The Use of Commercial Kits for PK and TK Assays

The majority of kits are ligand-binding assays, for example, ELISAs. There is now consensus within the industry guidelines for validating LBAs for PK methods, as highlighted by the recent conference reports [3,6 9]. 

Assays supporting pharmacokinetic and toxicokinetic studies involve the measurement of the specific test article. Pharmacokinetic and toxicokinetic measurements are an important part of the drug development process since it is important to correlate the levels of drug in biological fluid with the dose. 

Kit methods in general are only available for new drugs or NCEs if the compound itself is a form of an endogenous compound, for example, GM-CSF, erythropoietin, 

It is important to assess the relative differences between the test article and the kit standards. In most cases, there will be differences between the provided calibration standards and the test article. In this case it is advisable to replace the calibration standards with standards prepared from the test article and, in the authors opinion, this is advisable in the majority of cases. 

If the decision is made to use the kit standards, then the assay should be controlled using quality controls prepared from suitable test article material. As in the case of the calibration standards, it is unlikely that sufficient quality controls will be provided in the kit to support a PK assay in terms of both number and volume. 

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