Determination of concentration-time profiles in cynomolgus monkeys of a therapeutic monoclonal antibody against a soluble target revealed a substantial discrepancy between a generic anti-human IgG capture/detection and target bridging assay with the target bridging assay leading to dose- and time-dependent underquantification of drug concentrations, lack of parallelism and subsequently different pharmacokinetic parameters. In contrast, plasma levels derived from a target capture and an anti-idiotypic antibody bridging assay were in close concordance with the generic assay and demonstrated parallelism with high precision across several dilutions. The results provide a practical attempt to overcome nonparallelism by employing alternative assay formats utilizing tailored assay reagent combinations in order to obtain unbiased pharmacokinetic data.
Keywords: anti-idiotypic antibody bridging assay; generic assay; lack of parallelism; ligand-binding assay; matrix interference; minimum required dilution; nonparallelism; soluble target; target bridging assay; target capture assay.