169 General Discussion controlled than the strict Phase I–III trials. Real-world studies (e.g., on remnant material or by retrospective chart review) are currently popular and an excellent approach for evaluating potential overdosing and drug waste. Non-adherence to therapy contributes to variability and can also be assessed in a real-world study. The real-world data can be compared with the literature data to quantify the cost-efficient potential in the target population. For instance, emicizumab’s dose could be halved because concentrations from the real-world study (Chapter 7) were ~60 µg/mL while the effectiveness plateau began already at ~30 µg/mL (Chapter 6). 5. Dosing strategy and measurement A dose strategy can be simple (e.g., ‘halve every dose’ or ‘give only one vial to an individual regardless of body weight’) or straightforward calculated on the back of a napkin (e.g., ‘give a ratio of a dose’), but can also be more complex and then dependent on PKPD modelling simulation. Additionally, dose-PK modelling of multiple costefficient strategies within a virtual population offers a rapid approach to determine the most optimal strategy. Examples of different strategies to consider include entirevial dosing, dose-capping, stratified dosing (e.g., on BMI or age groups) or fixed dosing (i.e., everyone the same dose) in case of a body-weight-based dosing or vice versa (i.e., body-weight dosing if dosing was fixed). Additionally, several initiatives exist to combine a single-use vial for multiple individuals (e.g., when young siblings with haemophilia inject simultaneously) to avoid drug waste. Combining vials should occur in a controlled environment to minimise the risk of contamination and can be included in PK simulations as well. Moreover, the Phase IV experience can yield new user preferences that could be included in PK simulations to explore optimised user convenience. For example, this PK study simulated alternative dosing for emicizumab to minimise the burden of injection pain by extending the dosing intervals and lowering injection volumes [63]. Laboratory measurements of exposure (plasma concentration) or effect (biomarker) can be combined with the dosing strategy or can be mandatory for clinical evaluation (next step). Assays or methods for these measurements are often unavailable due to the novelty of biopharmaceuticals, meaning a method set-up is required. Ligandbinding assays have been the preferred choice for many years, although these have the disadvantages of interference, no multiplex capacity and expensive reagents with long production times [64-66]. The quantification of biopharmaceuticals with LC-MS/MS analysis has the advantages of high sensitivity, speed, resolution, accuracy, reproducibility and multiplex potential, as well as a short development time and small sampling volume. I recommend following the proposed six-step workflow to develop an LC-MS/MS method with bottom-up quantification, entailing the use of a signature peptide, with a multiplex run (Chapter 2). 9
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