termsTerm

Pharmacokinetics (PK), half-life and exposure

aka pharmacokinetic, pharmacokinetics, PK/PD, pharmacodynamics, half-life, half life, exposure-response, exposure–response, drug exposure, AUC, Cmax, steady state, steady-state, bioavailability, oral bioavailability, drug-drug interaction, CYP3A4, food effect, therapeutic drug monitoring, TDM, flat dosing, weight-based dosing, body surface area, mg/m², mg/kg

How a drug moves through the body: how much is absorbed, how high the blood level gets, how long it lasts (half-life) and how it is cleared. These numbers decide the dose, the schedule and whether a pill can be taken with food or other medicines.

Antibodies have half-lives of 2-4 weeks and are dosed every 2-6 weeks, often now at flat doses (pembrolizumab 400 mg q6w) rather than by weight; small molecules are dosed daily and interact with CYP3A4 inhibitors, acid suppressants and food; chemotherapy is dosed by body surface area with organ-function adjustments. Exposure-response analyses link drug levels to efficacy and toxicity and underpin Project Optimus's push to find optimal rather than maximal doses; therapeutic drug monitoring is used for busulfan, methotrexate and increasingly for TKIs. Radiopharmaceutical PK determines tumour versus kidney and marrow dose (dosimetry). Poor oral bioavailability has ended more than one promising drug's development.

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Dose reduction, interruption and discontinuation Dosimetry Maximum tolerated dose (MTD)Project Optimus Recommended phase 2 dose (RP2D)Therapeutic index (therapeutic window)