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Absorption half-life 1 h, elimination half-life 12 h. Biological half-life ( elimination half-life , pharmacological half-life ) is the time taken for concentration of a biological substance (such as a medication ) to decrease from its maximum concentration ( C max ) to half of C max in the blood plasma .
In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on.
Pharmacokinetics: . Process of the uptake of drugs by the body, the biotransformation they undergo, the distribution of the drugs and their metabolites in the tissues, and the elimination of the drugs and their metabolites from the body over a period of time.
The drug has an elimination half-life of 4 hours, and an apparent volume of distribution of 10 liters. Pharmacokinetic model of drugs entering a tumor. (A) Schematic illustration of a tumor vessel illustrating loss of smooth muscle cells, local degradation of the extracellular matrix, and increased permeability of the endothelium.
An effective half-life of the drug will involve a decay constant that represents the sum of the biological and physical decay constants, as in the formula: = + With the decay constant it is possible to calculate the effective half-life using the formula:
Flip–flop kinetics, or flip–flop pharmacokinetics, describes an atypical situation in pharmacokinetics where a drug's rate of absorption or the rate at which it enters the bloodstream is slower than its elimination rate. [1] [2] That is, when the k a (absorption constant) is slower than k e (elimination constant).
Distribution is defined as the reversible transfer of a drug between one compartment to another. Some factors affecting drug distribution include regional blood flow rates, molecular size, polarity and binding to serum proteins, forming a complex. Distribution can be a serious problem at some natural barriers like the blood–brain barrier.
Penicillin has a short half-life and is excreted via the kidneys. [61] This means it must be dosed at least four times a day to maintain adequate levels of penicillin in the blood. Early manuals on the use of penicillin, therefore, recommended injections of penicillin as frequently as every three hours, and dosing penicillin has been described ...