Pharmacology glossary
Pharmacokinetics basics: absorption, distribution, metabolism, and elimination
Pharmacokinetics describes how a studied compound moves through a biological system over time. ADME is a useful map, while measured concentration-time data and model assumptions determine the actual parameters reported.
Educational content only. Not medical advice.
Absorption and distribution shape early exposure
Absorption describes movement from the administration site into the measured biological system, while distribution describes how material partitions among blood, tissues, and binding compartments. The measured concentration is usually a sample from an accessible matrix, not a direct reading at every target. Molecular size, stability, binding, barriers, and formulation can all affect the observed curve.
Metabolism and elimination remove or transform material
Metabolism converts a parent compound into one or more products that may be inactive, active, or differently detectable. Elimination removes parent or metabolites through biological processes. For peptides, proteolysis, tissue uptake, renal handling, and assay specificity can complicate which molecular species a reported concentration represents.
AUC, peak concentration, clearance, and distribution answer different questions
Area under the concentration-time curve summarizes measured exposure over a defined interval. Peak concentration and time to peak describe other features of the curve. Clearance relates elimination rate to concentration, while apparent volume of distribution is a model quantity connecting amount and measured concentration; it is not a literal anatomical container.
PK parameters are study- and model-specific
Sampling schedule, assay validation, matrix, participant population, route, model structure, and handling of values below quantification can change estimates. A parameter from one formulation, species, or population should not be copied into another context without evidence. This glossary explains how to read reports and does not translate parameters into personal-use instructions.
Evidence limits
- Simple compartmental descriptions can hide nonlinear, target-mediated, or multi-phase behavior.
- Measured matrix concentrations may not equal active concentration at the biological target.
- This page explains study terms and does not calculate or recommend administration amounts.
Sources and further reading
These sources ground the definitions and evidence boundaries on this page. A citation is a route for verification, not an endorsement of a product or personal use.
StatPearls, NCBI Bookshelf
Pharmacokinetics
Authoritative educational synthesis of absorption, distribution, metabolism, elimination, clearance, and exposure measures.
Open sourceU.S. Food and Drug Administration
Bioavailability Studies Submitted in NDAs or INDs: General Considerations
Official guidance on rate and extent of systemic availability, concentration-time measures, and formulation comparisons.
Open sourceU.S. Food and Drug Administration / ICH
Q2(R2) Validation of Analytical Procedures
Official framework for demonstrating that an analytical procedure is fit for its intended purpose.
Open sourceCommon questions
What does ADME stand for?
Absorption, distribution, metabolism, and elimination.
Is volume of distribution a real body volume?
Usually not; it is an apparent model quantity relating amount in the body to measured concentration.
Does higher exposure mean better efficacy?
Not automatically. Exposure-response and safety relationships must be established for the specific compound and outcome.
Continue with context
Keep building your evidence-reading skills
Explore the public PeptideSchool research library for more source-backed methods, glossaries, and evidence maps.