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1.  Chronically Implanted Pressure Sensors: Challenges and State of the Field 
Sensors (Basel, Switzerland)  2014;14(11):20620-20644.
Several conditions and diseases are linked to the elevation or depression of internal pressures from a healthy, normal range, motivating the need for chronic implantable pressure sensors. A simple implantable pressure transduction system consists of a pressure-sensing element with a method to transmit the data to an external unit. The biological environment presents a host of engineering issues that must be considered for long term monitoring. Therefore, the design of such systems must carefully consider interactions between the implanted system and the body, including biocompatibility, surgical placement, and patient comfort. Here we review research developments on implantable sensors for chronic pressure monitoring within the body, focusing on general design requirements for implantable pressure sensors as well as specifications for different medical applications. We also discuss recent efforts to address biocompatibility, efficient telemetry, and drift management, and explore emerging trends.
doi:10.3390/s141120620
PMCID: PMC4279503  PMID: 25365461
implantable pressure sensors; implantable pressure transducers; biocompatibility; telemetry; drift
2.  Impact of Osmotically Active Excipients on Bioavailability and Bioequivalence of BCS Class III Drugs 
The AAPS Journal  2013;15(4):1043-1050.
doi:10.1208/s12248-013-9509-z
PMCID: PMC3787221  PMID: 23868749
BCS; bioavailability/bioequivalence; drug absorption; excipient; osmotic potential
3.  International Guidelines for Bioequivalence of Systemically Available Orally Administered Generic Drug Products: A Survey of Similarities and Differences 
The AAPS Journal  2013;15(4):974-990.
The objective of this article is to discuss the similarities and differences among bioequivalence approaches used by international regulatory authorities when reviewing applications for marketing new generic drug products which are systemically active and intended for oral administration. We focused on the 13 jurisdictions and organizations participating in the International Generic Drug Regulators Pilot. These are Australia, Brazil, Canada, China, Chinese Taipei, the European Medicines Association, Japan, Mexico, Singapore, South Korea, Switzerland, the USA, and the World Health Organization. We began with a comparison of how the various jurisdictions and organizations define a generic product and its corresponding reference product. We then compared the following bioequivalence approaches: recommended bioequivalence study designs, method of pharmacokinetic calculations and bioequivalence acceptance limits, recommendations for modifying bioequivalence study designs and limits for highly variable drugs and narrow therapeutic index drugs, provisions for waiving bioequivalence study requirements (granting biowaivers), and implementation of the Biopharmaceutics Classification System. We observed that, overall, there are more similarities than differences in bioequivalence approaches among the regulatory authorities surveyed.
doi:10.1208/s12248-013-9499-x
PMCID: PMC3787230  PMID: 23821352
bioequivalence; biopharmaceutics classification system; biowaivers; generic drugs; regulatory authority
4.  Batch-to-Batch Quality Consistency Evaluation of Botanical Drug Products Using Multivariate Statistical Analysis of the Chromatographic Fingerprint 
AAPS PharmSciTech  2013;14(2):802-810.
Botanical drug products have batch-to-batch quality variability due to botanical raw materials and the current manufacturing process. The rational evaluation and control of product quality consistency are essential to ensure the efficacy and safety. Chromatographic fingerprinting is an important and widely used tool to characterize the chemical composition of botanical drug products. Multivariate statistical analysis has showed its efficacy and applicability in the quality evaluation of many kinds of industrial products. In this paper, the combined use of multivariate statistical analysis and chromatographic fingerprinting is presented here to evaluate batch-to-batch quality consistency of botanical drug products. A typical botanical drug product in China, Shenmai injection, was selected as the example to demonstrate the feasibility of this approach. The high-performance liquid chromatographic fingerprint data of historical batches were collected from a traditional Chinese medicine manufacturing factory. Characteristic peaks were weighted by their variability among production batches. A principal component analysis model was established after outliers were modified or removed. Multivariate (Hotelling T2 and DModX) control charts were finally successfully applied to evaluate the quality consistency. The results suggest useful applications for a combination of multivariate statistical analysis with chromatographic fingerprinting in batch-to-batch quality consistency evaluation for the manufacture of botanical drug products.
doi:10.1208/s12249-013-9966-9
PMCID: PMC3665986  PMID: 23636818
botanical drug products; chromatographic fingerprint; manufacturing process; multivariate statistical analysis; quality consistency
5.  Generic Development of Topical Dermatologic Products, Part II: Quality by Design for Topical Semisolid Products 
The AAPS Journal  2013;15(3):674-683.
The emergence of quality by design as a relatively new systematic science and risk-based approach has added a new dimension to pharmaceutical development and manufacturing. This review attempts to discuss the quality by design elements and concepts applied for topical semisolid products. Quality by design begins with defining a quality target product profile as well as critical quality attributes. Subsequently, this is followed by risk identification/risk analysis/risk evaluation to recognize critical material attributes and critical process parameters, in conjunction with design of experiments or other appropriate methods to establish control strategies for the drug product. Several design-of-experiment examples are included as practical strategies for the development and optimization of formulation and process for topical drug products.
doi:10.1208/s12248-013-9472-8
PMCID: PMC3691439  PMID: 23572241
dermatologic product; generic; quality by design; semisolid; topical product
6.  Application of Quality by Design to the Process Development of Botanical Drug Products: A Case Study 
AAPS PharmSciTech  2013;14(1):277-286.
This paper was designed to assess the value of quality by design (QbD) to improve the manufacturing process understanding of botanical drug products. Ethanol precipitation, a widely used unit operation in the manufacture of botanical drug products was employed to illustrate the use of QbD, taking the process of danshen (the dry root of Salvia miltiorrhiza Bunge) as an example. The recovery of four active pharmaceutical ingredients (APIs) and the removal of saccharides were used to represent the performance of ethanol precipitation. Potentially critical variables, including density of concentrate, ethanol consumption, and settling temperature were identified through risk assessment methods. Design of experiments (DOE) was used to evaluate the effects of the potentially critical factors on the performance of ethanol precipitation. It was observed that higher density of concentrate leads to higher removal of saccharides, but results in lower recovery of APIs. With the rise of ethanol consumption, the recovery of different APIs behaves in different ways. A potential design space of ethanol precipitation operation was established through DOE studies. The results in this work facilitate the enhanced understanding of the relationships between multiple factors (material attributes and process parameters) and the performance of ethanol precipitation. This case study demonstrated that QbD is a powerful tool to develop manufacturing process of botanical drug products.
doi:10.1208/s12249-012-9919-8
PMCID: PMC3581681  PMID: 23297167
botanical drug products; design of experiments (DOE); design space; ethanol precipitation; quality by design (QbD)
7.  Generic Development of Topical Dermatologic Products: Formulation Development, Process Development, and Testing of Topical Dermatologic Products 
The AAPS Journal  2012;15(1):41-52.
This review presents considerations which can be employed during the development of a semi-solid topical generic product. This includes a discussion on the implementation of quality by design concepts during development to ensure the generic drug product has similar desired quality attributes to the reference-listed drug (RLD) and ensure batch to batch consistency through commercial production. This encompasses the concept of reverse-engineering to copy the RLD as a strategy during product development to ensure qualitative (Q1) and quantitative (Q2) formulation similarity, as well as similarity in formulation microstructure (Q3). The concept of utilizing in vitro skin permeation studies as a tool to justify formulation differences between the test generic product and the RLD to ensure a successful pharmacodynamic or clinical endpoint bioequivalence study is discussed. The review concludes with a discussion on drug product evaluation and quality tests as well as in vivo bioequivalence studies.
doi:10.1208/s12248-012-9411-0
PMCID: PMC3535108  PMID: 23054971
dermatologic product; generic; semi-solid; topical product; quality by design
8.  Use of Partial Area under the Curve Metrics to Assess Bioequivalence of Methylphenidate Multiphasic Modified Release Formulations 
The AAPS Journal  2012;14(4):925-926.
doi:10.1208/s12248-012-9397-7
PMCID: PMC3475859  PMID: 22976173
attention deficit hyperactivity disorder; bioequivalence; generic drugs; methylphenidate; pAUC
9.  Implementation of a Reference-Scaled Average Bioequivalence Approach for Highly Variable Generic Drug Products by the US Food and Drug Administration 
The AAPS Journal  2012;14(4):915-924.
Highly variable (HV) drugs are defined as those for which within-subject variability (%CV) in bioequivalence (BE) measures is 30% or greater. Because of this high variability, studies designed to show whether generic HV drugs are bioequivalent to their corresponding HV reference drugs may need to enroll large numbers of subjects even when the products have no significant mean differences. To avoid unnecessary human testing, the US Food and Drug Administration’s Office of Generic Drugs developed a reference-scaled average bioequivalence (RSABE) approach, whereby the BE acceptance limits are scaled to the variability of the reference product. For an acceptable RSABE study, an HV generic drug product must meet the scaled BE limit and a point estimate constraint. The approach has been implemented successfully. To date, the RSABE approach has supported four full approvals and one tentative approval of HV generic drug products.
doi:10.1208/s12248-012-9406-x
PMCID: PMC3475857  PMID: 22972221
bioequivalence; generic drugs; highly variable drugs; reference-scaled average bioequivalence; US Food and Drug Administration
10.  Statistics on BCS Classification of Generic Drug Products Approved Between 2000 and 2011 in the USA 
The AAPS Journal  2012;14(4):664-666.
The Biopharmaceutics Classification system (BCS) classifies drug substances based on aqueous solubility and intestinal permeability. The objective of this study was to use the World Health Organization Model List of Essential Medicines to determine the distribution of BCS Class 1, 2, 3, and 4 drugs in Abbreviated New drug Applications (ANDA) submissions. To categorize solubility and intestinal permeability properties of generic drugs under development, we used a list of 61 drugs which were classified as BCS 1, 2, 3, and 4 drugs with certainty in the World Health Organization Model List of Essential Medicines. Applying this list to evaluation of 263 ANDA approvals of BCS drugs during the period of 2000 to 2011 indicated 110 approvals (41.8%) for Class 1 drugs (based on both biowaiver and in vivo bioequivalence studies), 55 (20.9%) approvals for Class 2 drugs, 98 (37.3%) approvals for Class 3 drugs, and no (0%) approvals for Class 4 drugs. The present data indicated a trend of more ANDA approvals of BCS Class 1 drugs than Class 3 or Class 2 drugs. Antiallergic drugs in Class 1, drugs for pain relief in Class 2 and antidiabetic drugs in Class 3 have received the largest number of approvals during this period.
doi:10.1208/s12248-012-9384-z
PMCID: PMC3475853  PMID: 22718306
ANDA; BCS biowaiver; bioequivalence; Biopharmaceutics Classification System; generic drug product
11.  Physicochemical Characterization of Complex Drug Substances: Evaluation of Structural Similarities and Differences of Protamine Sulfate from Various Sources 
The AAPS Journal  2012;14(3):619-626.
The purpose of this study was to characterize and evaluate differences of protamine sulfate, a highly basic peptide drug, obtained from five different sources, using orthogonal thermal and spectroscopic analytical methods. Thermogravimetric analysis and modulated differential scanning calorimetry showed that all five protamine sulfate samples had different moisture contents and glass transition and melting temperatures when temperature was modulated from 25 to 270°C. Protamine sulfate from source III had the highest residual moisture content (4.7 ± 0.2%) at 105°C, resulting in the lowest glass transition (109.7°C) and melting (184.2°C) temperatures compared with the other four sources. By Fourier-transform infrared (FTIR) spectroscopy, the five sources of protamine sulfate had indistinguishable spectra, and the spectra were consistent with a predominantly random coil conformation in solution and a minor population in a β-sheet conformation (~12%). Circular dichroism spectropolarimetry confirmed the FTIR results with prominent minima at 206 nm observed for all five sources. Finally, proton (1H) nuclear magnetic resonance spectroscopy showed that all five protamine sulfate sources had identical spectra with backbone amide chemical shifts between 8.20 and 8.80 ppm, consistent with proteins with predominantly random coil conformation. In conclusion, thermal analyses showed differences in the thermal behavior of the five sources of protamine sulfate, while spectroscopic analyses showed the samples had a predominantly random coil conformation with a small amount of β-sheet present.
doi:10.1208/s12248-012-9375-0
PMCID: PMC3385841  PMID: 22678712
circular dichroism; differential scanning calorimetry; Fourier-transform infrared spectroscopy; nuclear magnetic resonance; peptide; protamine sulfate; thermogravimetric analysis
12.  Endogenous MHC-Related Protein 1 Is Transiently Expressed on the Plasma Membrane in a Conformation That Activates Mucosal-Associated Invariant T Cells 
The development of mucosal-associated invariant T (MAIT) cells is dependent upon the class Ib molecule MHC-related protein 1 (MR1), commensal bacteria, and a thymus. Furthermore, recent studies have implicated MR1 presentation to MAIT cells in bacteria recognition, although the mechanism remains undefined. Surprisingly, however, surface expression of MR1 has been difficult to detect serologically, despite ubiquitous detection of MR1 transcripts and intracellular protein. In this article, we define a unique mAb capable of stabilizing endogenous mouse MR1 at the cell surface, resulting in enhanced mouse MAIT cell activation. Our results demonstrated that under basal conditions, endogenous MR1 transiently visits the cell surface, thus reconciling the aforementioned serologic and functional studies. Furthermore, using this approach, double-positive thymocytes, macrophages, and dendritic cells were identified as potential APCs for MAIT cell development and activation. Based on this pattern of MR1 expression, it is intriguing to speculate that constitutive expression of MR1 may be detrimental for maintenance of immune homeostasis in the gut and/or detection of pathogenic bacteria in mucosal tissues.
doi:10.4049/jimmunol.1003254
PMCID: PMC3618670  PMID: 21402896
13.  Applications of Human Pharmacokinetic Prediction in First-in-Human Dose Estimation 
The AAPS Journal  2012;14(2):262-281.
Quantitative estimations of first-in-human (FIH) doses are critical for phase I clinical trials in drug development. Human pharmacokinetic (PK) prediction methods have been developed to project the human clearance (CL) and bioavailability with reasonable accuracy, which facilitates estimation of a safe yet efficacious FIH dose. However, the FIH dose estimation is still very challenging and complex. The aim of this article is to review the common approaches for FIH dose estimation with an emphasis on PK-guided estimation. We discuss 5 methods for FIH dose estimation, 17 approaches for the prediction of human CL, 6 methods for the prediction of bioavailability, and 3 tools for the prediction of PK profiles. This review may serve as a practical protocol for PK- or pharmacokinetic/pharmacodynamic-guided estimation of the FIH dose.
doi:10.1208/s12248-012-9332-y
PMCID: PMC3326168  PMID: 22407287
allometric scaling; FIH dose; in vitro–in vivo correlations; pharmacokinetics; prediction
14.  The Use of BDDCS in Classifying the Permeability of Marketed Drugs1 
Pharmaceutical research  2008;25(3):483-488.
We recommend that regulatory agencies add the extent of drug metabolism (i.e., ≥90% metabolized) as an alternate method in defining Class 1 marketed drugs suitable for a waiver of in vivo studies of bioequivalence. That is, ≥90% metabolized is an additional methodology that may be substituted for ≥90% absorbed. We propose that the following criteria be used to define ≥ 90% metabolized for marketed drugs: Following a single oral dose to humans, administered at the highest dose strength, mass balance of the Phase 1 oxidative and Phase 2 conjugative drug metabolites in the urine and feces, measured either as unlabeled, radioactive labeled or nonradioactive labeled substances, account for ≥ 90% of the drug dosed. This is the strictest definition for a waiver based on metabolism. For an orally administered drug to be ≥ 90% metabolized by Phase 1 oxidative and Phase 2 conjugative processes, it is obvious that the drug must be absorbed. This proposal, which strictly conforms to the present ≥90% criteria, is a suggested modification to facilitate a number of marketed drugs being appropriately assigned to Class 1.
doi:10.1007/s11095-007-9523-x
PMCID: PMC3580995  PMID: 18236138
15.  Harmonization of Regulatory Approaches for Evaluating Therapeutic Equivalence and Interchangeability of Multisource Drug Products: Workshop Summary Report 
The AAPS Journal  2011;13(4):556-564.
Regulatory approaches for evaluating therapeutic equivalence of multisource (or generic) drug products vary among different countries and/or regions. Harmonization of these approaches may decrease the number of in vivo bioequivalence studies and avoid unnecessary drug exposure to humans. Global harmonization for regulatory requirements may be promoted by a better understanding of factors underlying product performance and expectations from different regulatory authorities. This workshop provided an opportunity for pharmaceutical scientists from academia, industry and regulatory agencies to have open discussions on current regulatory issues and industry practices, facilitating harmonization of regulatory approaches for establishing therapeutic equivalence and interchangeability of multisource drug products.
doi:10.1208/s12248-011-9294-5
PMCID: PMC3231855  PMID: 21845486
bioequivalence; harmonization; interchangeability; regulatory standards; therapeutic equivalence
16.  Dissolution Testing for Generic Drugs: An FDA Perspective 
The AAPS Journal  2011;13(3):328-335.
In vitro dissolution testing is an important tool used for development and approval of generic dosage forms. The objective of this article is to summarize how dissolution testing is used for the approval of safe and effective generic drug products in the United States (US). Dissolution testing is routinely used for stability and quality control purposes for both oral and non-oral dosage forms. The dissolution method should be developed using an appropriate validated method depending on the dosage form. There are several ways in which dissolution testing plays a pivotal role in regulatory decision-making. It may be used to waive in vivo bioequivalence (BE) study requirements, as BE documentation for Scale Up and Post Approval Changes (SUPAC), and to predict the potential for a modified-release (MR) drug product to dose-dump if co-administered with alcoholic beverages. Thus, in vitro dissolution testing plays a major role in FDA’s efforts to reduce the regulatory burden and unnecessary human studies in generic drug development without sacrificing the quality of the drug products.
doi:10.1208/s12248-011-9272-y
PMCID: PMC3160163  PMID: 21479700
bioequivalence; biopharmaceutics; generic drugs; in vitro dissolution; quality by design
17.  Utility of Physiologically Based Absorption Modeling in Implementing Quality by Design in Drug Development 
The AAPS Journal  2011;13(1):59-71.
To implement Quality by Design (QbD) in drug development, scientists need tools that link drug products properties to in vivo performance. Physiologically based absorption models are potentially useful tools; yet, their utility of QbD implementation has not been discussed or explored much in the literature. We simulated pharmacokinetics (PK) of carbamazepine (CBZ) after administration of four oral formulations, immediate-release (IR) suspension, IR tablet, extended-release (XR) tablet and capsule, under fasted and fed conditions and presented a general diagram of a modeling and simulation strategy integrated with pharmaceutical development. We obtained PK parameters and absorption scale factors (ASFs) by deconvolution of the PK data for IR suspension under fasted condition. The model was validated for other PK profiles of IR formulations and used to predict PK for XR formulations. We explored three key areas where a modeling and simulation approach impacts QbD. First, the model was used to help identify optimal in vitro dissolution conditions for XR formulations. Second, identification of critical formulations variables was illustrated by a parameter sensitivity analysis of mean particle radius for the IR tablet that showed a PK shift with decreased particle radius, Cmax was increased and Tmax was decreased. Finally, virtual trial simulations allowed incorporation of inter-subject variability in the model. Virtual bioequivalence studies performed for two test formulations suggested that an in vitro dissolution test may be a more sensitive discriminative method than in vivo PK studies. In summary, a well-validated predictive model is a potentially useful tool for QbD implementation in drug development.
Electronic supplementary material
The online version of this article (doi:10.1208/s12248-010-9250-9) contains supplementary material, which is available to authorized users.
doi:10.1208/s12248-010-9250-9
PMCID: PMC3032086  PMID: 21207216
advanced compartmental absorption and transit (ACAT) model; gastroplus™; modified release (MR); quality by design (QbD)
18.  Scientific Considerations for Generic Synthetic Salmon Calcitonin Nasal Spray Products 
The AAPS Journal  2010;13(1):14-19.
Under the Abbreviated New Drug Application pathway, a proposed generic salmon calcitonin nasal spray is required to demonstrate pharmaceutical equivalence and bioequivalence to the brand-name counterpart or the reference listed drug. This review discusses two important aspects of pharmaceutical equivalence for this synthetic peptide nasal spray product. The first aspect is drug substance sameness, in which a proposed generic salmon calcitonin product is required to demonstrate that it contains the same active ingredient as that in the brand-name counterpart. The second aspect is comparability in product- and process-related factors that may influence immunogenicity (i.e., peptide-related impurities, aggregates, formulation, and leachates from the container/closure system). The comparability of these factors helps to ensure the product safety, particularly with respect to immunogenicity. This review also highlights the key features of in vitro and/or in vivo studies for establishing bioequivalence for a solution nasal spray containing a systemically acting salmon calcitonin.
doi:10.1208/s12248-010-9242-9
PMCID: PMC3032093  PMID: 21052882
bioequivalence; generic; immunogenicity; nasal spray; pharmaceutical equivalence; salmon calcitonin
19.  Analysis of Bead Sizes for MR Capsules Labeled for Sprinkle 
AAPS PharmSciTech  2010;11(4):1508-1510.
The bead sizes used in approved modified release capsules labeled for sprinkling on food was investigated to generate bead size guidelines for generic products labeled for sprinkling. The conclusions from a survey of FDA databases were corroborated with experimental data obtained by measuring the bead sizes of several reference-listed drugs on the market labeled for administration by sprinkling on food. The experimental data show that majority of the marketed products were found to have bead sizes of less than 1,500 μm (1.5 mm). Based on this information, a bead size of less than 1,500 μm should generally be considered acceptable for use in generic products labeled for sprinkling.
doi:10.1208/s12249-010-9529-2
PMCID: PMC3011084  PMID: 20936439
bead size; generic drugs; modified-release capsules; quality target product profile; sprinkle
20.  Challenges and Opportunities in Establishing Scientific and Regulatory Standards for Assuring Therapeutic Equivalence of Modified Release Products: Workshop Summary Report 
The AAPS Journal  2010;12(3):371-377.
Modified release products are complex dosage forms designed to release drug in a controlled manner to achieve desired efficacy and safety. Inappropriate control of drug release from such products may result in reduced efficacy or increased toxicity. This workshop provided an opportunity for pharmaceutical scientists from academia, industry, and regulatory agencies to discuss current industry practices and regulatory expectations for demonstrating pharmaceutical equivalence and bioequivalence of MR products, further facilitating the establishment of regulatory standards for ensuring therapeutic equivalence of these products.
doi:10.1208/s12248-010-9201-5
PMCID: PMC2895434  PMID: 20440588
bioequivalence; interchangeability; modified release; pharmaceutical equivalence; therapeutic equivalence
21.  In Vitro Considerations to Support Bioequivalence of Locally Acting Drugs in Dry Powder Inhalers for Lung Diseases 
The AAPS Journal  2009;11(3):414-423.
Dry powder inhalers (DPIs) are used to deliver locally acting drugs (e.g., bronchodilators and corticosteroids) for treatment of lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). Demonstrating bioequivalence (BE) for DPI products is challenging, primarily due to an incomplete understanding of the relevance of drug concentrations in blood or plasma to equivalence in drug delivery to the local site(s) of action. Thus, BE of these drug/device combination products is established based on an aggregate weight of evidence, which utilizes in vitro studies to demonstrate equivalence of in vitro performance, pharmacokinetic or pharmacodynamic studies to demonstrate equivalence of systemic exposure, and pharmacodynamic and clinical endpoint studies to demonstrate equivalence in local action. This review discusses key aspects of in vitro studies in supporting the establishment of BE for generic locally acting DPI products. These aspects include comparability in device resistance and equivalence in in vitro testing for single inhalation (actuation) content and aerodynamic particle size distribution.
doi:10.1208/s12248-009-9121-4
PMCID: PMC2758114  PMID: 19495991
bioequivalence (BE); dry powder inhaler (DPI); locally acting drugs; particle size distribution; single inhalation (actuation) content
22.  Mechanistic Approaches to Predicting Oral Drug Absorption 
The AAPS Journal  2009;11(2):217-224.
Modeling and simulation of oral drug absorption have been widely used in drug discovery, development, and regulation. Predictive absorption models are used to determine the rate and extent of oral drug absorption, facilitate lead drug candidate selection, establish formulation development strategy, and support the development of regulatory policies. This review highlights the development of recent drug absorption models including dispersion and compartmental models. The compartmental models include the compartmental absorption and transit model; Grass model; gastrointestinal transit absorption model; advanced compartmental absorption and transit model; and advanced dissolution, absorption, and metabolism model. Compared to the early absorption models, the above models developed or extended since the mid-1990s have demonstrated greatly improved predictive performance by accounting for multiple factors such as drug degradation, gastric emptying, intestinal transit, first-pass metabolism, and intestinal transport. For future model development, more heterogeneous features of the gastrointestinal tract (villous blood flow, metabolizing enzymes, and transporters), food effects, and drug–drug interactions should be fully characterized and taken into consideration. Moreover, predicting population inter- and intravariability in oral drug absorption can be useful and important for the evaluation of clinical safety and efficacy of drugs. Establishing databases and libraries that contain accurate pharmaceutical and pharmacokinetic information for commercialized and uncommercialized drugs may also be helpful for model development and validation.
doi:10.1208/s12248-009-9098-z
PMCID: PMC2691458  PMID: 19381841
advanced compartmental absorption and transit (ACAT) model; advanced dissolution, absorption, and metabolism (ADAM) model; compartmental model; dispersion model; oral drug absorption
24.  Evaluation of a Scaling Approach for the Bioequivalence of Highly Variable Drugs 
The AAPS Journal  2008;10(3):450-454.
Various approaches for evaluating the bioequivalence (BE) of highly variable drugs (CV ≥ 30%) have been debated for many years. More recently, the FDA conducted research to evaluate one such approach: scaled average BE. A main objective of this study was to determine the impact of scaled average BE on study power, and compare it to the method commonly applied currently (average BE). Three-sequence, three period, two treatment partially replicated cross-over BE studies were simulated in S-Plus. Average BE criteria, using 80–125% limits on the 90% confidence intervals for Cmax and AUC geometric mean ratios, as well as scaled average BE were applied to the results. The percent of studies passing BE was determined under different conditions. Variables tested included within subject variability, point estimate constraint, and different values for σw0, which is a constant set by the regulatory agency. The simulation results demonstrated higher study power with scaled average BE, compared to average BE, as within subject variability increased. At 60% CV, study power was more than 90% for scaled average BE, compared with about 22% for average BE. A σw0 value of 0.25 appears to work best. The results of this research project suggest that scaled average BE, using a partial replicate design, is a good approach for the evaluation of BE of highly variable drugs.
doi:10.1208/s12248-008-9053-4
PMCID: PMC2761698  PMID: 18726698
bioequivalence; highly variable drugs; scaled bioequivalence; simulations
25.  Summary Workshop Report: Bioequivalence, Biopharmaceutics Classification System, and Beyond 
The AAPS Journal  2008;10(2):373-379.
The workshop “Bioequivalence, Biopharmaceutics Classification System, and Beyond” was held May 21–23, 2007 in North Bethesda, MD, USA. This workshop provided an opportunity for pharmaceutical scientists to discuss the FDA guidance on the Biopharmaceutics Classification System (BCS), bioequivalence of oral products, and related FDA initiatives such as the FDA Critical Path Initiative. The objective of this Summary Workshop Report is to document the main points from this workshop. Key highlights of the workshop were (a) the described granting of over a dozen BCS-based biowaivers by the FDA for Class I drugs whose formulations exhibit rapid dissolution, (b) continued scientific support for biowaivers for Class III compounds whose formulations exhibit very rapid dissolution, (c) scientific support for a number of permeability methodologies to assess BCS permeability class, (d) utilization of BCS in pharmaceutical research and development, and (e) scientific progress in in vitro dissolution methods to predict dosage form performance.
doi:10.1208/s12248-008-9040-9
PMCID: PMC2751390  PMID: 18679807
bioavailability; bioequivalence; biopharmaceutics classification system (BCS); oral absorption; permeability; regulatory science; solubility

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