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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:
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]
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.
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 chlordiazepoxide is from 5 to 30 hours but has an active benzodiazepine metabolite, nordiazepam, which has a half-life of 36 to 200 hours. [31] The half-life of chlordiazepoxide increases significantly in the elderly, which may result in prolonged action as well as accumulation of the drug during repeated administration.
Nearly half of all 3,100 counties in America have no doctors certified to prescribe buprenorphine by the Substance Abuse and Mental Health Services Administration and the Drug Enforcement Administration, according to a Huffington Post analysis. Hundreds of counties have very few certified doctors.
Sitagliptin was approved by the US Food and Drug Administration (FDA) in October 2006, [30] and is sold under the brand name Januvia. [31] In April 2007, the FDA approved an oral combination of sitagliptin/metformin sold under the brand name Janumet. [ 32 ]