Use of the Same Model or Modeling Strategy Across Multiple Submissions: Focus on Complex Drug Products

Evidence shows that there is an increasing use of modeling and simulation to support product development and approval for complex generic drug products in the USA, which includes the use of mechanistic modeling and model-integrated evidence (MIE). The potential for model reuse was the subject of a workshop session summarized in this review, where the session included presentations and a panel discussion from members of the U.S. Food and Drug Administration (FDA), academia, and the generic drug product industry. Concepts such as platform performance assessment and MIE standardization were introduced to provide potential frameworks for model reuse related to mechanistic models and MIE, respectively. The capability of models to capture formulation and product differences was explored, and challenges with model validation were addressed for drug product classes including topical, orally inhaled, ophthalmic, and long-acting injectable drug products. An emphasis was placed on the need for communication between FDA and the generic drug industry to continue to foster maturation of modeling and simulation that may support complex generic drug product development and approval, via meetings and published guidance from FDA. The workshop session provided a snapshot of the current state of modeling and simulation for complex generic drug products and offered opportunities to explore the use of such models across multiple drug products.

Drug Permeability - Best Practices for Biopharmaceutics Classification System (BCS)-Based Biowaivers: A workshop Summary Report

The workshop "Drug Permeability - Best Practices for Biopharmaceutics Classification System (BCS) Based Biowaivers" was held virtually on December 6, 2021, organized by the University of Maryland Center of Excellence in Regulatory Science and Innovation (M-CERSI), and the Food and Drug Administration (FDA). The workshop focused on the industrial, academic, and regulatory experiences in generating and evaluating permeability data, with the aim to further facilitate implementation of the BCS and efficient development of high-quality drug products globally. As the first international permeability workshop since the BCS based biowaivers was finalized as the ICH M9 guideline, the workshop included lectures, panel discussions, and breakout sessions. Lecture and panel discussion topics covered case studies at IND, NDA, and ANDA stages, typical deficiencies relating to permeability assessment supporting BCS biowaiver, types of evidence that are available to demonstrate high permeability, method suitability of a permeability assay, impact of excipients, importance of global acceptance of permeability methods, opportunities to expand the use of biowaivers (e.g. non-Caco-2 cell lines, totality-of-evidence approach to demonstrate high permeability) and future of permeability testing. Breakout sessions focused on 1) in vitro and in silico intestinal permeability methods; 2) potential excipient effects on permeability and; 3) use of label and literature data to designate permeability class.

Principles and Experimental Considerations for In Vitro Transporter Interaction Assays

Drug transporters are universally acknowledged as important determinants of the absorption, distribution, metabolism, and excretion of both endogenous and exogenous compounds. Altered transporter function, whether due to genetic polymorphism, DDIs, disease, or environmental factors such as dietary constituents, can result in changes in drug efficacy and/or toxicity due to changes in circulating or tissue levels of either drugs or endogenous substrates.Prediction of whether and to what extent the biological fate of a drug is influenced by drug transporters, therefore, requires in vitro test systems that can accurately predict the risk and magnitude of clinical DDIs. While these in vitro assessments appear simple in theory, practitioners recognize that there are multiple factors that can influence experimental outcomes. A better understanding of these variables, including test compound characteristics, test systems, assay formats, and experimental design, will enable clear, actionable steps and translatable outcomes that may avoid unnecessary downstream clinical engagement. This chapter will delineate the role of these variables in improving in vitro assay outcomes.

Public Workshop Summary Report on Fiscal Year 2021 Generic Drug Regulatory Science Initiatives: Data Analysis and Model-Based Bioequivalence

On May 4, 2020, the US Food and Drug Administration (FDA) hosted an online public workshop titled "FY 2020 Generic Drug Regulatory Science Initiatives Public Workshop" to provide an overview of the status of the science and research priorities and to solicit input on the development of Generic Drug User Fee Amendments fiscal year 2021 priorities. This report summarizes the podium presentations and the outcome of discussions along with innovative ways to overcome challenges and significant opportunities related to model-based approaches in bioequivalence assessment for breakout session 4 titled, "Data analysis and model-based bioequivalence (BE)." This session focused on the application of model-based approaches in the generic drug development, with a vision of accelerating regulatory decision making for abbreviated new drug application assessments. The session included both podium presentations and panel discussions with three topics of interest: (i) in vitro study evaluation methods and their clinical relevance, (ii) challenges in model-based BE, (iii) emerging expertise and tools in implementing new BE approaches.

Innovative in vitro methodologies for establishing therapeutic equivalence

To improve the quality of pharmaceutical products in their markets, several Latin American countries have begun to require that new generic products demonstrate bioequivalence against innovator or reference products. However, given the number of products involved, it is not feasible to rely on clinical studies to comply with this requirement. Instead, it makes sense to adopt or develop strategies that are appropriate to the characteristics of the region. To streamline drug development and accelerate patients' access to quality drug products, 15 years ago the United States Food and Drug Administration (FDA) decided to grant exemptions from clinical bioequivalence studies (i.e., biowaivers) for certain types of drug products based on the Biopharmaceutics Classification System (BCS). Biowaivers can significantly reduce development time and cost and can also prevent unnecessary human exposure to potentially dangerous drugs while providing a robust, consistent standard for therapeutic equivalence of generic drug products. In addition, the limited success of translating in vitro dissolution data into in vivo performance can be enhanced using innovative tools such as the in vitro dissolution and absorption systems (IDAS). By integrating in vitro dissolution and permeability tests, these systems can provide useful insights for formulation development. A thorough assessment of the potential of in vitro techniques, along with formalization of their use through regulatory science initiatives when appropriate, may lead to cost-effective tools to help address some of the quality and regulatory challenges faced in the Latin American and Caribbean region.

Case study 6. Transporter case studies: in vitro solutions for translatable outcomes

Assessing the interactions of a new drug candidate with transporters, either as a substrate or as an inhibitor, is no simple matter. There are many clinically relevant transporters, as many as nine to be evaluated for an FDA submission and up to eleven for the EMA as of 2013. Additionally, it is likely that if a compound is a substrate or inhibitor of one transporter, it will be so for other transporters as well. There are practically no specific substrates or inhibitors, presumably because the specificities of drug transporters are so broad and overlapping, and even fewer clinically relevant probes that can be used to evaluate transporter function in humans. In the case of some transporters, it is advisable to evaluate an NCE with more than one test system and/or more than one probe substrate in order to convince oneself (and regulatory authorities) that a clinical drug interaction study is not warranted. Finally, each test system has its own unique set of advantages and disadvantages. One has to really appreciate the nuances of the available tools (test systems, probe substrates, etc.) to select the best tools for the job and design the optimal in vitro experiment. In this chapter, several examples are used to illustrate the successful interpretation of in vitro data for both efflux and uptake transporters. Some data presented in this chapter is unpublished at the time of compilation of this book. It has been incorporated in this chapter to provide a sense of complexities in transporter kinetics to the reader.

Principles and experimental considerations for in vitro transporter interaction assays

Drug transporters are now universally acknowledged as important determinants of the absorption, distribution, metabolism and excretion of both endogenous and exogenous compounds. Altered transporter function, whether due to genetic polymorphism, DDIs, disease, or environmental factors such as dietary constituents, can result in changes in drug efficacy and/or toxicity due to changes in circulating or tissue levels of either drugs or endogenous substrates.Prediction of whether and to what extent the biological fate of a drug is influenced by drug transporters, therefore, requires in vitro test systems that can accurately predict the risk and magnitude of clinical DDIs. While these in vitro assessments appear simple in theory, practitioners recognize that there are multiple factors that can influence experimental outcomes. A better understanding of these variables, including test compound characteristics, test systems, assay formats, and experimental design will enable clear, actionable steps and translatable outcomes that may avoid unnecessary downstream clinical engagement. This chapter will delineate the role of these variables in improving in vitro assay outcomes.

A novel incubation direct injection LC/MS/MS technique for in vitro drug metabolism screening studies involving the CYP 2D6 and the CYP 3A4 isozymes

A direct injection LC/MS/MS method involving a novel incubation technique was developed for the inhibition screening of CYP 2D6 and CYP 3A4 isoenzymes using dextromethorphan and midazolam as probe substrates. Both assays were performed using an electrospray ionization source in the positive ion mode. Direct injection was possible by using a short C 18, LC column (2 mm x 20 mm) with large particle diameter packing (10 microm). Analytical characteristics of the direct injection technique were studied by examining matrix effects, which showed suppression of the ESI signal between 0.20 and 0.65 min. The retention times for analytes were adjusted to approximately 0.8 min (k'>3), resulting in no matrix effect. Column lifetime was evaluated and determined to be approximately 160 direct injections of the matrix. The precision and accuracy of the control samples for the quantitation of dextromethorphan was between -0.53 and -12.80, and 3.73 and 6.69% respectively. Unlike conventional incubation techniques, incubations were carried out in an autosampler equipped with a heating accessory. This novel incubation method, which involved no stirring of the incubation mixture, estimated the Cl(int in vitro) for dextromethorphan and midazolam in human liver microsomes to be 1.65+/-0.22 ml/(hmg) and 0.861 ml/(min mg) respectively. The autosampler tray maintained uniform temperature and was sensitive to changes in temperature between 33 and 41 degrees C. High-throughput screening was performed using known inhibitors of the CYP 2D6 isozyme, and the system was evaluated for its ability to differentiate between these inhibitors. The strong inhibitor quinidine resulted in a 25.6% increase in t(1/2), the medium potency inhibitor chlorpromazine resulted in an increase of 6.14% and the weak inhibitor primaquine had no significant effect on half-life. This technique involves no sample preparation, demonstrated run times of 2 min per injection and can be fully automated. The method should therefore prove to be a valuable tool in the drug discovery process.

Characterization of quinidine 3-hydroxylation as a probe for the CYP 3A enzyme using a novel capillary electrophoresis technique

Capillary electrophoresis (CE) with a direct injection technique was used to characterize the formation of (3S)-3-hydroxyquinidine (3-OHQ) as a probe for the CYP 3A isoenzymes in rat liver microsomes. Detection was performed either in the absorbance mode or by employing laser-induced fluorescence (LIF) detection. Michaelis-Menten parameters (mean values+/-S.D.) K(m) and V(max) for the formation of 3-OHQ from the probe drug quinidine sulfate (QS) in rat liver microsomes were 37+/-4.6 micro g/ml (47.1+/-5.9 micro M) and 321+/-4 ng/mg/h (942+/-11.7 pmol/mg/h), respectively. Inhibition studies were performed to evaluate the specificity of 3-OHQ as a probe for the CYP 3A enzyme. Ketoconazole and fluconazole were found to be inhibitors of 3-OHQ formation and exhibited K(i) values of 0.19 and 20.1 micro M, respectively. Inhibition with the weak inhibitor, erythromycin could only be estimated using LIF detection due to lack of sensitivity in the absorbance mode. The formation of 3-OHQ in rat liver microsomes can be used as a model for the screening of the CYP 3A enzyme. Direct injection, ensures faster analysis time due to the lack of sample preparation and the low volume capabilities of the technique makes it attractive for the screening of a large number of compounds.

Determination of (3S)-3-hydroxy quinidine for metabolism screening experiments using direct injection capillary electrophoresis and laser-induced fluorescence detection

Capillary electrophoresis (CE) has been used with collinear laser-induced fluorescence detection (LIF) to determine the amount of (3S)-3-hydroxy quinidine (3OHQ) formed on direct injection of microsomal incubation mixtures. 3OHQ is the CYP 3A4 metabolite of quinidine sulfate (QS) and is therefore useful for metabolism screening studies. The method was validated analytically and tested for its capability of screening for a weak inhibitor of the CYP 3A4 isozyme. A linear calibration was found to provide the best fit for the standard curve with a correlation of 0.9950 and all concentration residuals less than 15%. The percentage relative standard deviations (RSDs) of two controls, 175 and 2250 ng/mL, were 9.29 and 5.68% and the percentage differences from normal (DFN) were 6.87 and -4.37%, respectively. The concentration limit of detection (LOD) for 3OHQ in the incubation matrix was 52.11ng/mL and the mass LOD was approximately 521.1 fg (injection volume 10 nL). The effectiveness of the method to screen for the weak inhibitor erythromycin has been shown by calculating percentage inhibition when incubating with different concentrations of QS. Sensitive detection coupled with the convenience of the direct injection technique makes this an attractive approach for metabolism screening. The small sample size capability of CE will further reduce the quantities of probe drug, microsomes and other reagents required for incubation studies.

A direct injection capillary electrophoretic technique for miniaturized high-throughput metabolic screening of the CYP 3A4 enzyme using quinidine as a probe

A capillary electrophoresis (CE) method has been developed for the determination of quinidine sulfate (QS) and (3S)-3-hydroxyquinidine (3-OHQ) by direct injection of microsomal incubation mixtures. 3-OHQ is the CYP 3A4 metabolite of QS and hence useful for metabolism screening studies. The method was validated analytically and tested for its effectiveness as a metabolic inhibition model. A linear calibration was found to provide the best fit for the standard curve with an r of 0.9966 and all residuals less than 12%. The percent relative standard deviations (RSDs) of the two controls, 2 and 8 microg/ml were 5.27 and 2.90% and the percent difference from normal (% DFN) were -12.58 and -0.31% respectively. The limit of quantitation (LOQ) in the incubation matrix was 0.5 microg/ml. 3-OHQ formation complied with Michaelis-Menten kinetics and the mean values+/-S.D. of Km and Vmax were 36.98+/-4.62 microg/ml and 321.39+/-3.88 ng/mg/h respectively. Preliminary inhibition studies suggest that the method has adequate sensitivity to screen for high and medium inhibitors of the CYP 3A4 isozyme. The lack of sample preparation coupled with the small sample size capability of CE would enable the direct injection technique to aid in miniaturized high-throughput screening.