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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:
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.
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]
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;
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
The half-life of methylphenidate is 2–3 hours, depending on the individual. The peak plasma time is achieved at about 2 hours. [ 10 ] Methylphenidate has a low plasma protein binding of 10–33% and a volume of distribution of 2.65 L/kg.
The absorption rate constant K a is a value used in pharmacokinetics to describe the rate at which a drug enters into the system. It is expressed in units of time −1. [1] 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]