Pharmacology Glossary

The process by which a drug moves from its site of administration into the systemic circulation. The rate and extent of absorption depend on the route of administration, drug formulation, and physiochemical properties of the drug.

A substance that binds to a receptor and activates it to produce a biological response, mimicking the action of the endogenous ligand.

A substance that binds to a receptor without activating it, blocking the action of agonists and preventing the receptor from producing a biological response.

The fraction of an administered drug dose that reaches the systemic circulation in an unchanged form, expressed as a percentage. Intravenous drugs have 100% bioavailability.

The volume of plasma from which a drug is completely removed per unit time, typically expressed in mL/min or L/hr. It reflects the efficiency of the organs of elimination.

A superfamily of heme-containing enzymes located primarily in the liver that catalyze Phase I oxidation reactions in drug metabolism. Major isoforms include CYP3A4, CYP2D6, CYP2C9, and CYP1A2.

The process by which a drug is transported from the systemic circulation to various tissues and body compartments. It is influenced by blood flow, tissue binding, plasma protein binding, and lipid solubility.

A graphical representation of the relationship between drug dose (or concentration) and the magnitude of the pharmacological response, typically sigmoidal in shape.

A change in a drug's effect caused by the concurrent administration of another drug, food, or substance. Interactions may be pharmacokinetic or pharmacodynamic in nature.

The effective dose of a drug that produces 50% of the maximum possible therapeutic response. It is a standard measure of drug potency -- a lower ED50 indicates greater potency.

The process by which a drug or substance increases the synthesis or activity of drug-metabolizing enzymes, leading to faster metabolism and decreased effectiveness of other drugs.

The process by which a drug or substance decreases the activity of drug-metabolizing enzymes, leading to slower metabolism and potentially toxic accumulation of other drugs.

The process of removing a drug and its metabolites from the body, primarily via the kidneys (renal excretion) but also through bile, lungs, sweat, and breast milk.

The initial metabolism of an orally administered drug by intestinal and hepatic enzymes before it reaches the systemic circulation, which can significantly reduce the amount of active drug available.

The time required for the plasma concentration of a drug to decrease by 50%. It is a key determinant of dosing frequency and the time to reach or lose steady-state concentrations.

Any molecule that binds to a specific site on a receptor or other protein. In pharmacology, ligands include drugs, hormones, neurotransmitters, and toxins.

A higher initial dose of a drug administered to rapidly achieve a desired therapeutic plasma concentration before maintenance dosing begins.

The dose of a drug administered at regular intervals to maintain a desired steady-state plasma concentration after the initial loading dose or accumulation period.

A drug that binds to and activates a receptor but produces a submaximal response compared to a full agonist, even at full receptor occupancy. It can act as an antagonist in the presence of a full agonist.

The study of how genetic variations among individuals affect their response to medications, with the goal of tailoring drug therapy based on a patient's genetic profile.

The reversible binding of drugs to proteins in the blood, primarily albumin. Only the unbound (free) fraction of a drug is pharmacologically active and available for distribution, metabolism, and excretion.

A specific protein molecule on or within a cell that a drug or endogenous substance binds to in order to initiate a cellular response. Receptors are the primary targets of pharmacological action.

The condition in which the rate of drug administration equals the rate of drug elimination, resulting in a constant average plasma drug concentration. Achieved after approximately 4-5 half-lives of repeated dosing.

An interaction between two drugs in which the combined effect is greater than the sum of their individual effects. This can enhance therapeutic efficacy but also increase the risk of adverse effects.

A quantitative measure of drug safety expressed as the ratio of the dose that produces toxic effects (TD50) to the dose that produces therapeutic effects (ED50). A high value indicates a wide safety margin.