Pharmacokinetics of Bispecific Antibodies
Key Considerations for PK Assessment
- Free drug concentration at the site of action drives pharmacological effects, making free drug measurements critical for bispecific antibodies that target extracellular antigens 1
- Unlike small molecules, for antibody therapeutics including bispecifics, free drug is typically directly measured as the second part of the free drug hypothesis does not apply 1, 2
- Target-mediated drug disposition (TMDD) significantly affects bispecific antibody clearance, especially at lower doses, necessitating mechanistic PK models that incorporate both free and total measurements 3
Sampling Strategy and Timepoints
- A staggered sampling approach that captures binding kinetics of both receptors is recommended, as they may differ significantly 4
- Precise recording of drug administration and sampling times is essential to ensure accurate PK modeling 4
- Sampling schedules should be designed to capture the full duration of receptor occupancy, particularly for irreversibly binding compounds 4
Laboratory Measurements and Reporting
- Use appropriate laboratory tests for measuring bispecific antibody concentrations and report measurements in standardized units 5
- Include preinfusion samples when the patient receives treatment in the clinic to establish baseline levels 5
- Report activity levels below the limit of quantification (BLQ) rather than discarding this information, as ignoring BLQ data may bias individual estimates 5
PK/PD Modeling Approach
- Integrated PK/PD models that incorporate binding characteristics of both receptors and downstream signaling effects are recommended 4
- Population pharmacokinetic (PopPK) modeling should be used to account for variability in receptor expression and binding across patients 4
- Include pharmacodynamic biomarkers in Phase I trials to confirm target engagement predictions from preclinical models 4