isolation and cryopreservation of human intestinal mucosa (CHIM) with retention of viability and drug metabolizing enzyme activities. Here we report the results of the quantification of drug metabolizing enzyme activities in CHIM from different regions of the small intestines from 14 individual donors. CHIM were isolated from the duodenum, jejunum, and ileum of 10 individuals, and from 10 consecutive 12-inch segments starting from the pyloric sphincter of human small intestines from four additional individuals. P450 and non-P450 drug metabolizing enzyme activities (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A, UGT, SULT, FMO, MAO, AO, NAT1, and NAT2) were quantified via incubation with pathway-selective substrates. Quantifiable activities were observed for all pathways except for CYP2A6. Comparison of the duodenum, jejunum, and ileum in 10 donors shows jejunum had higher activities for CYP2C9, CYP3A, UGT, SULT, MAO, and NAT1. Further definition of regional variations with CHIM from ten 12-inch segments of the proximal small intestine shows that the segments immediately after the first 12-inch segment (duodenum) had the highest activity for most of the drug metabolizing enzymes but with substantial differences among the four donors. Our overall results demonstrate that there are substantial individual differences in drug metabolizing enzymes and that jejunum, especially the regions immediately after the duodenum, had the highest drug metabolizing enzyme activities.

In Vitro Dissolution and in Silico Modeling Shortcuts in Bioequivalence Testing

Purpose: To review in vitro testing and simulation platforms that are in current use to predict in vivo performances of generic products as well as other situations to provide evidence for biowaiver and support drug formulations development. Methods: Pubmed and Google Scholar databases were used to review published literature over the past 10 years. The terms used were “simulation AND bioequivalence” and “modeling AND bioequivalence” in the title field of databases, followed by screening, and then reviewing. Results: A total of 22 research papers were reviewed. Computer simulation using software such as GastroPlus™, PK-Sim^® and SimCyp^® find applications in drug modeling. Considering the wide use of optimization for in silico predictions to fit observed data, a careful review of publications is required to validate the reliability of these platforms. For immediate release (IR) drug products belonging to the Biopharmaceutics Classification System (BCS) classes I and III, difference factor (ƒ₁) and similarity factor (ƒ₂) are calculated from the in vitro dissolution data of drug formulations to support biowaiver; however, this method can be more discriminatory and may not be useful for all dissolution profiles. Conclusions: Computer simulation platforms need to improve their mechanistic physiologically based pharmacokinetic (PBPK) modeling, and if prospectively validated within a small percentage of error from the observed clinical data, they can be valuable tools in bioequivalence (BE) testing and formulation development.

Mechanistic Deconvolution of Oral Absorption Model with Dynamic Gastrointestinal Fluid to Predict Regional Rate and Extent of GI Drug Dissolution

Multiple approaches such as mathematical deconvolution and mechanistic oral absorption models have been used to predict in vivo drug dissolution in the gastrointestinal (GI) tract. However, these approaches are often validated by plasma pharmacokinetic profiles, but not by in vivo drug dissolution due to the limited data available regarding the local GI environment. It is also challenging to predict and validate in vivo dissolution in different regions of the GI tract (stomach, duodenum, jejunum, and ileum). In this study, the dynamic fluid compartment absorption and transport (DFCAT) model was used to predict the in vivo dissolution profiles of ibuprofen, which was administered as an 800-mg immediate-release tablet to healthy subjects, in different regions of the GI tract. The prediction was validated with concentration time-courses of ibuprofen (BCS class 2a) in different regions of the GI tract that we have obtained over the past few years. The computational model predicted that the dissolution of ibuprofen was minimal in the stomach (2%), slightly more in the duodenum (6.3%), and primarily dissolved in the jejunum (63%) and the ileum (25%). The detailed model prediction of drug dissolution in different regions of GI can provide a quantitative reference of in vivo dissolution that may provide valuable insight in developing in vitro tests for drug product optimization and quality.

Bayesian knowledge integration for an in vitro-in vivo correlation model

The primary goal of "in vitro-in vivo correlation" (IVIVC) is the reliable prediction of the in vivo serum concentration-time course, based on the in vitro drug dissolution or release profiles. IVIVC methods are particularly appropriate for formulations that are released over an extended period of time or with a lag in absorption and may support approving a change in formulation of a drug without additional bioequivalence trials in human subjects. Most of the current IVIVC models are assessed using frequentist methods, such as linear regression, based on averaged data and entail complex and potentially unstable mathematical deconvolution. The proposed IVIVC approach includes (a) a nonlinear-mixed effects model for the in vitro release data; (b) a population pharmacokinetic (PK) compartment model for the in vivo immediate release (IR) data; and (c) a system of ordinal differential equations (ODEs), containing the submodels (a) and (b), which approximates and predicts the in vivo controlled release (CR) data. The innovation in this paper consists of splitting the parameter space between submodels (a) and (b) versus (c). Subsequently, the uncertainty on these parameters is accounted for using a Bayesian framework, that is estimates from the first two submodels serve as priors for the Bayesian hierarchical third submodel. As such, the Bayesian method explained ensures a natural integration and transfer of knowledge between various sources of information, balancing possible differences in sample size and parameter uncertainty of in vitro and in vivo studies. Consequently, it is a very flexible approach yielding results for a broad range of data situations. The application of the method is demonstrated for a transdermal patch (TD).

Defining level A IVIVC dissolution specifications based on individual in vitro dissolution profiles of a controlled release formulation

Regulatory guidelines recommend that, when a level A IVIVC is established, dissolution specification should be established using averaged data and the maximum difference between AUC and C_max between the reference and test formulations cannot be greater than 20%. However, averaging data assumes a loss of information and may reflect a bias in the results. The objective of the current work is to present a new approach to establish dissolution specifications using a new methodology (individual approach) instead of average data (classical approach). Different scenarios were established based on the relationship between in vitro-in vivo dissolution rate coefficient using a level A IVIVC of a controlled release formulation. Then, in order to compare this new approach with the classical one, six additional batches were simulated. For each batch, 1000 simulations of a dissolution assay were run. C_max ratios between the reference formulation and each batch were calculated showing that the individual approach was more sensitive and able to detect differences between the reference and the batch formulation compared to the classical approach. Additionally, the new methodology displays wider dissolution specification limits than the classical approach, ensuring that any tablet from the new batch would generate in vivo profiles which its AUC or C_max ratio will be out of the 0.8-1.25 range, taking into account the in vitro and in vivo variability of the new batches developed.

In vivo release of peptide-loaded PLGA microspheres assessed through deconvolution coupled with mechanistic approach

In this study, a reevaluation of the in vivo release phases from long-release PLGA-based microspheres is presented, leading to a better characterization of the plasma concentrations/time profile. Microspheres were designed for intramuscular injection releasing a cyclic somatostatin analog over 70 days. Clinical study was performed in 64 healthy subjects receiving a subcutaneous dose of an immediate release solution as reference formulation and an intramuscular injection of microspheres as test formulation. The in vivo input curve was obtained by numerical deconvolution. Results showed that double Weibull function could not fit correctly the tri-phasic (burst, lag, and erosion) in vivo input profile typical for PLGA-based formulations, due to a change in the drug release trend in the terminal phase. Triple Weibull showed a significant improvement in the curve fitting, each term being assigned to one of the following phases: initial (burst/lag), erosion, and terminal phase of drug release. The existence of the additional terminal phase was confirmed by a mechanistic approach as well, which denoted that this phase was, most probably, a consequence of the release mechanism change from erosion to diffusion controlled. The same model demonstrated that the burst release was as well influenced by the polymer swelling, while currently existing theories state that the burst phase is mainly determined by the dissolution of immediately available drug substance and diffusion through surface related pores.

Characterising Drug Release from Immediate-Release Formulations of a Poorly Soluble Compound, Basmisanil, Through Absorption Modelling and Dissolution Testing

The study aimed to characterise the mechanism of release and absorption of Basmisanil, a biopharmaceutics classification system (BCS) class 2 compound, from immediate-release formulations via mechanistic absorption modelling, dissolution testing, and Raman imaging. An oral absorption model was developed in GastroPlus® and verified with single-dose pharmacokinetic data in humans. The properties and drug release behaviour of different oral Basmisanil formulations were characterised via biorelevant dissolution and Raman imaging studies. Finally, an in vitro-in vivo correlation (IVIVC) model was developed using conventional and mechanistic deconvolution methods for comparison. The GastroPlus model accurately simulated oral Basmisanil exposure from tablets and granules formulations containing micronized drug. Absorption of oral doses below 200 mg was mostly dissolution rate-limited and thus particularly sensitive to formulation properties. Indeed, reduced exposure was observed for a 120-mg film-coated tablet and the slower dissolution rate measured in biorelevant media was attributed to differences in drug load. This hypothesis was confirmed when Raman imaging showed that the percolation threshold was exceeded in this formulation. This biorelevant dissolution method clearly differentiated between the formulations and was used to develop a robust IVIVC model. The study demonstrates the applicability and impact of mechanistic absorption modelling and biopharmaceutical in vitro tools for rational drug development.