Pharmacokinetics (PK)

Pharmacokinetics (PK) is the study of how a drug moves through the body over time: its absorption from the site of administration, distribution into tissues and fluids, metabolism (mainly hepatic, through enzymes such as the cytochrome P450 family) and excretion (mainly renal and biliary), collectively known as ADME. Key parameters include bioavailability, maximum concentration (Cmax), time to maximum concentration (Tmax), area under the concentration-time curve (AUC), half-life, clearance and volume of distribution. Pharmacokinetics is paired with pharmacodynamics, the study of the drug's effect, in PK/PD modelling.

PK studies are central to Phase I and to the clinical pharmacology package of a marketing application: first-in-human dose escalation, food-effect, drug-drug interaction, renal and hepatic impairment, bioequivalence for generics and biosimilars, and paediatric extrapolation all rest on PK data. Sparse sampling in later phases is analysed using population PK methods, and regulators accept model-informed approaches under ICH M15 and EMA/FDA guidance.

PK datasets consist of timed drug concentrations for each subject, linked to dosing records, demographics, body weight, organ function and often pharmacogenomic genotypes. They are pseudonymised health data processed by bioanalytical laboratories and pharmacometrics vendors acting as processors, frequently located outside the EEA. Sample shipment, residual sample retention and any future exploratory assays should be covered in the informed consent form, the DPIA and the relevant data processing agreements.