Pharmacology Dictionary

LD50 = medium lethal dose – the dose of a substance at which 50% of the individuals in the tested sample die within a certain time frame. The LD50 of a substance serves as the indicator of its acute toxicity. An LD50 is generally measured in mg/kg and has to be accompanied by: substance, test animal and route of administration (e.g. intravenous LD50 of morphine in rats).

t½ = half-life – in pharmacology, the half-life of a substance is the time required for an organism to eliminate 50% of the substance, through excretion and/or metabolism. The half-life of a substance in an organism generally depends on its concentration, as large amounts of a substance may saturate certain pathways of elimination (e.g. a particular enzyme), reaching the limit of the elimination rate.

Bioavailability (F) = the percentage of an administered dose of a substance that reaches the bloodstream unchanged. Bioavailability depends on substance, dose, route of administration, and individual differences. For example, oral bioavailability of a certain substance is limited by absorption in the gastrointestinal tract and by first-pass metabolism (breakdown before entering bloodstream).

Enzyme = organism-produced protein that acts as a catalyst of chemical reactions ("enzymatic reactions"), i.e. accelerates reactions without being itself modified. Enzymes bind to specific "substrates" and chemically transform them into "products." Enzymes play crucial roles in all living organisms.

tmax = time from administration to maximum plasma concentrations of administered substance (Cmax).

AUC = area under curve. Blasma levels of an administered substance are recorded from administration until they are negligible, and displayed in a concentration-versus-time plot. AUC is the area under the curve of this plot and is used to interpret total uptake of the substance (bioavailability). AUC has to be accompanied by substance, dose, route of administration, and the time frame in which concentrations were measured (e.g. AUC of 200 mg oral tramadol, 0 to 7h).

Ki = binding affinity of a substance to a certain protein (receptor, transporter, ion channel, enzyme, etc).

mg/kg = milligrams per kilogram of body weight. Is a more accurate calculation of dosage than mass only.