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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 of a substance is sometimes expressed as the inverse of the time constant that describes its removal rate from the body divided by its volume of distribution (or total body water). In steady-state, it is defined as the mass generation rate of a substance (which equals the mass removal rate) divided by its concentration in the blood.
where k is the reaction rate constant. Such a decay rate arises from a first-order reaction where the rate of elimination is proportional to the amount of the substance: [39] =. The half-life for this process is [39] = .
k e is the elimination rate constant; The relationship between the elimination rate constant and half-life is given by the following equation: = / Because ln 2 equals 0.693, the half-life is readily calculated from the elimination rate constant.
The rate constants kepr and kb describe extravasation from circulation into the tumor, and intravasation back into the circulation, respectively. The rate constant kel represents clearance by the kidneys, MPS, and any other non-tumor elimination processes, such that when kb = 0, k10 = kepr + kel where kel is the elimination rate constant.
Elimination half-life: The time required for the concentration of the drug to reach half of its original value. 12 h Elimination rate constant: The rate at which a drug is removed from the body.
The Michaelis constant is defined as the concentration of substrate at which the reaction rate is half of . [6] Biochemical reactions involving a single substrate are often assumed to follow Michaelis–Menten kinetics, without regard to the model's underlying assumptions.
k e = Elimination rate constant k a = Absorption rate constant V d = Volume of distribution τ = Dosing interval. C min is also an important parameter in bioavailability and bioequivalence studies, it is part of the pharmacokinetic information recommended for submission of investigational new drug applications. [4]