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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.
Half-life (symbol t ½) is the time required for a quantity (of substance) to reduce to half of its initial value.The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive.
Alternatively, since the radioactive decay contributes to the "physical (i.e. radioactive)" half-life, while the metabolic elimination processes determines the "biological" half-life of the radionuclide, the two act as parallel paths for elimination of the radioactivity, the effective half-life could also be represented by the formula: [1] [2]
The plasma half-life or half life of elimination is the time required to eliminate 50% of the absorbed dose of a drug from an organism. Or put another way, the time that it takes for the plasma concentration to fall by half from its maximum levels.
In pharmacokinetics, steady state refers to the situation where the overall intake of a drug is fairly in dynamic equilibrium with its elimination. In practice, it is generally considered that once regular dosing of a drug is started, steady state is reached after 3 to 5 times its half-life. In steady state and in linear pharmacokinetics, AUC ...
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.
Testosterone undecanoate has a very long elimination half-life and mean residence time when given as a depot intramuscular injection. [27] [7] [8] Its elimination half-life is 20.9 days and its mean residence time is 34.9 days in tea seed oil, while its elimination half-life is 33.9 days and its mean residence time is 36.0 days in castor oil.
The elimination half-life of testosterone in the blood or by intravenous injection is only about 10 minutes. [ 8 ] [ 33 ] Conversely, testosterone and testosterone esters in oil solution or crystalline aqueous suspension administered by intramuscular or subcutaneous injection have much longer half-lives, in the range of days to months, due to ...