Assessing and mitigating pH-mediated DDI risks in drug development - formulation approaches and clinical considerations.

pH-mediated drug-drug interactions (DDI) is a prevalent DDI in drug development, especially for weak base compounds with highly pH-dependent solubility. FDA has released a guidance on the evaluation of pH-mediated DDI assessments using in vitro testing and clinical studies. Currently, there is no common practice of ways of testing across the academia and industry. The development of biopredictive method and physiologically-based biopharmaceutics modeling (PBBM) approaches to assess acid-reducing agent (ARA)-DDI have been proven with accurate prediction and could decrease drug development burden, inform clinical design and potentially waive clinical studies. Formulation strategies and careful clinical design could help mitigate the pH-mediated DDI to avoid more clinical studies and label restrictions, ultimately benefiting the patient. In this review paper, a detailed introduction on biorelevant dissolution testing, preclinical and clinical study requirement and PBPK modeling approaches to assess ARA-DDI are described. An improved decision tree for pH-mediated DDI is proposed. Potential mitigations including clinical or formulation strategies are discussed.

Physiologically Based Biopharmaceutics Modeling (PBBM): Best Practices for Drug Product Quality, Regulatory and Industry Perspectives: 2023 Workshop Summary Report.

Physiologically based biopharmaceutics modeling (PBBM) is used to elevate drug product quality by providing a more accurate and holistic understanding of how drugs interact with the human body. These models are based on the integration of physiological, pharmacological, and pharmaceutical data to simulate and predict drug behavior in vivo. Effective utilization of PBBM requires a consistent approach to model development, verification, validation, and application. Currently, only one country has a draft guidance document for PBBM, whereas other major regulatory authorities have had limited experience with the review of PBBM. To address this gap, industry submitted confidential PBBM case studies to be reviewed by the regulatory agencies; software companies committed to training. PBBM cases were independently and collaboratively discussed by regulators, and academic colleagues participated in some of the discussions. Successful bioequivalence "safe space" industry case examples are also presented. Overall, six regulatory agencies were involved in the case study exercises, including ANVISA, FDA, Health Canada, MHRA, PMDA, and EMA (experts from Belgium, Germany, Norway, Portugal, Spain, and Sweden), and we believe this is the first time such a collaboration has taken place. The outcomes were presented at this workshop, together with a participant survey on the utility and experience with PBBM submissions, to discuss the best scientific practices for developing, validating, and applying PBBMs. The PBBM case studies enabled industry to receive constructive feedback from global regulators and highlighted clear direction for future PBBM submissions for regulatory consideration.

Parameterization of Physiologically Based Biopharmaceutics Models: Workshop Summary Report.

This Article shares the proceedings from the August 29th, 2023 (day 1) workshop "Physiologically Based Biopharmaceutics Modeling (PBBM) Best Practices for Drug Product Quality: Regulatory and Industry Perspectives". The focus of the day was on model parametrization; regulatory authorities from Canada, the USA, Sweden, Belgium, and Norway presented their views on PBBM case studies submitted by industry members of the IQ consortium. The presentations shared key questions raised by regulators during the mock exercise, regarding the PBBM input parameters and their justification. These presentations also shed light on the regulatory assessment processes, content, and format requirements for future PBBM regulatory submissions. In addition, the day 1 breakout presentations and discussions gave the opportunity to share best practices around key questions faced by scientists when parametrizing PBBMs. Key questions included measurement and integration of drug substance solubility for crystalline vs amorphous drugs; impact of excipients on apparent drug solubility/supersaturation; modeling of acid-base reactions at the surface of the dissolving drug; choice of dissolution methods according to the formulation and drug properties with a view to predict the in vivo performance; mechanistic modeling of in vitro product dissolution data to predict in vivo dissolution for various patient populations/species; best practices for characterization of drug precipitation from simple or complex formulations and integration of the data in PBBM; incorporation of drug permeability into PBBM for various routes of uptake and prediction of permeability along the GI tract.

Physiologically Based Pharmacokinetics Modeling in Biopharmaceutics: Case Studies for Establishing the Bioequivalence Safe Space for Innovator and Generic Drugs.

For successful oral drug development, defining a bioequivalence (BE) safe space is critical for the identification of newer bioequivalent formulations or for setting of clinically relevant in vitro specifications to ensure drug product quality. By definition, the safe space delineates the dissolution profile boundaries or other drug product quality attributes, within which the drug product variants are anticipated to be bioequivalent. Defining a BE safe space with physiologically based biopharmaceutics model (PBBM) allows the establishment of mechanistic in vitro and in vivo relationships (IVIVR) to better understand absorption mechanism and critical bioavailability attributes (CBA). Detailed case studies on how to use PBBM to establish a BE safe space for both innovator and generic drugs are described. New case studies and literature examples demonstrate BE safe space applications such as how to set in vitro dissolution/particle size distribution (PSD) specifications, widen dissolution specification to supersede f2 tests, or application toward a scale-up and post-approval changes (SUPAC) biowaiver. A workflow for detailed PBBM set-up and common clinical study data requirements to establish the safe space and knowledge space are discussed. Approaches to model in vitro dissolution profiles i.e. the diffusion layer model (DLM), Takano and Johnson models or the fitted PSD and Weibull function are described with a decision tree. The conduct of parameter sensitivity analyses on kinetic dissolution parameters for safe space and virtual bioequivalence (VBE) modeling for innovator and generic drugs are shared. The necessity for biopredictive dissolution method development and challenges with PBBM development and acceptance criteria are described.

Current State and Opportunities with Long-acting Injectables: Industry Perspectives from the Innovation and Quality Consortium "Long-Acting Injectables" Working Group.

Long-acting injectable (LAI) formulations can provide several advantages over the more traditional oral formulation as drug product opportunities. LAI formulations can achieve sustained drug release for extended periods of time, which results in less frequent dosing requirements leading to higher patient adherence and more optimal therapeutic outcomes. This review article will provide an industry perspective on the development and associated challenges of long-acting injectable formulations. The LAIs described herein include polymer-based formulations, oil-based formulations, and crystalline drug suspensions. The review discusses manufacturing processes, including quality controls, considerations of the Active Pharmaceutical Ingredient (API), biopharmaceutical properties and clinical requirements pertaining to LAI technology selection, and characterization of LAIs through in vitro, in vivo and in silico approaches. Lastly, the article includes a discussion around the current lack of suitable compendial and biorelevant in vitro models for the evaluation of LAIs and its subsequent impact on LAI product development and approval.

Applications, Challenges, and Outlook for PBPK Modeling and Simulation: A Regulatory, Industrial and Academic Perspective.

Several regulatory guidances on the use of physiologically based pharmacokinetic (PBPK) analyses and physiologically based biopharmaceutics model(s) (PBBM(s)) have been issued. Workshops are routinely held, demonstrating substantial interest in applying these modeling approaches to address scientific questions in drug development. PBPK models and PBBMs have remarkably contributed to model-informed drug development (MIDD) such as anticipating clinical PK outcomes affected by extrinsic and intrinsic factors in general and specific populations. In this review, we proposed practical considerations for a "base" PBPK model construction and development, summarized current status, challenges including model validation and gaps in system models, and future perspectives in PBPK evaluation to assess a) drug metabolizing enzyme(s)- or drug transporter(s)- mediated drug-drug interactions b) dosing regimen prediction, sampling timepoint selection and dose validation in pediatric patients from newborns to adolescents, c) drug exposure in patients with renal and/or and hepatic organ impairment, d) maternal-fetal drug disposition during pregnancy, and e) pH-mediated drug-drug interactions in patients treated with proton pump inhibitors/acid-reducing agents (PPIs/ARAs) intended for gastric protection. Since PBPK can simulate outcomes in clinical studies with enrollment challenges or ethical issues, the impact of PBPK models on waivers and how to strengthen study waiver is discussed.

Translational Modeling Strategies for Orally Administered Drug Products: Academic, Industrial and Regulatory Perspectives.

During non-clinical and clinical development of a new molecular entity (NME), modeling and simulation (M&S) are routinely used to predict the exposure and pharmacokinetics (PK) of the drug compound in humans. The basic methodology and output are generally understood across all functional disciplines. However, this understanding is mostly restricted to traditional methods such as those in simplified kinetic models and void of adequate mechanistic foundation to address questions beyond the observed clinical data. In the past two decades, alternative and more mechanistic methods, particularly for describing absorption, distribution, excretion and metabolism (ADME) of drugs have been developed and applied under the general umbrella of physiologically-based pharmacokinetic (PBPK) methods. Their mechanistic nature gives the ability to ask many other questions which were not traditionally asked and provide some logically and evidenced-based potential answers. Whilst traditional PK methods are mainstream and understood by most scientists, mechanistic absorption models alongside other PBPK approaches are still deemed eclectic, despite making significant strides in the fundamental science as well as regulatory acceptance. On November 3rd, a short course was held at the annual American Association of Pharmaceutical Scientists (AAPS) meeting in San Antonio, Texas. The different talks were tailored to provide a basis or rationale for the subject, introduction to fundamental principles with historical perspective, a critique of the state-of-the-art, examples of successful application of the methods across different phases of the drug development process and the specific standards these mechanistic models should meet to be fully reliable from a regulatory perspective.

Verification of a physiologically based pharmacokinetic model of ritonavir to estimate drug-drug interaction potential of CYP3A4 substrates.

Ritonavir is one of several ketoconazole alternatives used to evaluate strong CYP3A4 inhibition potential in clinical drug-drug interaction (DDI) studies. In this study, four physiologically based pharmacokinetic (PBPK) models of ritonavir as an in vivo time-dependent inhibitor of CYP3A4 were created and verified for oral doses of 20, 50, 100 and 200 mg using the fraction absorbed (Fa ) and oral clearance (CLoral ) values reported in the literature, because transporter and CYP enzyme reaction phenotyping data were not available. The models were used subsequently to predict and compare the magnitude of the AUC increase in nine reference DDI studies evaluating the effect of ritonavir at steady-state on midazolam (CYP3A4 substrate) exposure. Midazolam AUC and Cmax ratios were predicted within 2-fold of the respective observations in seven studies. Simulations of the hepatic and gut CYP3A4 abundance after multiple oral dosing of ritonavir indicated that a 3-day treatment with ritonavir 100 mg twice daily is sufficient to reach maximal CYP3A4 inhibition and subsequent systemic exposure increase of a CYP3A4 substrate, resulting in the reliable estimation of fm,CYP3A4 . The ritonavir model was submitted as part of the new drug application for Kisqali® (ribociclib) and accepted by health authorities.

Midostaurin, a Novel Protein Kinase Inhibitor for the Treatment of Acute Myelogenous Leukemia: Insights from Human Absorption, Metabolism, and Excretion Studies of a BDDCS II Drug.

The absorption, metabolism, and excretion of midostaurin, a potent class III tyrosine protein kinase inhibitor for acute myelogenous leukemia, were evaluated in healthy subjects. A microemulsion formulation was chosen to optimize absorption. After a 50-mg [14C]midostaurin dose, oral absorption was high (>90%) and relatively rapid. In plasma, the major circulating components were midostaurin (22%), CGP52421 (32.7%), and CGP62221 (27.7%). Long plasma half-lives were observed for midostaurin (20.3 hours), CGP52421 (495 hours), and CGP62221 (33.4 hours). Through careful mass-balance study design, the recovery achieved was good (81.6%), despite the long radioactivity half-lives. Most of the radioactive dose was recovered in feces (77.6%) mainly as metabolites, because only 3.43% was unchanged, suggesting mainly hepatic metabolism. Renal elimination was minor (4%). Midostaurin metabolism pathways involved hydroxylation, O-demethylation, amide hydrolysis, and N-demethylation. High plasma CGP52421 and CGP62221 exposures in humans, along with relatively potent cell-based IC50 for FMS-like tyrosine kinase 3-internal tandem duplications inhibition, suggested that the antileukemic activity in AML patients may also be maintained by the metabolites. Very high plasma protein binding (>99%) required equilibrium gel filtration to identify differences between humans and animals. Because midostaurin, CGP52421, and CGP62221 are metabolized mainly by CYP3A4 and are inhibitors/inducers for CYP3A, potential drug-drug interactions with mainly CYP3A4 modulators/CYP3A substrates could be expected. Given its low aqueous solubility, high oral absorption and extensive metabolism (>90%), midostaurin is a Biopharmaceutics Classification System/Biopharmaceutics Drug Disposition Classification System (BDDCS) class II drug in human, consistent with rat BDDCS in vivo data showing high absorption (>90%) and extensive metabolism (>90%).

Integrated TK-TD modeling for drug-induced concurrent tachycardia and QT changes in beagle dogs.

Drug-induced cardiotoxicity, including tachycardia and QT prolongation, remains a major safety concern that needs to be identified and its risk mitigated in early stages of drug development. In the present study, an integrated toxicokinetic-toxicodynamic (TK-TD) modeling approach within a nonlinear mixed-effect modeling framework is applied to investigate concurrent abnormal heart rate and QT changes in three beagle dogs, using a Novartis internal compound (NVS001) as the case example. By accounting for saturable drug absorption, circadian rhythms, drug-effect tolerance, and nonlinear rate-dependency of QT interval, the dynamic TK-TD model captures the experimentally observed drug effects on heart rate and QT interval across a wide dosing range of NVS001 in beagle dogs. Further analyses reveal that the NVS001-induced QT prolongation observed in the low-dose groups is potentially caused by direct drug inhibition on the hERG channel, while the apparent QT shortening in the high-dose groups may be due to strong rate-dependency of QT at high heart rates. This study also suggests that the TK-TD model can be used to identify direct drug effects on the non-rate-dependent QT component by dissociating QT changes from tachycardia and deriving a new QT correction method. The integrated TK-TD model presented here may serve as a novel quantitative framework for evaluating drug-induced concurrent changes in heart rate and QT to potentially facilitate preclinical and clinical safety studies.

Antiviral Nucleotide Incorporation by Recombinant Human Mitochondrial RNA Polymerase Is Predictive of Increased In Vivo Mitochondrial Toxicity Risk.

Nucleoside or nucleotide inhibitors are a highly successful class of antivirals due to selectivity, potency, broad coverage, and high barrier to resistance. Nucleosides are the backbone of combination treatments for HIV, hepatitis B virus, and, since the FDA approval of sofosbuvir in 2013, also for hepatitis C virus (HCV). However, many promising nucleotide inhibitors have advanced to clinical trials only to be terminated due to unexpected toxicity. Here we describe the in vitro pharmacology of compound 1, a monophosphate prodrug of a 2'-ethynyluridine developed for the treatment of HCV. Compound 1 inhibits multiple HCV genotypes in vitro (50% effective concentration [EC50], 0.05 to 0.1 µM) with a selectivity index of >300 (50% cytotoxic concentration [CC50], 30 µM in MT-4 cells). The active triphosphate metabolite of compound 1, compound 2, does not inhibit human α, ß, or γ DNA polymerases but was a substrate for incorporation by the human mitochondrial RNA polymerase (POLRMT). In dog, the oral administration of compound 1 resulted in elevated serum liver enzymes and microscopic changes in the liver. Transmission electron microscopy showed significant mitochondrial swelling and lipid accumulation in hepatocytes. Gene expression analysis revealed dose-proportional gene signature changes linked to loss of hepatic function and increased mitochondrial dysfunction. The potential of in vivo toxicity through mitochondrial polymerase incorporation by nucleoside analogs has been previously shown. This study shows that even moderate levels of nucleotide analog incorporation by POLRMT increase the risk of in vivo mitochondrial dysfunction. Based on these results, further development of compound 1 as an anti-HCV compound was terminated.

Novel orally swallowable IntelliCap(®) device to quantify regional drug absorption in human GI tract using diltiazem as model drug.

Typically, colonic absorption of a drug is mandatory for a sustained release formulation to hold the drug's plasma level for more than 12 or 24 h above the minimum therapeutic plasma concentration (efficacy). According to Drugs@FDA, only 7.4% of the oral drugs are extended release forms probably showing colonic absorption. Therefore an early determination of a drug's colonic absorption using the IntelliCap® in animals or humans will provide the mandatory information to initiate or stop a SR form development. Diltiazem (60 mg) is used in the oral swallowable IntelliCap® and the marketed SR form from Mylan (coated beads). A human study with 14 healthy volunteers compared the Mylan formulation with the IntelliCap® device that releases the drug identical to the in-vitro dissolution of the Mylan product. The plasma profiles of IntelliCap® and Mylan formulation are highly similar. The mean AUC (bioequivalence fulfilled) and mean Cmax of IntelliCap® shows only a difference of +15% and -12%, respectively. But the PK profile of the Mylan formulation shows a broader peak around Cmax. About 81.8% diltiazem was absorbed in the colon (IntelliCap®) comparable to former publications. The Mylan is a SR diffusion coated beads form whereas the IntelliCap® is a monolithic capsule. The beads are transported in the gut and spread which results in a longer Tmax and a broader Cmax peak. The IntelliCap® device can quantitatively measure the colonic absorption of a drug in excellent accordance to a standard oral SR dosage form.

Application of physiologically based absorption modeling to formulation development of a low solubility, low permeability weak base: mechanistic investigation of food effect.

Physiologically based pharmacokinetic (PBPK) modeling has been broadly used to facilitate drug development, hereby we developed a PBPK model to systematically investigate the underlying mechanisms of the observed positive food effect of compound X (cpd X) and to strategically explore the feasible approaches to mitigate the food effect. Cpd X is a weak base with pH-dependent solubility; the compound displays significant and dose-dependent food effect in humans, leading to a nonadherence of drug administration. A GastroPlus Opt logD Model was selected for pharmacokinetic simulation under both fasted and fed conditions, where the biopharmaceutic parameters (e.g., solubility and permeability) for cpd X were determined in vitro, and human pharmacokinetic disposition properties were predicted from preclinical data and then optimized with clinical pharmacokinetic data. A parameter sensitivity analysis was performed to evaluate the effect of particle size on the cpd X absorption. A PBPK model was successfully developed for cpd X; its pharmacokinetic parameters (e.g., C max, AUCinf, and t max) predicted at different oral doses were within ±25% of the observed mean values. The in vivo solubility (in duodenum) and mean precipitation time under fed conditions were estimated to be 7.4- and 3.4-fold higher than those under fasted conditions, respectively. The PBPK modeling analysis provided a reasonable explanation for the underlying mechanism for the observed positive food effect of the cpd X in humans. Oral absorption of the cpd X can be increased by reducing the particle size (<100 nm) of an active pharmaceutical ingredient under fasted conditions and therefore, reduce the cpd X food effect correspondingly.

Physiologically Based Biopharmaceutics Modeling for Gefapixant IR Formulation Development and Defining the Bioequivalence Dissolution Safe Space.

Gefapixant is a weakly basic drug which has been formulated as an immediate release tablet for oral administration. A physiologically based biopharmaceutics model (PBBM) was developed based on gefapixant physicochemical properties and clinical pharmacokinetics to aid formulation selection, bioequivalence safe space assessment and dissolution specification settings. In vitro dissolution profiles of different free base and citrate salt formulations were used as an input to the model. The model was validated against the results of independent studies, which included a bioequivalence and a relative bioavailability study, as well as a human ADME study, all meeting acceptance criteria of prediction errors ≤ 20% for both Cmax and AUC.  PBBM was also applied to evaluate gastric pH-mediated drug-drug-interaction potential with co-administration of a proton pump inhibitor (PPI), omeprazole. Model results showed good agreement with clinical data in which omeprazole lowered gefapixant exposure for the free base formulation but did not significantly alter gefapixant pharmacokinetics for the citrate based commercial drug product. An extended virtual dissolution bioequivalence safe space was established.  Gefapixant drug product batches are anticipated to be bioequivalent with the clinical reference batch when their dissolution is > 80% in 60 minutes. PBBM established a wide dissolution bioequivalence space as part of assuring product quality.

Using Mechanistic Modeling Approaches to Support Bioequivalence Assessments for Oral Products.

This report summarizes the proceedings for Day 1 Session 3 of the 2-day public workshop entitled "Best Practices for Utilizing Modeling Approaches to Support Generic Product Development," a jointly sponsored workshop by the US Food and Drug Administration (FDA) and the Center for Research on Complex Generics (CRCG) in the year 2022. The aims of this workshop were to discuss how to modernize approaches for efficiently demonstrating bioequivalence (BE), to establish their role in modern paradigms of generic drug development, and to explore and develop best practices for the use of modeling and simulation approaches in regulatory submissions and approval. The theme of this session is mechanistic modeling approaches supporting BE assessments for oral drug products. As a summary, with more successful cases of PBPK absorption modeling being developed and shared, the general strategies/frameworks on using PBPK for oral products are being formed; this will help further evolvement of this area. In addition, the early communications between the industry and the agency through appropriate pathways (e.g., pre-abbreviated new drug applications (pre-ANDA) meetings) are encouraged, and this will speed up the successful development and utility of PBPK modeling for oral products.

Utility of physiologically based modeling and preclinical in vitro/in vivo data to mitigate positive food effect in a BCS class 2 compound.

Physiologically based pharmacokinetic (PBPK) modeling has become a useful tool to estimate the performance of orally administrated drugs. Here, we described multiple in silico/in vitro/in vivo tools to support formulation development toward mitigating the positive food effect of NVS123, a weak base with a pH-dependent and limited solubility. Administered orally with high-fat meal, NVS123 formulated as dry filled capsules displayed a positive food effects in humans. Three alternative formulations were developed and assessed in in vitro and in vivo preclinical and/or clinical studies. By integrating preclinical in vitro and in vivo data, the PBPK model successfully estimated the magnitude of food effects and the predicted values were within ± 30% of the observed results. A model-guided parameter sensitivity analysis illustrated that enhanced solubility and longer precipitation times under fed condition were the main reason for enhanced NVS123's exposure in presence of food. Eventually, exposure after an amorphous formulation was found to be not significantly altered because of remarkably enhanced intestinal solubility and reduced precipitation. Gastroplus population simulations also suggested that the amorphous formulation is promising in mitigating a clinically significant food effect. Overall, these efforts supported the rationale of clinical investigation of the new formulation, and more importantly, highlighted a practical application of PBPK modeling solving issues of undesirable food effects in weakly basic compounds based on preclinical in vitro/in vivo data.

Applications of Modeling and Simulation Approaches in Support of Drug Product Development of Oral Dosage Forms and Locally Acting Drug Products: a Symposium Summary.

The number of modeling and simulation applications, including physiologically based pharmacokinetic (PBPK) models, physiologically based biopharmaceutics modeling (PBBM), and empirical models, has been constantly increasing along with the regulatory acceptance of these methodologies. While aiming at minimizing unnecessary human testing, these methodologies are used today to support the development and approval of novel drug products and generics. Modeling approaches are leveraged today for assessing drug-drug interaction, informing dose adjustments in renally or hepatically impaired patients, perform dose selection in pediatrics and pregnant women and diseased populations, and conduct biopharmaceutics-related assessments such as establish clinically relevant specifications for drug products and achieve quality assurance throughout the product life cycle. In the generics space, PBPK analyses are utilized toward virtual bioequivalence assessments within the scope of alternative bioequivalence approaches, product-specific guidance development, and food effect assessments among others. Case studies highlighting the evolving and expanding role of modeling and simulation approaches within the biopharmaceutics space were presented at the symposium titled "Model Informed Drug Development (MIDD): Role in Dose Selection, Vulnerable Populations, and Biowaivers - Chemical Entities" and Prologue "PBPK/PBBM to inform the Bioequivalence Safe Space, Food Effects, and pH-mediated DDIs" at the American Association of Pharmaceutical Scientists (AAPS) PharmSci 360 Annual Meeting in Boston, MA, on October 16-19, 2022, and are summarized here.

Establishing the Safe Space via Physiologically Based Biopharmaceutics Modeling. Case Study: Fevipiprant/QAW039.

Physiologically based pharmacokinetic and absorption modeling has increasingly been implemented for biopharmaceutics applications to define the safe space for drug product quality attributes such as dissolution. For fevipiprant/QAW039, simulations were performed to assess the impact of in vitro dissolution on the in vivo performance of immediate-release film-coated tablets during development and scaling up to commercial scale. A fevipiprant dissolution safe space was established using observed clinical intravenous and oral PK data from bioequivalent and non-bioequivalent formulations. Quality control dissolution profiles with tablets were used as GastroPlus™ model inputs to estimate the in vivo dissolution in the gastrointestinal tract and to simulate human exposure. The model was used to evaluate the intraluminal performance of the dosage forms and to predict the absorption rate limits for the 450 mg dose. The predictive model performance was demonstrated for various oral dosage forms (150‒500 mg), including the non-bioequivalent batches in fasted healthy adults. To define the safe space at 450 mg, simulations were performed using theoretical dissolution profiles. A specification of Q = 80% dissolved in 60 min or less for an immediate-release oral solid dosage form reflected the boundaries of the safe space. The dissolution profile of the 450 mg commercial scale batch was within a dissolution region where bioequivalence is anticipated, not near an edge of failure for dissolution, providing additional confidence to the proposed acceptance criteria. Thus, the safe space allowed for a wider than 10% dissolution difference for bioequivalent batches, superseding f2 similarity analyses.

A Randomized, Double-Blind, Placebo-Controlled, Phase 1 Trial of Radiopaque Islatravir-Eluting Subdermal Implants for Pre-exposure Prophylaxis Against HIV-1 Infection.

BACKGROUND: Islatravir (MK-8591) is a deoxyadenosine analog in development for the treatment and prevention of HIV-1 infection. An islatravir-eluting implant could provide an additional option for pre-exposure prophylaxis (PrEP). SETTING: Previous data support a threshold islatravir triphosphate concentration for PrEP of 0.05 pmol/10 6 cells in peripheral blood mononuclear cells. Prototype islatravir-eluting implants were previously studied to establish general tolerability and pharmacokinetics (PKs) of islatravir relative to the threshold level. METHODS: In this randomized, double-blind, placebo-controlled, phase 1 trial, a next-generation radiopaque islatravir-eluting implant (48 mg, 52 mg, or 56 mg) or placebo implant was placed for a duration of 12 weeks in participants at low risk of HIV infection. Safety and tolerability, as well as PK for islatravir parent and islatravir triphosphate from plasma and peripheral blood mononuclear cells, were assessed throughout placement and 8 weeks after removal. RESULTS: In total, 36 participants (8 active and 4 placebo per dose arm) were enrolled and completed this study. Implants were generally well tolerated, with no discontinuations due to an adverse event, and no clear dose-dependence in implant-related adverse events. No clinically meaningful relationships were observed for changes in laboratory values, vital signs, or electrocardiogram assessments. Mean islatravir triphosphate levels at day 85 (0.101-0.561 pmol/10 6  cells) were above the PK threshold for all dose levels. CONCLUSION: Islatravir administered using a subdermal implant has the potential to be an effective and well-tolerated method for administering PrEP to individuals at risk of acquiring HIV-1.

Dissolution Profile Similarity Assessment-Best Practices, Decision Trees and Global Harmonization.

During the write-up of the meeting summary reports from the 2019 dissolution similarity workshop held at the University of Maryland's Center of Excellence in Regulatory Science and Innovation (M-CERSI), several coauthors continued their discussions to develop a "best-practice" document defining the steps required to assess dissolution profiles in support of certain biowaivers and postapproval changes. In previous reports, current challenges related to dissolution profile studies were discussed such that the steps outlined in the two flow charts ("decision trees") presented here can be applied. These decision trees include both recommendations for the use of equivalence procedures between reference and test products as well as application of the dissolution safe space concept. Common approaches towards establishing dissolution safe spaces are described. This paper encourages the preparation of protocols clearly describing why and how testing is performed along with the expected pass/fail criteria prior to generating data on the materials to be evaluated. The target audience of this manuscript includes CMC regulatory scientists, laboratory analysts, as well as statisticians from industry and regulatory health agencies involved in the assessment of product quality via in vitro dissolution testing. Building upon previous publications, this manuscript provides a solution to the current ambiguity related to dissolution profile comparison. The principles outlined in this and previous manuscripts provide a basis for global regulatory alignment in the application of dissolution profile assessment to support manufacturing changes and biowaiver requests.