Pharmacokinetic (PK) Studies

The collection of pharmacokinetic (PK) data provides valuable insight into multiple aspects of an investigational product. Sample collection for PK analysis (most commonly blood and urine) in normal healthy volunteers occurs prior to the administration of the study drug in a Phase 1 unit. Samples continue to be collected at designated timepoints post drug administration. In some cases, these studies will require that participants are confined to the facility overnight and for multiple days to enable serial monitoring and improve study compliance.

According to the guidance document Bioequivalence Studies With Pharmacokinetic Endpoints for Drugs Submitted Under an ANDA, it is recommended that between 12 and 18 PK samples be collected after study product administration and should extend through at least three or more terminal elimination half-lives of the drug (1). Per the guidance document Population Pharmacokinetics “As the number of samples per subject decreases, the importance of the timing of PK samples increases (2).” Therefore, it is critical that the samples be obtained as close as possible to the time point relative to the referenced dosing time.

The guidance continues, “We recommend recording the actual clock time when samples are drawn as well as the elapsed time related to drug administration (1).” Therefore, when operationalizing the study, it is imperative to structure the assessments outlined in the protocol to allow for precisely timed sample collection, and to build in sufficient time intervals between subjects.