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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.
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.
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.
Half-life has units of time, and the elimination rate constant has units of 1/time, e.g., per hour or per day. An equation can be used to forecast the concentration of a compound at any future time when the fractional degration rate and steady state concentration are known:
[17] [194] The apparent elimination half-life of estradiol with transdermal estradiol gel is 36 hours. [194] Once daily application of 1.25 g topical gel containing 0.75 mg estradiol (brand name EstroGel) for 2 weeks was found to produce mean peak estradiol and estrone levels of 46.4 pg/mL and 64.2 pg/mL, respectively. [194]
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 ...
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] This is in contrast to parameters like bioavailability and elimination half-life, which can often be found in drug and pharmacology handbooks. [2]
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.