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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.
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:
The elimination half-life of diphenhydramine has not been fully elucidated, but appears to range between 2.4 and 9.3 hours in healthy adults. [6] A 1985 review of antihistamine pharmacokinetics found that the elimination half-life of diphenhydramine ranged between 3.4 and 9.3 hours across five studies, with a median elimination half-life of 4.3 ...
For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the human body. The converse of half-life (in exponential growth) is doubling time. The original term, half-life period, dating to Ernest Rutherford's discovery of the principle in 1907, was shortened to half-life in the early 1950s. [1]
There is an important relationship between clearance, elimination half-life and distribution volume. The elimination rate constant of a drug K e l {\displaystyle K_{el}} is equivalent to total clearance divided by the distribution volume
t 1/2 is the half-life time of the drug, which is the time needed for the plasma drug concentration to drop to its half Therefore, the amount of drug present in the body at time t A t {\displaystyle A_{t}} is;
The drug is bound to albumin with high affinity, while α 1-acid glycoprotein and lipoproteins contribute much less to total plasma protein binding. [7] The unbound or free fraction of levocetirizine has been reported to be 8%. [7] The true volume of distribution of cetirizine is unknown but is estimated to be 0.3 to 0.45 L/kg.
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.