farmakokinetiken

Farmakokinetiken (pharmacokinetics) is the branch of pharmacology that studies the fate of drugs in living organisms. It describes how the body affects a drug through absorption, distribution, metabolism and excretion, collectively known as ADME. The resulting concentration–time profiles are typically measured in plasma or target tissues to understand exposure.

Absorption describes how a drug enters the bloodstream after administration, influenced by route, formulation, gastric pH and first-pass metabolism. Distribution covers movement into tissues, governed by blood flow, tissue binding and the drug's properties; the volume of distribution is a theoretical parameter linking amount of drug to concentration. Metabolism mainly occurs in the liver, often via cytochrome P450 enzymes, producing active or inactive metabolites. Excretion eliminates drugs from the body, primarily via the kidneys or bile.

Key measures include bioavailability (F), half-life (t1/2), clearance (Cl) and the apparent volume of distribution (Vd). These parameters support dosing decisions and the concept of steady state. Pharmacokinetics uses models ranging from noncompartmental analysis to one- and multi-compartment frameworks; physiologically based pharmacokinetic (PBPK) models link anatomy and physiology to drug disposition. PK is often paired with pharmacodynamics (PK/PD) to relate concentrations to effects.

Applications include informing dose, frequency and route; understanding variability due to age, organ function, genetics, disease and drug interactions; and guiding therapeutic drug monitoring and individualized therapy. In drug development, PK data support safety, efficacy assessment and labeling, while population pharmacokinetics studies describe typical values and sources of variability in diverse groups.