Dose Selection Process Research Articles

Dose Optimization of Targeted Therapies for Oncologic Indications.

Therapeutic advances in oncology in the 21st century have contributed to significant declines in cancer mortality. Notably, targeted therapies comprised the largest proportion of oncology drugs approved by the United States (US) Food and Drug Administration (FDA) over the past 25 years and have become the standard of care for the treatment of many cancers. However, despite the metamorphosis of the therapeutic landscape, some aspects of cancer drug development have remained essentially unchanged. In particular, the dose-finding methodology originally developed for cytotoxic chemotherapy drugs continues to be implemented, even though this approach no longer represents the most appropriate strategy for modern cancer therapies. In recognition of the need to reconsider assumptions, adapt the dose selection process for newer drugs, and design alternative strategies, the FDA has undertaken several initiatives in recent years to address these concerns. These actions include the launch of Project Optimus in 2021 and the issuance of draft guidance for industry on dose optimization of oncology drugs in 2023. Amid this evolving regulatory environment, the present manuscript reviews case studies for six different targeted cancer therapies, highlighting how dose-finding challenges have been managed to date by oncologists, sponsors, and regulators.

Abstract 2115: Assessing BCL2 protein complex level in peripheral blood mononuclear cells as a surrogate pharmacodynamic biomarker of BCL2 inhibitors in hematological cancers

Abstract In the last decade, cancer therapeutics have adhered to the practice of administering drugs at the maximum tolerated dose (MTD) selected from limited patient cohorts. The emergence of targeted therapies has disrupted this dose selection paradigm, as optimal efficacy may be achievable at lower dose than MTD. Recently, a regulatory agency initiated "OPTIMUS" to redefine the dose selection process, recommending quantitative assessments of drug efficacy in relation to the target protein throughout development and clinical trials. ABT-199 is a protein interaction inhibitor that specifically disrupts the interaction of BCL2 protein. Consequently, the assessment of changes in the level of BCL2 protein complex is necessary to evaluate the ABT-199 efficacy for optimal dose selection. In this study, we adapted the Single-molecule Protein Interaction Detection platform for evaluating pharmacodynamics of BCL2 inhibitors in clinical samples. We assessed the dissociation of two BCL2-related biomarkers, BCL2-BAX and BCL2-BIM, from a model system under various ABT-199 doses. Following one hour treatment with 300 nM of ABT-199, the BCL2-BAX complex dissociated almost by 40%, while 80% of the BCL2-BIM complex remained. The reduction of the BCL2-BIM complex was not changed when extending the treatment for 3 hours, indicating that the BCL2-BAX complex may serve as a more sensitive biomarker for assessing the target engagement of ABT-199. To determine the assay sensitivity, we evaluated the ABT-199 response across different cell numbers and found that 100,000 cells are sufficient for performing the BCL2-BAX assay. Subsequently, we validated the utility of our method in assessing clinical samples, specifically BMMCs and PBMCs. We collected 4 PBMCs and the corresponding BMMCs from hematological cancer patients and treated them with various doses of ABT-199 ex vivo. With 100,000 BMMCs and 1,000,000 PBMCs, we can generate dose-response curves for the BCL2-BAX complex at doses of ABT-199 ranging from 1 to 1,000 nM. To explore the feasibility of employing the BCL2-BAX complex in PBMCs as a surrogate biomarker for assessing ABT-199 engagement with BCL2 in BMMCs, we compared the averaged dose-response curves from 4 PBMCs with that of BMMCs. Remarkably, the two curves showed a coherent dissociation trend, indicating that the biochemical effect of ABT-199 on the BCL2-BAX complex may be conserved across different sample types. Collectively, we have developed a target engagement assay for BCL2 inhibitors by measuring the BCL2-BAX complex. Notably, we observed a consistent dissociation pattern of the BCL2-BAX complex by ABT-199 treatment in both PBMCs and BMMCs. This molecular information offers an alternative way to assess the pharmacodynamics of BCL2 inhibitors, particularly in the case where collecting a series of BMMCs with sufficient amounts may not be feasible. Citation Format: Hongwon Lee, Byungsan Choi, Saem Hong, Yunseo Lee, Tae-Young Yoon, Janghee Woo. Assessing BCL2 protein complex level in peripheral blood mononuclear cells as a surrogate pharmacodynamic biomarker of BCL2 inhibitors in hematological cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2115.

Pharmacokinetic / Pharmacodynamic (PK/PD) Simulations Guide Selection of the Dose for Administration of Efgartigimod Subcutaneously in a Phase 3 Clinical Trial in Patients with Primary Immune Thrombocytopenia

IntroductionEfgartigimod (ARGX-113) is a human IgG1-derived Fc fragment that binds with high affinity to FcRn in a pH dependent way, resulting in a blockade of FcRn-mediated recycling of IgGs. This leads to rapid degradation of all IgGs, including disease associated autoantibodies.The efficacy, safety, tolerability, and pharmacokinetic (PK) and pharmacodynamic (PD) profile of intravenously (IV) administered efgartigimod have been assessed during a Phase 1 study in healthy subjects (Ulrichts P. JCI. 2018;128), Phase 2 studies in patients with Myasthenia gravis (MG) (Howard JF. Neurol. 2019;92) and Immune Thrombocytopenia (ITP) (Newland AC. Am J Hematol. 2020;95:178-187), and a Phase 3 study in MG (Howard JF. Lancet Neurol. 2021;20). These studies have demonstrated that a dose of 10 mg/kg efgartigimod, administered in four weekly (qw) IV infusions, achieves close to maximal immunoglobulin G (IgG) reduction and a significant reduction of pathogenic autoantibodies in patients with ITP and MG. Furthermore, this dose was well-tolerated in all populations. Based on the results of the Phase 2 study in Primary ITP, a Phase 3 study was designed for IV administration in patients with persistent or chronic primary ITP (ADVANCE NCT04188379).To allow for a convenient SC administration of efgartigimod at a dose that achieves a similar PD effect comparable to IV 10 mg/kg, a co-formulation with rHuPH20 SC was developed (recombinant human hyaluronidase PH20, an enzyme used to increase the dispersion and absorption of co-administered substances when administered subcutaneously). Here we describe the dose selection process for the SC dose to be used in a Phase 3 study of patients with persistent or chronic ITP.MethodsPK and PD data from a Phase 1 study, including 32 healthy adult male subjects receiving 750 mg, 1250 mg, 1750 mg, or 10 mg/kg single SC injections of efgartigimod co-mixed with rHuPH20 (8 subjects/dose group), were used for a PK/PD analysis to predict the efgartigimod PH20 SC dose that would result in a similar PD effect compared to the benchmark dose from previous studies of 10 mg/kg IV (1 hour infusion and body weight of 70 kg).ResultsWeekly SC administration of 1000 mg efgartigimod co-mixed with 2000 U/mL rHuPH20 was predicted to result in comparable maximum total IgG reduction after the 4 th SC injection (days 22-29) as after the 4 th IV infusion of 10 mg/kg administered qw (Figure 1). Additionally, the area under the curve for total IgG concentration after the 4th dose (days 22-29) and trough IgG reduction (measured prior to dose on day 29) were predicted to be comparable between weekly 1000 mg SC and the weekly 10 mg/kg IV benchmark dose.No statistically significant effect of body weight on the PK and PD of efgartigimod PH20 SC was found.DiscussionThese results informed the weekly SC dose administration schedule in ADVANCE SC, a Phase 3, multicenter, randomized, double-blinded, placebo-controlled trial (NCT04687072) for evaluation of efficacy and safety of efgartigimod PH20 SC in adults with persistent or chronic primary ITP. Efgartigimod PH20 SC or placebo PH20 SC will be given weekly on visits 1-4 and then either weekly or every other week from visits 5 to 16, as determined by platelet counts. The frequency of administration will remain unchanged for the last 7 weeks (visits 17 to 24) to evaluate the sustainable platelet count improvement as the primary objective. Secondary objectives include extent of disease control (overall platelet count response, use of rescue treatment, and changes in concurrent ITP therapy), bleeding events, and quality of life assessments. ADVANCE SC recruitment is currently ongoing across approximately 70 sites in Asia-Pacific, Europe, Japan, Latin America, Middle East, Africa, and USA. [Display omitted] DisclosuresGhanima: Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Principia: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Bayer: Honoraria, Research Funding; Pfizer: Research Funding. McDonald: Bayer, Sobi, Novartis, Amgen, argenx: Honoraria; Grifols: Research Funding. Jain: GBT: Speakers Bureau; Novartis: Speakers Bureau; Argenx: Other: advisory board; Sanofi: Other: advisory board; DOVA: Other: advisory board. Oliva: Novartis, Celgene, Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Daiichi: Consultancy; Alexion, argenx, Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Hultberg: argenx: Current Employment, Patents & Royalties. Gandini: argenx: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. Hofman: argenx: Current Employment. Van Bragt: Curare Consulting BV: Other: Partner; argenx: Consultancy. Parys: argenx: Current Employment. van Hoorick: argenx: Current Employment. Miyakawa: Sanofi: Consultancy; Zenyaku Kogyo: Consultancy; Sanofi: Research Funding; argenx: Consultancy, Research Funding. Broome: Alexion, argenx, Apellis, Sanofi: Honoraria.

Opportunities and challenges related to saturation of toxicokinetic processes: Implications for risk assessment

Top dose selection for repeated dose animal studies has generally focused on identification of apical endpoints, use of the limit dose, or determination of a maximum tolerated dose (MTD). The intent is to optimize the ability of toxicity tests performed in a small number of animals to detect effects for hazard identification. An alternative approach, the kinetically derived maximum dose (KMD), has been proposed as a mechanism to integrate toxicokinetic (TK) data into the dose selection process. The approach refers to the dose above which the systemic exposures depart from being proportional to external doses. This non-linear external-internal dose relationship arises from saturation or limitation of TK process(es), such as absorption or metabolism. The importance of TK information is widely acknowledged when assessing human health risks arising from exposures to environmental chemicals, as TK determines the amount of chemical at potential sites of toxicological responses. However, there have been differing opinions and interpretations within the scientific and regulatory communities related to the validity and application of the KMD concept. A multi-stakeholder working group, led by the Health and Environmental Sciences Institute (HESI), was formed to provide an opportunity for impacted stakeholders to address commonly raised scientific and technical issues related to this topic and, more specifically, a weight of evidence approach is recommended to inform design and dose selection for repeated dose animal studies. Commonly raised challenges related to the use of TK data for dose selection are discussed, recommendations are provided, and illustrative case examples are provided to address these challenges or refute misconceptions.

Optimal dose selection in oncology biologics development: Need for a paradigm shift.

3093 Background: In oncology, the recommended phase 2 dose (RP2D) is typically selected from the first-in-patient (FIP) dose escalation and then carried forward to late stage trials. The RP2D is often informed by limited data from a relatively small number of patients. Further dose optimization in late stage trials is rare as these trials often evaluate only one dose/dosing regimen. Traditionally oncology development relied on establishing an MTD with the expectation this dose would ultimately provide an optimal benefit/risk profile. However, for biologics there are clear examples suggesting a need to reconsider this approach to dose selection during drug development. The present review attempts to evaluate the dose selection approaches for approved oncology biologics to identify opportunities for improved dose optimization of future oncology drugs. Methods: The dose selection steps for oncology biologics approved by the USFDA from 2010 to 2020 were reviewed. The primary focus of the review was RP2D selection based on early clinical data, doses tested in pivotal trials, exposure-response and dose justification for the proposed dose, and post-marketing requirements (PMR) or post-marketing commitments (PMC) related to dose optimization. Results: The dose selection process for a total of 22 biologics was analyzed. Among these, 17 (77%) did not identify MTD during the FIP trial, and 6 (27%) tested more than one dose in the registration trials. In the initial approval, 2 (10%) had PMR or PMC for further dose optimization. For majority of the biologics the dose justification was based on 1) receptor occupancy 2) biomarker response 3) early clinical activity and 4) target efficacious concentration based on xenograft data. The majority of biologics had shown a shallow exposure-response relationship in safety or efficacy end points which partly can be attributed to the common practice of testing single dose level in the registrational trial. The dose recommended in the FDA label appears to be highly correlated to the RP2D determined in FIP studies. Conclusions: Oncology biologics have heavily relied on pharmacodynamic, early signs of efficacy, and safety data from the limited number of patients in the FIP dose escalation to identify the dose for pivotal trials. In most cases, there have been no dose ranging or optimization based on the final therapeutic outcome. While integration of relevant biomarker, PK, and PD data for optimal dose selection is an important aspect, there is a need to change the paradigm to consider more robust dose optimization, especially in early stage development. Dose ranging assessments incorporating therapeutically relevant endpoints and adequate sample size should be considered, ideally prior to pivotal trials.

A Review of the Dose Justification of Phase 3 Trials to Regulatory Authorities for Drugs Intended for the Treatment of Type 2 Diabetes in Europe.

Aims: Cardiovascular outcome trials with anti-diabetic drugs suggest that additional cardiovascular benefit can be achieved independent of improving glycaemic control. Nonetheless, dose selection of anti-diabetic drugs is typically based solely on glycaemic effects. We evaluated whether off-target drug effects are currently considered for dose justification to regulatory agencies. Methods: In the European Union, anti-diabetic drugs are registered by the European Medicines Agency. We extracted available information regarding dose selection from public assessment reports and marketing application dossiers. Descriptive statistics were used to summarise the extracted information. Results: In total, 14 drugs of three drug classes were included; sodium-glucose co-transporter-2 inhibitors (n = 4), dipeptidyl peptidase-4 inhibitors (n = 4) and glucagon-like peptide-1 receptor agonists (n = 6). For these drugs, 21 dose-finding trials were submitted including results of multiple off-target effects, of which body weight (n = 18) and low-density lipoprotein cholesterol (n = 14) were most frequently reported. Dose-response curves for off-target effects appeared to be different compared to the glycaemic dose-response curve. Glycated hemoglobin (100%) and fasting plasma glucose (42.9%), were used most frequently for the dose justification, but generally off-target effects (<25%) were not. Conclusions: Dose justification to regulatory authorities was mainly based on glycaemic effects. The dose-response relationship for the off-target effects did not necessarily follow the dose-response relationship of the on-target effects suggesting that selection of the optimal anti-diabetic dose could benefit from including off-target effects in the dose selection process as well.

Utility-Based Dose Selection for Phase II Dose-Finding Studies.

Dose selection is a key feature of clinical development. Poor dose selection has been recognized as a major driver of development failure in late phase. It usually involves both efficacy and safety criteria. The objective of this paper is to develop and implement a novel fully Bayesian statistical framework to optimize the dose selection process by maximizing the expected utility in phase III. The success probability is characterized by means of a utility function with two components, one for efficacy and one for safety. Each component refers to a dose-response model. Moreover, a sequential design (with futility and efficacy rules at the interim analysis) is compared to a fixed design in order to allow one to hasten the decision to perform the late phase study. Operating characteristics of this approach are extensively assessed by simulations under a wide range of dose-response scenarios. Simulation results illustrate the difficulty of simultaneously estimating two complex dose-response models with enough accuracy to properly rank doses using an utility function combining the two. The probability of making the good decision increases with the sample size. For some scenarios, the sequential design has good properties: with a quite large probability of study termination at interim analysis, it enables to reduce the sample size while maintaining the properties of the fixed design.

A Personalized Medicine Approach Using Clinical Utility Index and Exposure-Response Modeling Informed by Patient Preferences Data.

Selection of a personalized dose for an individual patient can be informed by the patient’s preferences, translated as weights on each of the clinically relevant safety and efficacy drug attributes, based on results from a brief patient preference elicitation questionnaire. In this analysis, the weighted attributes were simulated to represent various endometriosis patient profiles. Exposure‐response simulations were performed for elagolix, a drug approved for management of moderate to severe pain associated with endometriosis, across a range of plasma exposures corresponding to a range of doses. The results were combined to calculate a personalized clinical utility index. An interactive user‐friendly online application was developed and envisioned as a physician’s desk tool to personalize the dose selection process based on individual patient preferences. This demonstration should serve as an example of how patient/physician conversation can be facilitated with quantitative tools for personalizing the dose.

Bayesian optimization design for dose-finding based on toxicity and efficacy outcomes in phase I/II clinical trials.

In phase I trials, the main goal is to identify a maximum tolerated dose under an assumption of monotonicity in dose-response relationships. On the other hand, such monotonicity is no longer applied to biologic agents because a different mode of action from that of cytotoxic agents potentially draws unimodal or flat dose-efficacy curves. Therefore, biologic agents require an optimal dose that provides a sufficient efficacy rate under an acceptable toxicity rate instead of a maximum tolerated dose. Many trials incorporate both toxicity and efficacy data, and drugs with a variety of modes of actions are increasingly being developed; thus, optimal dose estimation designs have been receiving increased attention. Although numerous authors have introduced parametric model-based designs, it is not always appropriate to apply strong assumptions in dose-response relationships. We propose a new design based on a Bayesian optimization framework for identifying optimal doses for biologic agents in phase I/II trials. Our proposed design models dose-response relationships via nonparametric models utilizing a Gaussian process prior, and the uncertainty of estimates is considered in the dose selection process. We compared the operating characteristics of our proposed design against those of three other designs through simulation studies. These include an expansion of Bayesian optimal interval design, the parametric model-based EffTox design, and the isotonic design. In simulations, our proposed design performed well and provided results that were more stable than those from the other designs, in terms of the accuracy of optimal dose estimations and the percentage of correct recommendations.

Tailoring early-phase clinical trial design to address multiple research objectives.

In contemporary oncology drug development, implementation of novel early-phase designs with the ability to address multiple research objectives is needed to better refine regimens. This paper describes an adaptive design strategy for identifying a range of optimal regimens based on two endpoints within multiple cohorts. The proposed design was developed to address objectives in an early-phase trial of cancer vaccines in combination with agonistic antibodies to CD40 and CD27. We describe a model-based design strategy that was developed for a trial evaluating the safety and immunogenicity of vaccination with (1) peptides plus CD40 antibody and TLR3 ligand, (2) systemic administration of an agonistic CD27 antibody, and (3) to assess immune response from (1) and (2) compared to optimal controls in participants with stage IIB-IV melanoma. The proposed design is a practical adaptive method for use with combined immunotherapy regimens with multiple objectives within multiple cohorts of interest. Further advances in the effectiveness of cancer immunotherapies will require new approaches that include redefining optimal strategies to take multiple regimens forward into later phases, incorporating additional endpoints in the dose selection process and testing drug combination therapies to improve efficacy and reduce toxicity. Our goal is to facilitate the acceptance and application of more novel designs in contemporary early development trials.

Dose Selection Process for Younger Children Participating in a Phase 3 Study to Evaluate the Efficacy and Safety of Rivipansel (GMI-1070) in the Treatment of Vaso-Occlusive Crisis in Hospitalized Patients with Sickle Cell Disease

Background: Rivipansel is a pan-selectin inhibitor in development for the treatment of sickle cell disease (SCD) vaso-occlusive crisis (VOC). A single phase 3 study was planned to evaluate the efficacy and safety of rivipansel (GMI-1070) in the treatment of VOC in hospitalized patients with SCD. Selection of the dose to be used in this phase 3 study was based on the efficacy, safety, and pharmacokinetic (PK) results from the rivipansel phase 2 study. Modeling and Simulation (M&S) was used to determine the dosing for adults and children aged >6 years with SCD. To ensure that the predicted drug exposure is actually achieved in patients aged 6-11 years (cohort 2), we conducted a blinded review of the PK data obtained from several subjects enrolled in cohort 2. The methodology for this evaluation is presented here.Methods: Pharmacokinetic data for 109 subjects receiving doses of 2 to 40 mg/kg in 4 previous studies (3 Phase 1 and 1 Phase 2) were integrated to build a 3-compartment model, which was used to perform simulations to aid dose selection. As rivipansel is almost entirely renally excreted, the simulations of clearance considered renal function as well as hyperfiltration, as this type of altered renal filtration is common in SCD patients. This model allowed for scaling of the PK exposure from the model developed in adults and older children (aged 12-17 years) (Tammara BK, Harnisch LO. CPT Pharmacometrics Syst Pharmacol 2017;6:845-54) into the model for younger children (aged 6-11 years). Simulations from the model in the adult and pediatric population are presented in Figure 1.To confirm the predicted exposure in cohort 2, in particular their average concentration at steady-state (Cavg,ss), age- and weight-dependent cumulative distribution functions (CDFs) of parameters in the population PK model (eg, CL Vss) were derived for the first 6 actively treated children. During this blinded review, concentration time profiles for these children were generated and empirical Bayesian estimates (EBEs) for their corresponding Cavg,ss were derived. The percentiles in which the EBEs fell within the simulated CDFs from the model were used to guide decisions for a potential dose adjustment. This process is outlined in the flow chart in Figure 2 and in the percentile plot diagram shown in Figure 3.Results: The PK data from the Phase 2 study supported fixed flat dosing for patient aged 12 years and older. Pharmacokinetic M&S predicted that a loading dose of 1680 mg followed by a maintenance dose of 840 mg every 12 hours would result in exposures similar to those observed with the lower dose used in the Phase 2 study, such that a minimum plasma concentration >10 μg/mL would be maintained throughout the dosing interval. For patients in cohort 2, weight-based dosing was considered, as it is the most conservative approach, given that children in this age range have not been studied previously. For each dosing regimen tested, the simulated demographic target distribution in pediatric SCD patients was used to derive concentration-time profiles. A summary of the Cavg,ss distribution across different ages is shown in Figure 1. The simulations showed that for children aged 6-11 years, a 40-mg/kg loading dose (maximum 1680 mg) followed by 20 mg/kg every 12 hours (maximum 840 mg) would likely result in concentrations similar to those observed with the 20/10 mg/kg dosing used in adults in the Phase 2 study. To confirm the validity of the exposure predictions, PK assessments were performed in the Phase 3 study and a blinded interim analysis of pediatric exposures was conducted.Conclusions: A population PK model for rivipansel has been developed, applicable to the whole target SCD population of adults and children older than 12 years. Its applicability in children aged 6-11 years is under investigation as part of the ongoing Phase 3 study, and interim assessments of the PK exposure have been done in small cohorts of 6 patients. The corresponding decision framework has been implemented, exercised successfully, with the results of potential dose adaptations to be published once the Phase 3 study has been concluded. [Display omitted] DisclosuresTammara:Pfizer Inc.: Employment. Shafer:Pfizer Inc.: Employment. Harnisch:Pfizer Inc.: Employment.

Design considerations for early-phase clinical trials of immune-oncology agents

BackgroundWith numerous and fast approvals of different agents including immune checkpoint inhibitors, monoclonal antibodies, or chimeric antigen receptor (CAR) T-cell therapy, immunotherapy is now an established form of cancer treatment. These agents have demonstrated impressive clinical activity across many tumor types, but also revealed different toxicity profiles and mechanisms of action. The classic assumptions imposed by cytotoxic agents may no longer be applicable, requiring new strategies for dose selection and trial design.DescriptionThis main goal of this article is to summarize and highlight main challenges of early-phase study design of immunotherapies from a statistical perspective. We compared the underlying toxicity and efficacy assumptions of cytotoxic versus immune-oncology agents, proposed novel endpoints to be included in the dose-selection process, and reviewed design considerations to be considered for early-phase trials. When available, references to software and/or web-based applications were also provided to ease the implementation. Throughout the paper, concrete examples from completed (pembrolizumab, nivolumab) or ongoing trials were used to motivate the main ideas including recommendation of alternative designs.ConclusionFurther advances in the effectiveness of cancer immunotherapies will require new approaches that include redefining the optimal dose to be carried forward in later phases, incorporating additional endpoints in the dose selection process (PK, PD, immune-based biomarkers), developing personalized biomarker profiles, or testing drug combination therapies to improve efficacy and reduce toxicity.

Model selection and averaging of nonlinear mixed-effect models for robust phase III dose selection

Population model-based (pharmacometric) approaches are widely used for the analyses of phase IIb clinical trial data to increase the accuracy of the dose selection for phase III clinical trials. On the other hand, if the analysis is based on one selected model, model selection bias can potentially spoil the accuracy of the dose selection process. In this paper, four methods that assume a number of pre-defined model structure candidates, for example a set of dose–response shape functions, and then combine or select those candidate models are introduced. The key hypothesis is that by combining both model structure uncertainty and model parameter uncertainty using these methodologies, we can make a more robust model based dose selection decision at the end of a phase IIb clinical trial. These methods are investigated using realistic simulation studies based on the study protocol of an actual phase IIb trial for an oral asthma drug candidate (AZD1981). Based on the simulation study, it is demonstrated that a bootstrap model selection method properly avoids model selection bias and in most cases increases the accuracy of the end of phase IIb decision. Thus, we recommend using this bootstrap model selection method when conducting population model-based decision-making at the end of phase IIb clinical trials.

Tg.rasH2 Mice and not CByB6F1 Mice Should Be Used for 28-Day Dose Range Finding Studies Prior to 26-Week Tg.rasH2 Carcinogenicity Studies.

Our recent retrospective analysis of data, collected from 29 Tg.rasH2 mouse carcinogenicity studies, determined how successful the strategy of choosing the high dose for the 26-week studies was based on the estimated maximum tolerated dose (EMTD) derived from earlier 28-day dose range finding (DRF) studies conducted in CByB6F1 mice. Our analysis demonstrated that the high doses applied at EMTD in the 26-week Tg.rasH2 studies failed to detect carcinogenic effects. To investigate why the dose selection process failed in the 26-week carcinogenicity studies, the initial body weights, terminal body weights, body weight gains, food consumption, and mortality from the first 4 weeks of 26-week studies with Tg.rasH2 mice were compared with 28-day DRF studies conducted with CByB6F1 mice. Both the 26-week and the earlier respective 28-day studies were conducted with the exact same vehicle, test article, and similar dose levels. The analysis of our results further emphasizes that the EMTD and subsequent lower doses, determined on the basis of the 28-day studies in CByB6F1 mice, may not be an accurate strategy for selecting appropriate dose levels for the 26-week carcinogenicity studies in Tg.rasH2 mice. Based on the analysis presented in this article, we propose that the Tg.rasH2 mice and not the CByB6F1 mice should be used in future DRF studies. The Tg.rasH2 mice demonstrate more toxicity than the CByB6F1 mice, possibly because of their smaller size compared to CByB6F1 mice. Also, the Tg.rasH2 males appear to be more sensitive than the female Tg.rasH2 mice.

The effect of dose on the safety and immunogenicity of the VSV Ebola candidate vaccine: a randomised double-blind, placebo-controlled phase 1/2 trial

Safe and effective vaccines against Ebola could prevent or control outbreaks. The safe use of replication-competent vaccines requires a careful dose-selection process. We report the first safety and immunogenicity results in volunteers receiving 3 × 10(5) plaque-forming units (pfu) of the recombinant vesicular stomatitis virus-based candidate vaccine expressing the Zaire Ebola virus glycoprotein (rVSV-ZEBOV; low-dose vaccinees) compared with 59 volunteers who had received 1 ×10(7) pfu (n=35) or 5 × 10(7) pfu (n=16) of rVSV-ZEBOV (high-dose vaccinees) or placebo (n=8) before a safety-driven study hold. The Geneva rVSV-ZEBOV study, an investigator-initiated phase 1/2, dose-finding, placebo-controlled, double-blind trial conducted at the University Hospitals of Geneva, Switzerland, enrolled non-pregnant, immunocompetent, and otherwise healthy adults aged 18-65 years. Participants from the low-dose group with no plans to deploy to Ebola-aff5cted regions (non-deployable) were randomised 9:1 in a double-blind fashion using randomly permuted blocks of varying sizes to a single injection of 3 × 10(5) pfu or placebo, whereas deployable participants received single-injection 3 × 10(5) pfu open-label. Primary safety and immunogenicity outcomes were the incidence of adverse events within 14 days of vaccination and day-28 antibody titres, respectively, analysed by intention to treat. After viral oligoarthritis was observed in 11 of the first 51 vaccinees (22%) receiving 10(7) or 5 × 10(7) pfu, 56 participants were given a lower dose (3 × 10(5) pfu, n=51) or placebo (n=5) to assess the effect of dose reduction on safety and immunogenicity. This trial is ongoing with a follow-up period of 12 months; all reported results are from interim databases. This study is registered with ClinicalTrials.gov, number NCT02287480. Between Jan 5 and Jan 26, 2015, 43 non-deployable participants received low-dose rVSV-ZEBOV (3 × 10(5) pfu) or placebo in a double-blind fashion, whereas 13 deployable participants received 3 × 10(5) pfu open-label. Altogether, in the low-dose group, 51 participants received rVSV-ZEBOV and five received placebo. No serious adverse events occurred. At 3 × 10(5) pfu, early-onset reactogenicity remained frequent (45 [88%] of 51 compared with 50 [98%] of 51 high dose and two [15%] of 13 placebo recipients), but mild. Objective fever was present in one (2%) of 51 low-dose versus 13 (25%) of 51 high-dose vaccinees receiving at least 1 ×10(7) pfu (p<0·0001). Subjective fever (p<0·0001), myalgia (p=0·036), and chills (p=0·026) were significantly reduced and their time of onset delayed, reflecting significantly lower viraemia (p<0·0001) and blood monocyte-activation patterns (p=0·0233). Although seropositivity rates remained similarly high (48 [94%] of 51), day-28 EBOV-glycoprotein-binding and neutralising antibody titres were lower in low-dose versus high-dose vaccinees (geometric mean titres 344·5 [95% CI 229·7-516·4] vs 1064·2 [757·6-1495·1]; p<0·0001; and 35·1 [24·7-50·7] vs 127·0 [86·0-187·6]; p<0·0001, respectively). Furthermore, oligoarthritis again occurred on day 10 (median; IQR 9-14) in 13 (25%) of 51 low-dose vaccinees, with maculopapular, vesicular dermatitis, or both in seven (54%) of 13; arthritis was associated with increasing age in low-dose but not high-dose vaccinees. Two vaccinees presented with purpura of the lower legs; histological findings indicated cutaneous vasculitis. The presence of rVSV in synovial fluid and skin lesions confirmed causality. Reducing the dose of rVSV-ZEBOV improved its early tolerability but lowered antibody responses and did not prevent vaccine-induced arthritis, dermatitis, or vasculitis. Like its efficacy, the safety of rVSV-ZEBOV requires further definition in the target populations of Africa. Wellcome Trust through WHO.

Designing first‐in‐human dose of coagulation factors: application of pharmacokinetic allometric scaling

The objectives of this study were to (i) evaluate the predictive performance of pharmacokinetic interspecies scaling of coagulation factors to predict clearance (CL) and (ii) project first-in-human dose based on the predicted human CL. Human CL of nine coagulation factors was predicted using two or three animal species using two methods: (i) CL vs. body weight (simple allometry) and where applicable (ii) the product of CL and brain weight vs. body weight. Based on the predicted human CL, four methods were used to project the first-in-human dose. The predicted pharmacokinetic parameters and the estimated first-in-human dose of coagulation factors were compared with the observed human values obtained from clinical trials. The results of the study indicated that the CL of coagulation factors can be predicted with reasonable accuracy in humans and a good estimate of first-in-human dose can be obtained from the predicted human CL. The suggested methods in this study are not only time and cost-effective but also provide rational alternatives to the somewhat arbitrary dose selection process for coagulation factors often used.

Determination of antibiotic dosage adjustments in patients with renal impairment: elements for success

This report reviews a contemporary methodology for determining antibiotic dosage modifications among patients with renal impairment. Historically, the approach to identifying renal dosage adjustments has focused on achieving comparable concentration-time profiles between patients with renal impairment and those with normal kidney function. While this approach is intuitive, it fails to incorporate the relationship between antibiotic exposure and effect in the renal dose selection process. A candidate renal dosing scheme that is worthy of incorporation into clinical practice should balance the probability of achieving the exposure target associated with success against the risks of toxicity and the emergence of resistance. This review describes a methodology for optimally identifying dosage adjustments in patients with impaired renal function using extended-infusion piperacillin/tazobactam as an illustrative example.

Laboratory monitoring of low‐molecular‐weight heparin therapy

essayists single out three special groups for possible laboratory test-guided dosing. The first are patients with renal failure, the second are morbidly obese patients, and the third are women in the late stages of pregnancy. In all three circumstances, a reasonable argument can be made for using the result of an antifactor (F)Xa heparin assay to guide dose selection. In morbid obesity and stable renal disease, this dose selection process can be completed after one or two iterations, while in a less stable situation of pregnancy it may have to be continued until delivery. The estimates for the targeted anti-FXa levels provided in the reviews are based on indirect evidence, but are reasonable.

Pharmacokinetics and Concentration‐Effect Analysis of Intravenous RGD891, a Platelet GPIIb/IIIa Antagonist, Using Mixed‐Effects Modeling (NONMEM)

RGD891 is a platelet GPIIb/IIIa receptor antagonist and potent inhibitor of platelet aggregation. This compound is biotransformed in vivo to RGD039, which also exhibits high affinity for the GPIIb/IIIa receptor. Pharmacokinetic/pharmacodynamic modeling was employed to describe the concentration-effect relationship of both compounds following the intravenous administration of RGD891 to healthy volunteers. The overall objectives of this work were to support the dose selection process for future intravenous RGD891 safety and efficacy studies. Various intravenous regimens of RGD891 were administered to healthy volunteers enrolled in three Phase I studies. Frequent plasma samples were collected at regular intervals for later measurement of RGD891 and RGD039 concentrations (validated LC/MS/MS methods). The pharmacokinetics of RGD891 and RGD039 were simultaneously analyzed by nonlinear mixed-effect modeling (NONMEM). Pharmacodynamic activity was assessed in all three studies by the degree to which ADP (20 microM)-induced platelet aggregation was inhibited. Population parameters describing the concentration-effect relationship of RGD891 and RGD039 were then generated using a modified competitive Emax-based model. Parent compound is by far the predominant active compound circulating in the plasma following intravenous administration of RGD891. The plasma RGD891 concentration-time data were best fit by a two-compartment structural model. The fit of the basic model was improved when total body weight was introduced as a covariate for RGD891 distribution. Between-subject variability in the RGD891 pharmacokinetic parameters--V1, K10, and K21--was less than 17% (coefficient of variation). Formation of the active metabolite (RGD039; Km) and its elimination (Kem) were assumed to be first-order processes (i.e., one-compartment model). The population pharmacokinetic model could only provide a rough estimate of the plasma concentration-time profile for RGD039 after administration of a given intravenous dosage regimen of RGD891 since metabolite concentrations were relatively low and highly variable. The first-order rate constant describing the formation of RGD039 from RGD891 (Km) was also associated with a substantial degree of between-subject variability (44.9%). The potency of RGD891 toward the inhibition of ADP-induced platelet aggregation was described by the population IC50 value (plasma concentration yielding 50% of maximal inhibition), which ranged from 58.0 to 95.4 ng/mL, depending on the pharmacokinetic-pharmacodynamic (PK-PD) model and the data set used. The relatively low concentrations of the active metabolite achieved following intravenous administration of RGD891 did not permit independent estimation of a population IC50 value for RGD039. Therefore, its potency was fixed at 2.2-fold greater than that of the parent compound (based on previous PK-PD analyses). Intersubject variability in the IC50 values was 30%. Antagonism of the platelet IIb/IIIa receptors by intravenously administered RGD891 was effective in inhibiting ADP-induced platelet aggregation in a reversible and dose-dependent manner. Pharmacodynamic activity was largely attributed to the parent compound and less to the active metabolite based on the relative potencies of both compounds and the plasma concentrations of each achieved following intravenous administration. Intravenous bolus plus maintenance infusion regimens resulted in rapid attainment of steady-state plasma RGD891 concentrations. This combination regimen also provided for a marked and sustained inhibition of platelet aggregation that reached 90% or greater (relative to baseline values) in the higher dose groups. The modified Emax model adequately described inhibition of platelet aggregation following a particular intravenous dosage regimen of RGD891 (within the range of doses administered in the present studies). (ABSTRACT TRUNCATED)