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In pharmacology, clearance is a pharmacokinetic parameter representing the efficiency of drug elimination. This is the rate of elimination of a substance divided by its concentration. [ 1 ] The parameter also indicates the theoretical volume of plasma from which a substance would be completely removed per unit time.
The elimination rate constant K or K e is a value used in pharmacokinetics to describe the rate at which a drug is removed from the human system. [1] It is often abbreviated K or K e. It is equivalent to the fraction of a substance that is removed per unit time measured at any particular instant and has units of T −1.
Clearance is therefore expressed as the plasma volume totally free of the drug per unit of time, and it is measured in units of volume per units of time. Clearance can be determined on an overall, organism level («systemic clearance») or at an organ level (hepatic clearance, renal clearance etc.). The equation that describes this concept is:
The absorption rate constant K a is a value used in pharmacokinetics to describe the rate at which a drug enters into the system. It is expressed in units of time −1. [1] The K a is related to the absorption half-life (t 1/2a) per the following equation: K a = ln(2) / t 1/2a. [1] K a values can typically only be found in research articles. [2]
In practice, the drug concentration is measured at certain discrete points in time and the trapezoidal rule is used to estimate AUC. In pharmacology, the area under the plot of plasma concentration of a drug versus time after dosage (called “area under the curve” or AUC) gives insight into the extent of exposure to a drug and its clearance ...
Therefore, the urinary and plasma concentrations of sodium must be compared to get an accurate picture of kidney clearance. In clinical use, the fractional excretion of sodium can be calculated as part of the evaluation of acute kidney failure in order to determine if hypovolemia or decreased effective circulating plasma volume is a contributor ...
In pharmacokinetics, a maintenance dose is the maintenance rate [mg/h] of drug administration equal to the rate of elimination at steady state. This is not to be confused with dose regimen, which is a type of drug therapy in which the dose [mg] of a drug is given at a regular dosing interval on a repetitive basis.
It integrates a pharmacokinetic and a pharmacodynamic model component into one set of mathematical expressions that allows the description of the time course of effect intensity in response to administration of a drug dose. PK/PD modeling is related to the field of pharmacometrics.