Lexicon · NucLex for innovators
Pharmacokinetics
Fully specified name: Pharmacokinetics (concept)
The study of how exposure to a substance changes over time through processes such as distribution and elimination.
- Scope note
- State model and measurement assumptions.
- Synonyms
- PK
- Monograph
- Biodistribution and pharmacokinetics (planned; brief only)
- External mappings
- None recorded. In W0 no mapping to SNOMED CT® or any external authority is asserted for this entry. A future mapping record will carry source system, identifier, version, relation type, evidence, author, confidence where meaningful, and review state.
- Formal status
- Editorial entry only. It is not part of any released ontology and a prose edit here changes no formal definition.
Draft. This entry is an unreviewed draft. Its sources have not been checked by a named person and no domain reviewer has approved it. Treat every claim as provisional.
Notes
Pharmacokinetics (PK) is the study of what the body does to a substance: how it is absorbed, distributed, metabolized, and eliminated, and how the resulting exposure changes over time. The counterpart, pharmacodynamics, studies what the substance does to the body. For radiopharmaceuticals the two are linked in an unusual way, because the radiation emitted during the time the agent spends in a tissue is itself the effect of interest.
A pharmacokinetic description is always a model plus data. The data are measurements of concentration or activity in blood, urine, tissue, or images at known times. The model is the set of assumptions used to summarize them: how many compartments, whether transfers are linear, whether the agent is bound or free, and how the curve is extrapolated beyond the last measurement. Quantities such as clearance, volume of distribution, and half-life in tissue are outputs of that model, and they change when the model changes. A reported value without its model and sampling design cannot be reused safely.
Clinical pharmacologists, radiopharmaceutical scientists, and physicists share the vocabulary but emphasize different parts of it. The pharmacologist often works from blood sampling; the physicist from imaging time points to estimate cumulated activity for dosimetry. NucLex records a pharmacokinetic parameter with its model, sampling scheme, population, units, uncertainty, and source so that each community can see what the other measured.