Definitions - BK

Define Hepatic extraction ratio

The hepatic extraction ratio (EH) indicates the fraction of a drug removed from the blood in one pass through the liver and is determined by factors such as hepatic blood flow, plasma protein binding, and intrinsic clearance.

Define first pass effect

The first pass effect implies that medications with high hepatic extraction are less effective when administered orally, as a significant portion is metabolized before reaching systemic circulation, prompting consideration of alternative administration routes.

Define oral bioavailability.

the fraction of the dose that reaches systemic circulation in chemically unaltered form, calculated as AUC oral dose/AUC iv dose.

Define the extraction ratio.

how effectively a drug is removed from plasma during its passage through an organ, influencing overall clearance depending on hepatic or renal function.

Define the steady-state.

when the rate of drug administration equals the rate of elimination, resulting in a constant plasma drug concentration.

Define clearance.

the volume of plasma from which a drug is completely removed per unit of time, indicating the rate of drug elimination.

Define the elimination rate constant.

a measure of the fraction of a drug dose that is eliminated from the body per unit time, expressed in units such as min⁻¹ or h⁻¹, and it reflects 1st order elimination kinetics.

Define half-life (t1/2).

time taken for the plasma concentration of a drug to fall to half of its initial value, serving as an indicator of drug elimination rate.

Define volume distribution.

the total volume of fluid in which a drug is distributed in the body to achieve a concentration equal to that measured in plasma.

Define loading dose.

initial, usually higher dose of a drug given to quickly reach therapeutic concentrations in the body.

Define salt factor.

the bioavailability of the drug and is critical in accurately calculating the required loading dose based on how much of the drug is effectively available in the system.

Define bioavailability.

the proportion of a drug that reaches systemic circulation unchanged.

Define first-order elimination.

constant fraction of the drug being metabolised per unit of time, the amount eliminated is directly proportional to the amount of the drug in the body

Define zero-order elimination.

constant amount of drug is eliminated per time interval, regardless of the amount in the body.