Individual pharmacokinetic assessment is a critical component of tailored prophylaxis for hemophilia patients. Population pharmacokinetics allows using individual sparse data, thus simplifying individual pharmacokinetic studies. Implementing population pharmacokinetics capacity for the hemophilia community is beyond individual reach and requires a system effort.

Among the discussed risk factors for high-titre inhibitor (HRI) development in patients with hemophilia A (HA) are high dose FVIII replacement therapy and use of recombinant FVIII concentrates (rFVIII). The aim of this study was to evaluate the aforementioned risk factors for HRI development in children with hemophilia A ≤2%. About 288 ascertained PUPs (Israel and Germany) were followed after initial HA diagnosis over 200 exposure days. Inhibitor-free survival, hazard ratios (HR), and 95% confidence intervals (CIs) were calculated. Adjustment was performed for factor VIII concentrates, median single dose over the first three months of treatment, first FVIII administration before the age of three months, presence of risk HA gene mutations, "intensive treatment moments" and "year of birth" (proxy for different treatment periods). HRI occurred in 71/288 children (24.7%). In multivariate analysis adjusted for "year of birth", underlying risk gene mutations (HR/CI: 2.37/1.40-3.99), FVIII dose, measured per one IU increase per kgbw (HR/CI: 1.05/1.04-1.07), and first FVIII administration before the age of three months showed a significant impact on HR development. The risk of HRI development was similar for recombinant or plasmatic FVIII products. Children at risk should be treated with carefully calculated lower dose regimens, adapted to individual bleeding situations.

The objective of this scoping review is to summarize the current use of pharmacokinetics for tailoring prophylaxis in hemophilia patients switching between clotting factor products. Patients with hemophilia may require switching of clotting factor concentrates due to a variety of factors, but there have been perceived risks associated with switching, such as inhibitor development or suboptimal protection due to inadequate dosing while titrating treatment. Studies that look at patients switching from one clotting factor concentrate to another are categorized in terms of their primary and/or secondary objectives, notably biosimilarity and comparative pharmacokinetic studies and inhibitor development studies. Research on how best to switch concentrates with respect to dosing regimen are lacking, and currently a trial-and-error approach is used for dosing the new factor concentrate. In the future, studies looking at the predictability of pharmacokinetics (PK) of a new factor concentrate based on individual PK knowledge of the original factor concentrate may offer clinical benefit by providing a safer switching approach and protocol.

Clinical application of population pharmacokinetics (popPK) is of increasing interest to patients with hemophilia, providers, and payers. Routine use of popPK profiles in factor replacement prophylaxis decision making has the potential to maintain or improve efficacy and reduce product consumption.

BAY 94-9027 is an extended-half-life, recombinant factor VIII (rFVIII) product conjugated with a 60-kDa branched polyethylene glycol (PEG) molecule indicated for use in previously treated patients (aged ≥ 12 years) with hemophilia A. This randomized, open-label, two-way crossover study compared the pharmacokinetics (PK) of BAY 94-9027 and rFVIII Fc fusion protein (rFVIIIFc) in patients with hemophilia A. Patients aged 18-65 years with FVIII < 1% and ≥ 150 exposure days to FVIII were randomized to receive intravenous single-dose BAY 94-9027 60 IU/kg followed by rFVIIIFc 60 IU/kg or vice versa, with ≥ 7-day wash-out between doses. FVIII activity was measured by one-stage assay. PK parameters, including area under the curve from time 0 to the last data point (AUClast, primary parameter), half-life, and clearance were calculated. Eighteen patients were randomized and treated. No adverse events were observed. In the analysis set excluding one outlier, geometric mean (coefficient of variation [%CV, 95% confidence interval {CI}]) AUClast was significantly higher for BAY 94-9027 versus rFVIIIFc (2940 [37.8, 2440-3550] IU h/dL versus 2360 [31.8, 2010-2770] IU h/dL, p = 0.0001). A population PK model was developed to simulate time to reach FVIII threshold levels; median time to 1 IU/dL was approximately 13 h longer for BAY 94-9027 versus rFVIIIFc after a single infusion of 60 IU/kg. In conclusion, BAY 94-9027 had a superior PK profile versus rFVIIIFc. ClinicalTrials.gov : NCT03364998.

The total body weight-based dosing strategy currently used in the prophylactic treatment of hemophilia A may not be appropriate for all populations. The assumptions that guide weight-based dosing are not valid in overweight and obese populations, resulting in overdosing and ineffective resource utilization. We explored different weight metrics including lean body weight, ideal body weight, and adjusted body weight to determine an alternative dosing strategy that is both safe and resource-efficient in normal and overweight/obese adult patients. Using a validated population pharmacokinetic model, we simulated a variety of dosing regimens using different doses, weight metrics, and frequencies; we also investigated the implications of assuming various levels of endogenous factor production. Ideal body weight performed the best across all of the regimens explored, maintaining safety while moderating resource consumption for overweight and obese patients.

An open-label, crossover randomized study was performed to compare the pharmacokinetics (PK) of damoctocog alfa pegol and rurioctocog alfa pegol, two recombinant factor VIII (FVIII) products indicated in patients with hemophilia A, both conjugated to polyethylene glycol to reduce clearance and extend time in circulation. Adult patients (N = 18) with severe hemophilia A (FVIII < 1 IU/dL), previously treated with any FVIII product for ≥ 150 exposure days, were randomized to receive a single 50 IU/kg infusion of damoctocog alfa pegol followed by rurioctocog alfa pegol, or vice versa, with ≥ 7-day washout between doses. FVIII activity was measured using the one-stage clotting assay. PK parameters, including area under the curve from time 0 to the last data point (AUC0-tlast, primary parameter), dose-normalized AUC (AUCnorm), and time to threshold, were calculated based on 11 time points between 0.25 and 120 h post-dose and evaluated using a noncompartmental model. Due to differences in batch-specific vial content used for the study, actual administered median doses were 54.3 IU/kg for damoctocog alfa pegol and 61.4 IU/kg for rurioctocog alfa pegol. Based on actual dosing, a significantly higher geometric mean (coefficient of variation [%CV]) AUCnorm was observed for damoctocog alfa pegol (43.8 h kg/dL [44.0]) versus rurioctocog alfa pegol (36.0 h kg/dL [40.1, P < 0.001]). Based on population PK modeling, median time to reach 1 IU/dL was 16 h longer for damoctocog alfa pegol compared with rurioctocog alfa pegol. No adverse events or any immunogenicity signals were observed. Overall, damoctocog alfa pegol had a superior PK profile versus rurioctocog alfa pegol. Trial registration number: NCT04015492 ( ClinicalTrials.gov identifier). Date of registration: July 9, 2019.

Clotting factor concentrates have been the mainstay of severe hemophilia treatment over the last 50 years. Differences in risk of neutralizing antibody (inhibitor) formation according to concentrate used remain clinically relevant.

Existing adult patient pharmacokinetic (PK) data from the published Advate vs Kovaltry PK crossover study were used for this validation study. This data set is appropriate for qualification, given that it has not been previously submitted to Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) and will not have impacted the WAPPS-Hemo models for Kovaltry.

Emicizumab is a bispecific monoclonal antibody developed to address the unmet needs of clotting factor replacement therapy and has become the benchmark for optimal prophylaxis in managing patients with haemophilia A with inhibitors. We describe the emicizumab rollout and pharmacokinetic strategies and their use in paediatric patients.