Exposure-Bleeding Count Modeling of Emicizumab for the Prophylaxis of Bleeding in Persons with Hemophilia A with/Without Inhibitors Against Factor VIII

Automated Poisson regression exposure-response analysis for binary outcomes with PoissonERM

PoissonERM is an R package used to conduct exposure-response (ER) analysis on binary outcomes for establishing the relationship between exposure and the occurrence of adverse events (AE). While Poisson regression could be implemented with glm(), PoissonERM provides a simple way to semi-automate the entire analysis and generate an abbreviated report as an R markdown (Rmd) file that includes the essential analysis details with brief conclusions. PoissonERM processes the provided data set using the information from the user's control script and generates summary tables/figures for the exposure metrics, covariates, and event counts of each endpoint (each type of AE). After checking the incidence rate of each AE, the correlation, and missing values in each covariate, an exposure-response model is developed for each endpoint based on the provided specifications. PoissonERM has the flexibility to incorporate and compare multiple scale transformations in its modeling. The best exposure metric is selected based on a univariate model's p-value or deviance (Δ D ) as specified. If a covariate search is specified in the control script, the final model is developed using backward elimination. PoissonERM identifies and avoids highly correlated covariates in the final model development of each endpoint. Predicting event incidence rates using external (simulated) exposure metric data is an additional functionality in PoissonERM, which is useful to understand the event occurrence associated with certain dose regimens. The summary outputs of the cleaned data, model developments, and predictions are saved in the working folder and can be compiled into a HTML report using Rmd.

Transitioning from emicizumab prophylaxis to valoctocogene roxaparvovec gene therapy: A simulation study for individuals with severe haemophilia A

INTRODUCTION

Valoctocogene roxaparvovec, a gene therapy evaluated in the phase 3 GENEr8-1 trial, supports endogenous factor VIII (FVIII) production to prevent bleeding in people with severe haemophilia A. Individuals receiving emicizumab, an antibody mimicking the function of activated FVIII, were excluded from GENEr8-1 enrolment since emicizumab was an investigational therapy at the time of trial initiation.

AIM

Utilize pharmacokinetic simulations to provide guidance on best practices for maintaining haemostatic control while transitioning from emicizumab prophylaxis to valoctocogene roxaparvovec.

METHODS

To estimate bleeding risk at weekly intervals following valoctocogene roxaparvovec infusion, a published emicizumab pharmacokinetic model was used to simulate emicizumab concentrations and merged with FVIII activity time-course data for participants in GENEr8-1. The analysis investigated three approved emicizumab dosing regimens for two transition scenarios that varied whether the last dose of emicizumab was administered on the same day or 4 weeks after valoctocogene roxaparvovec infusion.

RESULTS

Simulations demonstrated administering the last emicizumab dose the day of valoctocogene roxaparvovec infusion and 4 weeks after offered similar levels of haemostatic control, and bleeding risk was similar for all emicizumab dosing regimens. An algorithm was developed to provide guidance for discontinuation of emicizumab. Theoretical cases based on GENEr8-1 participants are presented to illustrate how decisions may vary among individuals.

CONCLUSION

Pharmacokinetic simulations demonstrated no clinically meaningful difference in bleeding risk caused by decaying emicizumab levels and rising gene therapy-derived endogenous FVIII for all examined emicizumab doses and dosing regimens. Therefore, multiple approaches can safely transition individuals from emicizumab prophylaxis to valoctocogene roxaparvovec.

Clinical pharmacology of emicizumab for the treatment of hemophilia A

INTRODUCTION

Emicizumab is a humanized bispecific antibody approved for the routine prophylaxis of bleeding episodes in patients with hemophilia A (PwHA) regardless of the presence of factor VIII (FVIII) inhibitors. It mimics the cofactor function of missing activated FVIII by bridging activated factor IX and factor X, thereby restoring hemostasis.

AREAS COVERED

This review covers the clinical pharmacology of emicizumab and the translation of its pharmacokinetics (PK) and pharmacodynamics (PD) to clinical efficacy and safety. The PK of emicizumab is linear, with an approximately 1-month half-life. Once-weekly to every-4-week subcutaneous (SC) administrations maintain effective trough concentrations throughout the dosing intervals, associated with a coagulation potential analogous to that in patients with mild hemophilia A. In combination with activated prothrombin complex concentrate, and to a lesser extent with recombinant activated factor VII, emicizumab exerts a synergistic effect, whereas combination with FVIII may result in a non-additive coagulation potential at normal FVIII activity.

EXPERT OPINION

The translation of emicizumab PK/PD into clinical effects was demonstrated in several phase III studies, which showed remarkable bleed control and a favorable safety profile in PwHA. These emicizumab attributes, together with the convenience of use (infrequent SC injections), offer a novel paradigm for the management of PwHA.

DosEmi study protocol: a phase IV, multicentre, open-label, crossover study to evaluate non-inferiority of pharmacokinetic-guided reduced dosing compared with conventional dosing of emicizumab in people with haemophilia A

INTRODUCTION

Emicizumab effectively prevents bleeding in people with haemophilia A (PwHA), but is a burden for national healthcare budgets and consequently may limit access. According to the drug label, dosing of emicizumab is based on body weight with fixed intervals of 7, 14 or 28 days, which leads to mean plasma concentrations of 55 µg/mL (SD 15 µg/mL). However, a moderate variability of concentrations and a minimal effective concentration of 30 µg/mL have been suggested in studies. Therefore, a dose of emicizumab that targets a trough concentration of 30 µg/mL is hypothesised to be equally effective as conventional dosing in the prevention of bleeding.

METHODS AND ANALYSIS

We designed a phase IV, multicentre, open-label, crossover study to evaluate non-inferiority of bleed control of ≥6 months on conventional dosing in comparison to ≥6 months on dose intervention. This dose intervention consists of reducing the dose of emicizumab to target a trough concentrations of 30 µg/mL using individual pharmacokinetic (PK) parameters. Ninety-five PwHA aged >1 years who received conventional dosing of emicizumab for ≥12 months with good bleeding control during the last 6 months will be recruited from all Dutch haemophilia treatment centres. The study is powered to detect a clinically relevant decrease (risk difference) of 15% in the proportion of patients without treated bleeds during follow-up. Secondary endpoints are spontaneous joint or muscle bleeds, and annualised treated bleeding rates (using negative binomial regression). Cost-effectivity between conventional dosing and individualised PK-guided dosing of emicizumab will be compared.

ETHICS AND DISSEMINATION

The DosEmi study was approved by the Medical Ethics Review Committee NedMec of the University Medical Center of Utrecht, The Netherlands. Study results will be communicated through publications in international scientific journals and presentations at (inter)national conferences.

TRIAL REGISTRATION NUMBER

EUCTR2021-004039-10-NL at https://trialsearch.who.int.

PROTOCOL VERSION

V.4.1 on 28 October 2022 (DosEmi protocol_V4.1; NL81112.041.22).

Decrease in in vivo coagulant potential of emicizumab in a patient with hemophilia A and inhibitor complicated with infectious mononucleosis

Emicizumab prophylaxis significantly reduces bleeding episodes in patients with hemophilia A (PwHA). There is little information on coagulant potentials in emicizumab-treated PwHA with infection, however. We encountered an emicizumab-treated PwHA with inhibitor, complicated with Epstein-Barr virus-associated infectious mononucleosis (IM) in phase 1/2 study (ACE001JP/ACE002JP). Although it was a typical clinical course of IM, activated partial thromboplastin time was mildly prolonged but rotational thromboelastometry revealed severely impaired coagulant potential. The blood concentration of emicizumab decreased moderately in the low concentration range, resulting in an increased risk of bleeding and possibly leading to severe ileocecal bleeds requiring coil embolization. The blood concentrations of factors IX/X little decreased and antiemicizumab antibodies did not develop, however. After the influence by IM resolved, his coagulant potentials gradually recovered with the recovery of emicizumab concentration, and parameters by global coagulation assays improved. An IM case for emicizumab-treated PwHA may need to monitor using global coagulation assays.

A prospective, multicenter, open-label phase III study of emicizumab prophylaxis in patients with acquired hemophilia A

BACKGROUND

Emicizumab is a bispecific antibody that mimics the cofactor function of activated factor (F) VIII. It prevents bleeds in patients with congenital hemophilia A regardless of the inhibitor status; however, no prospective clinical studies have been conducted for emicizumab in patients with acquired hemophilia A (PwAHA).

OBJECTIVES

To describe the primary analysis results from a prospective, multicenter, open-label phase III study evaluating the efficacy, safety, and pharmacokinetics of emicizumab in PwAHA (AGEHA; JapicCTI-205151).

METHODS

Emicizumab was administered subcutaneously at 6 mg/kg on day 1 and 3 mg/kg on day 2, followed by 1.5 mg/kg once weekly from day 8 onward. Predefined criteria for the completion of dosing included FVIII activity of >50 IU/dL.

RESULTS

By the cutoff date (April 23, 2021), 12 patients on immunosuppressive therapy were enrolled, and 11 of them (91.7%) completed emicizumab treatment. The mean trough plasma emicizumab concentration rapidly reached a steady state (1 week), achieving the efficacious level that was established in patients with congenital hemophilia A (>30 μg/mL). Before first emicizumab administration, 7 patients (58.3%) experienced 77 major bleeds. During emicizumab treatment, no major bleeds occurred in any patient. Neither death due to bleeding or infection nor any study treatment-related serious adverse event was reported. One asymptomatic, nonserious deep vein thrombosis was discovered with no laboratory findings indicating any trend toward hypercoagulation.

CONCLUSION

These results suggest that emicizumab prophylaxis with the tested dosing regimen and completion criteria may have a favorable benefit-risk profile in PwAHA.

Efficacy of emicizumab is maintained throughout dosing intervals for bleed prophylaxis

Background

Across the HAVEN clinical trial program, the efficacy of emicizumab has been demonstrated in children, adolescents, and adults with hemophilia A, with or without factor VIII inhibitors. After the 4-week loading dose period, emicizumab concentrations are expected to remain at levels that provide bleed protection throughout the entire dosing interval, regardless of the chosen maintenance dosing regimen, ie, weekly, every 2 weeks, or every 4 weeks.

Objectives

The objective of this study was to examine the timing of treated bleeds within the dosing intervals for emicizumab administered during the HAVEN 1 to 4 studies.

Methods

In this post hoc analysis, we pooled data from all the participants of the HAVEN 1 to 4 studies and analyzed the timing of treated bleeds in relation to the emicizumab dose.

Results

A total of 392 participants were included in this analysis, with a median (range) age of 28.0 years (1.1-77.0 years). Target joints were identified in 237 of 392 (60.5%) participants before the study entry. Overall, 211 of 392 (53.8%) participants experienced 907 treated bleeding events. The total mean (SD) annualized bleeding rate across the 4 studies was 1.6 (5.9). There was no evidence that bleeding events clustered on any 1 particular day in any dosing schedule from HAVEN 1 to 4 (P > .05 for all 3 treatment regimens).

Conclusion

Data from the HAVEN 1 to 4 trials show consistent bleed prevention within the dosing interval, regardless of the dosing regimen chosen. These findings provide further evidence of the sustained efficacy of emicizumab across all approved dosing regimens to reduce bleeding in people with hemophilia A.

Emicizumab dose up-titration in case of suboptimal bleeding control in people with haemophilia A

INTRODUCTION

Emicizumab promotes effective haemostasis in people with haemophilia A (PwHA). It is indicated for routine prophylaxis of bleeding episodes in PwHA with or without factor (F)VIII inhibitors.

AIM

To investigate the effect of emicizumab dose up-titration in PwHA with suboptimal bleeding control.

METHODS

Data from seven completed or ongoing phase III studies were pooled. Pharmacokinetics, pharmacodynamics and bleeding events were evaluated before and after dose up-titration. Adverse events (AEs) were compared between PwHA with and without dose up-titration.

RESULTS

Of 675 PwHA evaluable for the analysis, 24 (3.6%) had their maintenance dose up-titrated to 3 mg/kg once weekly (QW). Two participants had neutralising antibodies (nAbs) associated with decreased emicizumab exposure, and dose increase did not compensate for the effect of nAbs. In the other 22 participants, mean emicizumab steady-state trough concentrations increased from 44.0 to 86.2 μg/mL after up-titration. The median (interquartile range [IQR]) efficacy period prior to up-titration was 24.6 (24.0-32.0) weeks. The model-based annualised bleed rate for 'treated bleeds' and 'all bleeds' decreased by 70.2% and 72.9%, respectively, after a median (IQR) follow-up of 97.1 (48.4-123.3) weeks in the up-titration period. Incidences of injection-site reactions and serious AEs were higher in PwHA with up-titration; however, this was already observed in these participants before the dose up-titration. Overall, the safety profile appeared similar between PwHA with and without up-titration.

CONCLUSION

The dose up-titration to 3 mg/kg QW was well tolerated. Bleed control improved in most participants whose bleeding tendency was inadequately controlled during clinical trials.

Optimizing maintenance dosing of emicizumab-kxwh as prophylaxis in hemophilia A: Dosing to product labeling while minimizing drug waste

BACKGROUND: The introduction of the bispecific antibody emicizumab-kxwh has driven a paradigm shift in the management of patients with hemophilia A. Emicizumab-kxwh is gradually replacing factor VIII as the treatment of choice for prophylaxis. The requirement to dose emicizumab-kxwh by weight can drive waste when the appropriate combination of various strengths of single-use vials is not considered, whereas inappropriate rounding to full vials can lead to significantly subtherapeutic or supratherapeutic doses. OBJECTIVE: To quantify waste reduction and impact to savings when a clinical program designed to optimize the emicizumab-kxwh dose, frequency, and vial combination is applied at the dispensing specialty pharmacy level. METHODS: The electronic medical records of 360 patients receiving emicizumab-kxwh as maintenance therapy were retrospectively reviewed. Patients were included in the sample if they were male, were aged 18 to 89 years, were inhibitor negative, and had at least 1 new or renewal maintenance prescription in 2021. Three hundred seventy discrete regimens were identified as evaluated per the Regimen Optimization Algorithm - emicizumab-kxwh and included in the final sample. Data collected for each regimen included patient weight, emicizumab-kxwh dose and interval originally prescribed, every 7-day equivalent regimen (to the hundredth of a milligram), vial combination originally ordered, and resulting waste generated. For those regimens failing the algorithm, additional review of pharmacist follow-up and prescriber engagement was performed. When the prescriber adopted a pharmacist recommendation to adjust dose, frequency of administration and/or vial combination, impact to cost was calculated (Medicare Part B 2022 average sale price). RESULTS: 48% (176/370) of reviewed regimens failed specialty pharmacist review because they drove a potentially subtherapeutic or supratherapeutic dose and/or resulted in the use of partial vials that required that the patient discard all emicizumab-kxwh over the prescribed amount with each dose. 112 (64%) of these failed regimens met full criteria for prescriber engagement to recommend a regimen adjustment to dose, frequency of administration, and/or vial combination. These recommendations were adopted in 43% of cases (48/112), resulting in a cumulative savings of 600 mg per dose while also avoiding significant subtherapeutic or supratherapeutic dosing. When factoring in the frequency of administration at the patient level, cumulative annual savings to payers across these 48 accepted recommendations was $1,793,549.76. CONCLUSIONS: These data illustrate that the application of an evidence-based Regimen Optimization Algorithm at the dispensing specialty pharmacy level can reduce waste and drive payer savings while avoiding significant subtherapeutic or supratherapeutic dosing. DISCLOSURES: Accredo, Inc, a specialty pharmacy dispensing emicizumab-kxwh to patients with hemophilia A, employs the authors. Accredo, Inc, is a subsidiary of EverNorth, which also includes Express Scripts, a PBM that adjudicates a portion of emicizumab-kxwh claims.

Safety and efficacy of long-term emicizumab prophylaxis in hemophilia A with factor VIII inhibitors: A phase 3b, multicenter, single-arm study (STASEY)

Background

The bispecific monoclonal antibody emicizumab bridges activated factor IX and factor X, mimicking the cofactor function of activated factor VIII (FVIII), restoring hemostasis.

Objectives

The Phase 3b STASEY study was designed to assess the safety of emicizumab prophylaxis in people with hemophilia A (HA) with FVIII inhibitors.

Methods

People with HA received 3 mg/kg emicizumab once weekly (QW) for 4 weeks followed by 1.5 mg/kg QW for 2 years. The primary objective was the safety of emicizumab prophylaxis, including incidence and severity of adverse events (AEs) and AEs of special interest (thrombotic events [TEs] and thrombotic microangiopathies). Secondary objectives included efficacy (annualized bleed rates [ABRs]).

Results

Overall, 195 participants were enrolled; 193 received emicizumab. The median (range) duration of exposure was 103.1 (1.1-108.3) weeks. Seven (3.6%) participants discontinued emicizumab. The most common AEs were arthralgia (n = 33, 17.1%) and nasopharyngitis (n = 30, 15.5%). The most common treatment-related AE was injection-site reaction (n = 19, 9.8%). Two fatalities were reported (polytrauma with fatal head injuries and abdominal compartment syndrome); both were deemed unrelated to emicizumab by study investigators. Two TEs occurred (myocardial infarction and localized clot following tooth extraction), also deemed unrelated to emicizumab. The negative binomial regression model-based ABR (95% confidence interval) for treated bleeds was 0.5 (0.27-0.89). Overall, 161 participants (82.6%) had zero treated bleeds.

Conclusions

The safety profile of emicizumab prophylaxis was confirmed in a large population of people with HA with FVIII inhibitors and no new safety signals occurred. The majority of participants had zero treated bleeds.

Emicizumab in children: bleeding episodes and outcome before and after transition to Emicizumab

PURPOSE

Real-world data and study data regarding therapy with Emicizumab in pediatric cohorts with haemophilia A is scarce. Especially, data on previously untreated pediatric patients (PUPs) and minimally treated patients (MTPs) are missing.

METHODS

Thirteen pediatric patients with haemophilia A and treatment with Emicizumab were retrospectively evaluated for Annual Bleeding Rates (ABR) pre-and post-Emicizumab treatment. Safety data and data on management of minor surgery as well as laboratory results were collected. Additionally, we describe the clinical features of two PUPs and one MTP that are included in our cohort.

RESULTS

Median age at initiation of Emicizumab was 5.3 (range: 0.26-17.5) years, three patients were younger than one year at initiation of treatment with Emicizumab. Median follow-up time on Emicizumab was 23.8 (range: 0.7-40) months. Total ABR (p = 0.009) as well as spontaneous (p = 0.018), traumatic (p = 0.018), and joint (p = 0.027) ABR reduced significantly post-Emicizumab transition. Safety profile was favourable as only one local site reaction occurred; no cessation of treatment was necessary. Surgery was successfully performed in three patients receiving rFVlla pre- and post-surgery. Emicizumab trough levels showed a median of 43.2 μg/ml (range: 23.9-56.8) after three doses of 3 mg/kg and 51.9 μg/ml (range: 30.4-75) at first follow-up with 1.5 mg/kg.

CONCLUSION

Emicizumab is safe and efficient in pediatric patients with and without inhibitors. More data on larger multicenter cohorts and especially on PUPs/MTPs are still needed.

Prophylactic emicizumab for hemophilia A in the Asia-Pacific region: A randomized study (HAVEN 5)

Background

Emicizumab is a subcutaneously administered humanized, bispecific, monoclonal antibody approved for prophylaxis in people with hemophilia A.

Methods

HAVEN 5 (NCT03315455) is a randomized, open-label, phase 3 study of individuals aged ≥12 years with severe hemophilia A without factor VIII (FVIII) inhibitors, or hemophilia A of any severity with FVIII inhibitors, across the Asia-Pacific region. Participants were randomly assigned (2:2:1) to receive emicizumab 1.5 mg/kg once weekly (arm A), emicizumab 6 mg/kg every 4 weeks (arm B), or no prophylaxis (arm C). The primary end point was annualized bleeding rate (ABR) for treated bleeds; ABRs were compared between people receiving emicizumab prophylaxis versus those with no prophylaxis. Secondary end points included ABR for treated target joint bleeds. Safety was also evaluated.

Results

From April 26, 2018, to January 4, 2019, 70 of 76 screened participants were enrolled and randomized (arm A, n = 29; arm B, n = 27; arm C, n = 14). ABRs (95% confidence interval) for treated bleeds and treated target joint bleeds, respectively, were: arm A, 1.0 (0.53-1.85) and 0.4 (0.18-1.09); arm B, 1.0 (0.50-1.84) and 0.3 (0.12-0.85); arm C, 27.0 (13.29-54.91) and 8.6 (3.15-23.42). The most common adverse event, upper respiratory tract infection, was reported for 14 of 56 (25.0%; emicizumab) and 2 of 14 (14.3%; no prophylaxis) participants. No thrombotic events, thrombotic microangiopathies, or deaths were reported.

Conclusion

Emicizumab 1.5 mg/kg once weekly and 6 mg/kg every 4 weeks demonstrated bleed control in this study population, was well tolerated, and could improve use of prophylaxis in people with hemophilia A.

Off-label use of emicizumab in persons with acquired haemophilia A and von Willebrand disease: A scoping review of the literature

INTRODUCTION

Since the approval of emicizumab, a bispecific, factor VIII-mimetic antibody, for use in persons with congenital haemophilia A in 2018, there have been increasing case reports and case series of off-label use of emicizumab in other bleeding disorders, including acquired haemophilia A (AHA) and von Willebrand disease (VWD).

AIM

We conducted a scoping review on the use of emicizumab in AHA and VWD, focusing on the clinical presentation and outcomes.

METHODS

We conducted a comprehensive search in PubMed, EMBASE and Scopus up to July 15, 2021. The following criteria were applied to the studies identified in the initial search: patients had a diagnosis of AHA or VWD; and the study reported on the clinical outcome of emicizumab use.

RESULTS

Seventeen studies were included in the final review for a total of 41 patients (33 AHA, eight type 3 VWD). The majority of AHA patients and all type 3 VWD patients were started on emicizumab for active/recurrent bleeds. The dosing regimen of emicizumab used varied significantly in AHA patients. All patients had a clinical response to emicizumab use. One AHA patient developed a stroke on emicizumab use in association with concomitant recombinant FVIIa use for surgery. Data on adverse events from emicizumab use were not specifically reported in 24.4% of patients (four AHA, six type 3 VWD).

CONCLUSION

Based on published case reports and case series, emicizumab appears to be an effective haemostatic therapy for AHA and VWD. Larger confirmatory clinical trials are needed to confirm these findings.

Low immunogenicity of emicizumab in persons with haemophilia A

INTRODUCTION

Emicizumab is a humanised, bispecific monoclonal antibody mimicking the cofactor function of activated factor (F)VIII. It is indicated for routine prophylaxis of bleeding episodes in persons with haemophilia A (PwHA) with/without FVIII inhibitors.

AIM

To evaluate the development of anti-emicizumab antibodies and their impact on pharmacokinetics (PK), pharmacodynamics (PD), efficacy and safety in PwHA.

METHODS

Data from seven completed or ongoing phase 3 studies were pooled. The assessment of the immunogenicity profile of emicizumab included anti-drug antibody (ADA) measurement and the association of ADAs with PK, PD, bleeding events, and adverse events.

RESULTS

Of 668 PwHA evaluable for immunogenicity analysis, 34 (5.1%) developed ADAs after exposure to emicizumab. ADAs were transient in 14/34 PwHA (41.2%). ADAs were neutralising in vitro in 18/34 PwHA (52.9%) and associated with decreased emicizumab concentration in 4/668 evaluable PwHA (.6%); of those, one (.1%) discontinued emicizumab due to loss of efficacy. ADAs without decreased exposure did not impact emicizumab efficacy. The proportion of PwHA who had injection-site reactions (ISRs) was higher in ADA-positive PwHA (29.4% vs. 20.8%); however, the safety profile was similar between ADA-positive and ADA-negative PwHA, overall. No cases of anaphylaxis or hypersensitivity were reported in ADA-positive participants.

CONCLUSION

The immunogenicity risk of emicizumab in phase 3 studies was low. ADAs, including in vitro neutralising ADAs, were not associated with a change in safety profile. Routine surveillance is, therefore, not warranted; however, in cases where a loss and/or waning of efficacy are observed, prompt evaluation by a healthcare provider should be sought.

Pharmacokinetics and Associated Efficacy of Emicizumab in Humans: A Systematic Review

INTRODUCTION

Emicizumab is an effective new treatment option for people with hemophilia A (PwHA). The approved dosing regimens are based on body weight, without the necessity for laboratory monitoring. This assumes a clear dose-concentration-response relationship, with acceptable variability due to factors other than body weight. To investigate this assumption, a systematic review on the pharmacokinetics (PK) and associated efficacy of emicizumab in humans was conducted.

METHODS

The EMBASE, Pubmed and CENTRAL databases were systematically searched to November 2020 to identify studies on the PK data of emicizumab in humans. Data on the study, population, PK and efficacy (annualized bleeding rate of treated [joint] bleeds) were extracted and synthesized, and exposure effects modeling was performed using non-linear least squares regression in a maximum effect (Emax) model.

RESULTS

The 15 included studies reported on data for 140 volunteers and 467 PwHA, including children (0 to <12 years) and adolescents and adults (≥12 years), both with and without factor VIII (FVIII) inhibitors. Emicizumab demonstrated dose-linear PK. The interindividual variability of trough concentrations was moderate (32%) and was similar across various subgroups, such as FVIII inhibitor status, age group and dosing interval. The control of bleeds did not further improve above emicizumab concentrations of 30 µg/mL, potentially enabling lower dosing in a substantial proportion of PwHA.

CONCLUSION

This review supports body weight-based dosing, although individualized monitoring of emicizumab concentrations may allow for more cost-effective dosing.

A Model-Based Framework to Inform the Dose Selection and Study Design of Emicizumab for Pediatric Patients With Hemophilia A

Emicizumab is a bispecific antibody mimicking the cofactor function of activated coagulation factor VIII to prevent bleeds in patients with hemophilia A. The dose selection for the first-in-child phase III study of emicizumab was addressed by pediatric pharmacokinetic prediction using an adult/adolescent population pharmacokinetic model developed in phase I-I/II studies. The model was modified to incorporate functions describing the age-dependent increase in body weight (BW) with or without clearance maturation to account for the differences in emicizumab pharmacokinetics between adults/adolescents and children. A minimal dose anticipated to achieve in children the same target efficacious exposure as for adults/adolescents was identified when considering BW and clearance maturation. It was the same BW-based dose as for adults/adolescents and was selected for the starting dose for the pediatric study. Whether considering clearance maturation or not in addition to BW led to uncertainty in the pediatric pharmacokinetic prediction and dose selection, which informed implementation of a dose-adapting scheme in the study design. Exposure matching to adults/adolescents was ultimately achieved in children with the starting dose, indicating that consideration of clearance maturation in addition to BW provided adequate pediatric pharmacokinetic predictions for emicizumab. This pharmacokinetic finding in conjunction with exposure-response information served as a basis for the efficacy demonstrated in children, avoiding a time-consuming process for exploring an optimal pediatric dose of emicizumab. This experience indicates that a model-based framework helped optimize the pediatric dose selection and study design, thereby streamlining the development process with extrapolation, of emicizumab for children.