Pharmacokinetic-Pharmacodynamic Comparison of Recombinant and Plasma-Derived von Willebrand Factor in Patients with von Willebrand Disease Type 3.

Background: Recombinant von Willebrand factor (rVWF, vonicog alfa, Vonvendi/Veyvondi, Takeda Pharmaceuticals USA, Lexington, MA) and several plasma-derived VWF/factor VIII (pdVWF/FVIII) concentrates are available for treating bleeding episodes in patients with von Willebrand disease (VWD). Purpose: To develop population pharmacokinetic (PK)/pharmacodynamic (PD) models that describe VWF:ristocetin cofactor (VWF:RCo) activity and its relationship with FVIII activity (FVIII:C) over time following intravenous administration of either rVWF or a pdVWF/FVIII concentrate (VWF:RCo/FVIII:C 2.4:1) in patients with VWD; to use the final PK/PD models for an in silico comparison of rVWF and pdVWF/FVIII. Methods: The population PK model for rVWF was based on data from four clinical studies in which rVWF was administered to adult patients with VWD type 1, 2 or 3 (phase 1: NCT00816660; phase 3: NCT01410227 and NCT02283268) or severe hemophilia A (phase 1: EudraCT 2011-004314-42). The PK and PK/PD models for pdVWF/FVIII were based on data from the phase 1 study (NCT00816660) in patients with type 3 VWD who received either rVWF plus recombinant FVIII (rFVIII, octocog alfa, ADVATE®, Takeda Pharmaceuticals USA, Lexington, MA, USA) or pdVWF/FVIII. Results: There was a marked difference in clearance following rVWF administration compared with pdVWF/FVIII in type 3 VWD, leading to a ~1.75 longer mean residence time (ie, persistence of VWF:RCo activity in the body) and half-life for rVWF versus pdVWF/FVIII. Simulations showed that following repeated administration of rVWF (50 IU/kg), a FVIII:C activity of >40 IU/dL can be maintained for the full 72 h dosing interval. Conclusion: The slower elimination of VWF:RCo following rVWF administration results in a prolonged effect on FVIII turnover compared with pdVWF/FVIII administration.

Critical Remarks on Reference-Scaled Average Bioequivalence.

PURPOSE: More than a decade ago the option to assess highly variable drugs / drug products by reference-scaled average bioequivalence was introduced in regulatory practice. Recommended approaches differ between jurisdictions and may lead to different conclusions even for the same data set. According to our knowledge, implemented methods have not been directly compared for their operating characteristics (Type I Error and power). METHODS: We performed Monte Carlo simulations to assess the consumer risk and the clinically relevant difference for the recommended regulatory settings. RESULTS: In all methods for reference-scaled average bioequivalence the Type I Error can be inflated with a consequently compromised consumer risk. Furthermore, the clinically relevant difference could vary between studies performed with the same reference product. CONCLUSIONS: Only average bioequivalence with fixed - widened - limits would both maintain the consumer risk and offer an unambiguously defined clinically not relevant difference. As long as such an approach is not implemented in regulatory practice, we recommend adjusting the level of the test a.

Assessment of pharmacokinetic linearity after repeated drug administration.

The prediction of drug concentration time courses after different dosing scenarios is greatly facilitated if the pharmacokinetics (PK) can be assumed linear. The assumption of linear PK thus needs careful evaluation for any new drug in development. Under linear PK, exposure is proportional to dose (linear PK across doses) and exposure at steady state can be predicted from a single dose based on the superposition principle (linear PK over time). While investigation of dose-proportionality is common practice, evaluation of time dependent PK has received less attention in the literature. In particular, the superposition principle can be used to assess whether the observed extent of accumulation after repeated administration is expected under the premise of linear PK. This work emphasizes the importance of the time related aspect of linear PK by introducing the predictability ratio (PR). Linear PK over time can be concluded if PR = 1. Accumulation is higher than expected if PR >1, and lower if PR <1. If PK data from multiple dose cohorts are available, the PR is assessed for each dose cohort and a supportive hypothesis test can be applied to test for potential differences between doses in PR.

Assessing goodness-of-fit for evaluation of dose-proportionality.

For the clinical development of a new drug, the determination of dose-proportionality is an essential part of the pharmacokinetic evaluations, which may provide early indications of non-linear pharmacokinetics and may help to identify sub-populations with divergent clearances. Prior to making any conclusions regarding dose-proportionality, the goodness-of-fit of the model must be assessed to evaluate the model performance. We propose the use of simulation-based visual predictive checks to improve the validity of dose-proportionality conclusions for complex designs. We provide an illustrative example and include a table to facilitate review by regulatory authorities.

Modeling to Predict Factor VIII Levels Associated with Zero Bleeds in Patients with Severe Hemophilia A Initiated on Tertiary Prophylaxis.

BACKGROUND: Factor VIII (FVIII) trough levels > 1 IU/dL in patients with severe hemophilia A receiving regular prophylaxis may optimize bleed protection. OBJECTIVES: In this post hoc analysis of patients receiving tertiary prophylaxis for approximately 1 year, the relationship between estimated FVIII levels and reported bleeds was investigated to predict the potential for zero bleeds. METHODS: Sixty-three patients (median [range] age, 28 [7-59] years) with severe hemophilia A (229 bleeds) were included. FVIII levels at time of each bleed were estimated from single-dose individual pharmacokinetics. The highest estimated FVIII level at which patients experienced a bleed was considered the "potentially effective trough level" for that bleed type. Kaplan-Meier estimates of proportions of patients with no bleeds above certain estimated FVIII levels were determined. Those not experiencing a bleed in the trial were assumed to have a bleed at 0 IU/dL (pragmatic approach) or at their median trough level (conservative approach). RESULTS: Kaplan-Meier estimates based on pragmatic approach predicted zero all bleeds, joint bleeds, and spontaneous joint bleeds in 1 year in 40, 43, and 63% of patients, respectively, when the potentially effective trough FVIII level was set at 1 IU/dL. Between 1 and 10 IU/dL, every 1 IU/dL rise in estimated FVIII level was associated with an additional 2% of patients having zero all bleeds. CONCLUSION: This post hoc analysis confirms benefits with trough levels of approximately 1 to 3 IU/dL in most patients starting tertiary prophylaxis; prophylaxis with higher trough levels may help patients to achieve zero bleeds.

The potential of the estimands framework for clinical pharmacology trials: Some discussion points.

The recently finalised and published guideline ICH E9 (R1) introduced a new framework for the statistical analysis of clinical trials, namely that of "estimands". While the framework was originally developed for the analysis of late-phase trials, it could also provide a rigorous basis for the analysis of clinical pharmacology trials. We illustrate potential applications on two examples: a multiple dose pharmacology trial and the interpretation of confirmatory bioequivalence (BE) trials according to the current FDA and EMA BE guidelines.

SHP656, a polysialylated recombinant factor VIII (PSA-rFVIII): First-in-human study evaluating safety, tolerability and pharmacokinetics in patients with severe haemophilia A.

INTRODUCTION: SHP656 is the first factor VIII (FVIII) product developed using polysialylation (PSA) technology, in which full-length recombinant (r) FVIII (anti-haemophilic factor [recombinant]) is conjugated with a 20 kDa PSA polymer. AIM: To compare the safety, immunogenicity and pharmacokinetics of SHP656 vs the parent rFVIII (octocog alfa) after single infusions of 25-75 IU/kg in patients with severe haemophilia A (FVIII activity <1%). METHODS: Multinational, phase 1, prospective, open-label, two-period, fixed-sequence, dose-escalation trial (clinicaltrials.gov NCT02716194). Patients received single doses of rFVIII and then SHP656 sequentially at the same dose: 25 ± 3 IU/kg (Cohort 1), 50 ± 5 IU/kg (Cohort 2) and 75 ± 5 IU/kg (Cohort 3). RESULTS: Forty patients received rFVIII: 11 in Cohort 1, 16 in Cohort 2 and 13 in Cohort 3. Two patients withdrew before receiving SHP656, leaving 38 patients who completed the study and received both treatments. No treatment-related adverse events (AEs), serious AEs, deaths, study withdrawals, thrombotic events or allergic reactions were reported; and no significant treatment-related changes in laboratory parameters or vital signs. No patients developed FVIII inhibitors or antibodies to PSA. FVIII activity was significantly prolonged following SHP656 administration vs rFVIII with an approximately 1.5-fold extension in mean residence time (P < .05). Exposure increased proportional to the SHP656 dose over the 25-75 IU/kg dose range. CONCLUSION: Polysialylation of rFVIII confers a half-life extension similar to that of approved extended half-life products that use either PEGylation or Fc fusion technology and was not associated with any treatment-related adverse events.

Evaluation of Factor VIII Polysialylation: Identification of a Longer-Acting Experimental Therapy in Mice and Monkeys.

Extended half-life (EHL) factor therapies are needed to reduce the burden of prophylaxis and improve treatment adherence in patients with hemophilia. BAX 826 is a novel polysialylated full-length recombinant factor VIII [polysialyic acid (PSA) rFVIII] with improved pharmacokinetics (PK), prolonged pharmacology, and maintained safety attributes to enable longer-acting rFVIII therapy. In factor VIII (FVIII)-deficient hemophilic mice, PSArFVIII showed a substantially higher mean residence time (>2-fold) and exposure (>3-fold), and prolonged efficacy in tail-bleeding experiments (48 vs. 30 hours) compared with unmodified recombinant FVIII (rFVIII), as well as a potentially favorable immunogenicity profile. Reduced binding to a scavenger receptor (low-density lipoprotein receptor-related protein 1) and von Willebrand factor (VWF) as well as a largely VWF-independent circulation time in mice provide a rationale for prolonged BAX 826 activity. The significantly improved PK profile versus rFVIII was confirmed in cynomolgus monkeys [mean residence time: 23.4 vs. 10.1 hours; exposure (area under the curve from time 0 to infinity): 206 vs. 48.2 IU/ml⋅h] and is in line with results from rodent studies. Finally, safety and toxicity evaluations did not indicate increased thrombogenic potential, and repeated administration of BAX 826 to monkeys and rats was well tolerated. The favorable profile and mechanism of this novel experimental therapeutic demonstrated all of the requirements for an EHL-rFVIII candidate, and thus BAX 826 was entered into clinical assessment for the treatment of hemophilia A. SIGNIFICANCE STATEMENT: Prolongation of FVIII half-life aims to reduce the burden of prophylaxis and improve treatment outcomes in patients with hemophilia. This study shows that polysialylation of PSArFVIII resulted in prolongations of rFVIII circulation time and procoagulant activity, together with a favorable nonclinical safety profile of the experimental therapeutic.

Population pharmacokinetic modeling and simulation of immunoglobulin exposure with varying dosing intervals of subcutaneous immunoglobulin 20% (Ig20Gly) in patients with primary immunodeficiency diseases.

BACKGROUND: Immunoglobulin (IG) replacement therapy in patients with primary immunodeficiency diseases (PID) can be administered daily to every 2 weeks subcutaneously (SCIG) or every 3 or 4 weeks intravenously (IVIG). OBJECTIVES: Develop a population pharmacokinetic (PK) model simulating IG exposure with Ig20Gly, a 20% SCIG; determine the dose adjustment factor for Ig20Gly relative to IVIG. METHODS: Data from patients with PID treated with Ig20Gly and IVIG 10% were used to characterize IG population PK by nonlinear mixed-effects modeling and validated using data splitting and a visual predictive check. IG profiles were simulated for 1000 patients/interval treated with Ig20Gly (daily, every 2 days, every 3 days, twice weekly, weekly, every 2 weeks). An Ig20Gly adjustment factor of 130% was used to simulate Ig20Gly to IVIG AUC ratios for weekly or every 2 weeks Ig20Gly dosing intervals and a monthly IVIG dosing interval. RESULTS: A 1-compartment model, using weight as a covariate on clearance, derived from an index modeling dataset (n = 81) demonstrated predictability for a validation dataset (n = 21). The model estimate of bioavailability was 73.9%. Simulations for 6 dosing intervals showed similar mean profiles with overlapping prediction intervals. Mean AUC ratios of Ig20Gly to IVIG with a dose adjustment factor of 1.30:1 were 98.7% for weekly and 97.7% for twice-weekly administration demonstrating comparable exposure. CONCLUSION: Ig20Gly exposures from daily to up to every 2 weeks appeared equivalent. A 1.30 conversion factor provided coverage comparable to IVIG when Ig20Gly is administered daily to every 2 weeks.

Pharmacokinetics, disease-modifying activity, and safety of an experimental therapeutic targeting an immunological isoform of macrophage migration inhibitory factor, in rat glomerulonephritis.

New therapeutic agents are needed to overcome the toxicity and suboptimal efficacy observed in current treatment of glomerulonephritis (GN). BaxB01 is a fully human monoclonal antibody targeting a disease-related immunologically distinct isoform of Macrophage migration Inhibitory Factor (MIF), designated oxidized MIF (oxMIF) and locally expressed in inflammatory conditions. We report the pharmacokinetic profile of BaxB01, and its dose and exposure-related disease-modifying activity in experimentally induced rat GN. BaxB01 bound to rat oxMIF with high affinity and reduced rat macrophage migration in vitro. After intravenous administration in rats, BaxB01 demonstrated favorable pharmacokinetics, with a half-life of up to nine days. Disease modification was dose-related (≥ 10mg/kg) as demonstrated by significantly reduced proteinuria and diminished histopathological glomerular crescent formation. Importantly, a single dose was sufficient to establish an exposure-related, anti-inflammatory milieu via amelioration of glomerular cellular inflammation. Pharmacodynamic modeling corroborated these findings, consistently predicting plasma exposures that were effective in attenuating both anti-inflammatory activity and reducing loss of kidney function. This pharmacologic benefit on glomerular function and structure was sustained during established disease, while correlation analyses confirmed a link between the antibody's anti-inflammatory activity and reduced crescent formation in individual rats. Finally, safety assessment in rats showed that the experimental therapeutic was well tolerated without signs of systemic toxicity or negative impact on kidney function. These data define therapeutically relevant exposures correlated with mechanism-based activity in GN, while toxicological evaluation suggests a large therapeutic index and provides evidence for achieving safe and effective exposure to a MIF isoform-directed therapeutic in nephritis-associated disease.

Adjustment of endogenous concentrations in pharmacokinetic modeling.

PURPOSE: Estimating pharmacokinetic parameters in the presence of an endogenous concentration is not straightforward as cross-reactivity in the analytical methodology prevents differentiation between endogenous and dose-related exogenous concentrations. This article proposes a novel intuitive modeling approach which adequately adjusts for the endogenous concentration. METHODS: Monte Carlo simulations were carried out based on a two-compartment population pharmacokinetic (PK) model fitted to real data following intravenous administration. A constant and a proportional error model were assumed. The performance of the novel model and the method of straightforward subtraction of the observed baseline concentration from post-dose concentrations were compared in terms of terminal half-life, area under the curve from 0 to infinity, and mean residence time. RESULTS: Mean bias in PK parameters was up to 4.5 times better with the novel model assuming a constant error model and up to 6.5 times better assuming a proportional error model. CONCLUSIONS: The simulation study indicates that this novel modeling approach results in less biased and more accurate PK estimates than straightforward subtraction of the observed baseline concentration and overcomes the limitations of previously published approaches.

Thrombin based gelatin matrix and fibrin sealant mediated clot formation in the presence of clopidogrel.

BACKGROUND: Platelet inhibitors are commonly used to reduce the risk of atherothrombotic events. The aim of this study was to determine the impact of platelet inhibitors, specifically clopidogrel and aspirin, on clot kinetics, strength, and/or structure during the use of thrombin based gelatin matrices and fibrin sealants. METHODS: Blood was collected and heparinized from donors on clopidogrel (and aspirin) and age matched control donors. Blood component analysis, whole blood platelet aggregometry, and activated clotting time (ACT) were used to monitor compliance to therapy and identify any differences between donor groups. Clot kinetics and strength were analyzed using thrombelastography (TEG). Field Emission Scanning Electron Microscopy (FESEM) was used to analyze clot structure. RESULTS: Blood component profiles were similar for both donor groups. Aggregometry indicated that aggregation response to adenosine diphosphate (ADP) for clopidogrel donors was 12% of that for the controls (p = 0.0021), an expected result of clopidogrel induced platelet inhibition. However, blood from both donor groups had an elevated thrombin induced aggregation response. Heparinization of donor blood resulted in similarly elevated ACTs for both donor groups. TEG results indicated similar clot kinetics and strength between clopidogrel and control donor groups for blood alone and when clotting was induced using thrombin based gelatin matrices and fibrin sealants. FESEM images supported TEG findings in that similar morphologies were observed in ex vivo formed clots from both donor groups when thrombin based gelatin matrices and fibrin sealants were used. CONCLUSION: These results suggest that platelet inhibitors do not negatively impact clot kinetics, strength, and structure when clotting is initiated with thrombin based gelatin matrices and fibrin sealants.

Randomized, controlled comparison of advanced hemostatic pads in hepatic surgical models.

Blood loss during hepatic surgery leads to poor patient outcomes. This study investigates the hemostatic efficacy of a novel sealing hemostatic pad (polyethylene glycol-coated collagen, PCC) and a fibrin sealant pad (fibrin-thrombin coated collagen, FTC) in a leporine hepatic segmentectomy and a porcine hepatic abrasion model. A segmentectomy was used to compare hemostatic success and hematoma incidence in 20 rabbits (10/group). Hepatic abrasions were used to compare hemostatic success up to 10 min after application in six pigs (42 lesions/group). In the segmentectomy model, PCC achieved 100% hemostatic success within 2 min (95% CI: 72.3% to 100%) and FTC achieved 80% hemostatic success within 3 min (49.0% to 94.3%). PCC had lower hematoma incidence at 15 min (0.0 versus 11.1%) and 24 h (20.0 versus 66.7%). In the abrasion model, PCC provided superior hemostatic success at 3 (odds ratio: 24.8, 95% CI: 8.86 to 69.2, P < 0.001), 5 (66.3, 28.5 to 153.9, P < 0.001), 7 (177.5, 64.4 to 489.1, P < 0.001), and 10 min (777.6, 148.2 to 4078, P < 0.001) leading to statistically significant less blood loss. The novel sealing hemostat provides faster and more sustained hemostasis than a fibrin sealant pad in a leporine hepatic segmentectomy and a porcine hepatic abrasion model of hepatic surgery.

A hybrid method to estimate the minimum effective dose for monotone and non-monotone dose-response relationships.

This article proposes a new multiple-testing approach for estimation of the minimum effective dose allowing for non-monotonous dose-response shapes. The presented approach combines the advantages of two commonly used methods. It is shown that the new approach controls the error rate of underestimating the true minimum effective dose. Monte Carlo simulations indicate that the proposed method outperforms alternative methods in many cases and is only marginally worse in the remaining situations.

A comparison of methods for classifying samples as truly specific with confirmatory immunoassays.

Biotechnology-derived therapeutics may induce an unwanted immune response leading to the formation of anti-drug antibodies (ADAs) which can result in altered efficacy and safety of the therapeutic protein. Anti-drug antibodies may, for example, affect pharmacokinetics of the therapeutic protein or induce autoimmunity. It is therefore crucial to have assays available for the detection and characterization of ADAs. Commonly, a screening assay is initially used to classify samples as either ADA positive or negative. A confirmatory assay, typically based on antigen competition, is subsequently employed to separate false positive samples from truly positive samples. In this manuscript we investigate the performance of different statistical methods classifying samples in competition assays through simulation and analysis of real data. In our evaluations we do not find a uniformly best method although a simple t-test does provide good results throughout. More crucially we find that very large differences between uninhibited and inhibited measurements relative to the assay variability are required in order to obtain useful classification results questioning the usefulness of competition assays with high variability.

Estimation in AB/BA crossover trials with application to bioequivalence studies with incomplete and complete data designs.

Crossover studies are frequently used in clinical research as they allow within-subject comparisons instead of the between-subject evaluation of parallel group designs. Estimation of interesting parameters from such designs is, however, not trivial. We provide three methods for estimating treatment effects and associated standard errors from an AB/BA crossover trial. Assuming at least asymptotic normality, we can obtain the confidence intervals for single parameters as well as for differences or ratios of treatment effects. The latter is particularly useful in a pharmacokinetic context to establish bioequivalence using area under the concentration versus time curves (AUCs). In this work, we will illustrate how Fieller-type confidence intervals can be constructed for the ratio of AUCs estimated using a noncompartmental approach in a sparse sampling setting from a two-treatment, two-period, two-sequence crossover trial. In particular, we will discuss a flexible batch design, which includes traditional serial sampling and complete data designs as special cases. Via simulation, we show that the proposed intervals have nominal coverage and keep the type I error even for small sample sizes. Moreover, we illustrate the methodology in a real data example.

Distinct characteristics of antibody responses against factor VIII in healthy individuals and in different cohorts of hemophilia A patients.

Neutralizing antibodies against factor VIII (FVIII) remain the major complication in the replacement therapy of hemophilia A patients. To better understand the evolution of these antibodies it is important to generate comprehensive datasets which include both neutralizing and nonneutralizing antibodies, their isotypes, and IgG subclasses. We developed sensitive ELISAs to analyze FVIII-binding antibodies in different cohorts of hemophilia A patients and in healthy individuals. Our data reveal the prevalence of FVIII-binding antibodies among healthy individuals (n = 600) to be as high as 19%, with a prevalence of antibody titers > or =1:80 of 2%. The prevalence of FVIII-binding antibodies was 34% (5% for titers > or =1:80) in patients without FVIII inhibitors (n = 77), 39% (4% for titers > 1:80) in patients after successful immune tolerance induction therapy (n = 23), and 100% (n = 20, all titers > or =1:80) in patients with FVIII inhibitors. We found significant differences for IgG subclasses of FVIII-binding antibodies between the different study cohorts. IgG4 and IgG1 were the most abundant IgG subclasses in patients with FVIII inhibitors. Strikingly, IgG4 was completely absent in patients without FVIII inhibitors and in healthy subjects. These findings point toward a distinct immune regulatory pathway responsible for the development of FVIII-specific IgG4 associated with FVIII inhibitors.

Non-compartmental estimation of pharmacokinetic parameters for flexible sampling designs.

Pharmacokinetic (PK) studies aim to understand the kinetics of absorption, distribution, metabolism and elimination of a drug. Typically, such studies involve measuring the concentration of the drug in the plasma or blood at several time points after drug administration. In studying the PK behaviour, either the non-compartmental approach or alternatively a modelling approach can be utilized. Traditionally, the non-compartmental approach makes minimal assumptions about the data-generating process but requires the data to be collected in a very structured way. Conversely, the modelling approach depends heavily on assumptions about the data-generating process but does not impose a specific data structure. In this paper, we will discuss non-compartmental methods for estimating the area under the concentration versus time curve and other common PK parameters that use minimal assumptions about the data structure making it applicable to a wide range of PK studies. We will evaluate the methods using simulation and give an illustrative example.

A formal comparison of different methods for establishing cut points to distinguish positive and negative samples in immunoassays.

Biotechnology derived therapeutics may induce an unwanted immune response leading to the formation of anti-drug antibodies (ADA). As a result the efficacy and safety of the therapeutic protein could be impaired. Neutralizing antibodies may, for example, affect pharmacokinetics of the therapeutic protein or induce autoimmunity. Therefore a drug induced immune response is a major concern and needs to be assessed during drug development. It is therefore crucial to have assays available for the detection and characterization of ADAs. These assays are used to classify samples in positive and negative samples based on a cut point. In this manuscript we investigate the performance of established and newly developed methods to determine a cut point in immunoassays such as ELISA through simulation and analysis of real data. The different methods are found to have different advantages and disadvantages. A robust parametric approach generally resulted in very good results and can be recommended for many situations. The newly introduced method based on mixture models yields similar results to the robust parametric approach but offers some additional flexibility at the expense of higher complexity.