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A biological half-life or elimination half-life is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity.
May 18, 2021 · The elimination half-life of a drug is a pharmacokinetic parameter that is defined as the time it takes for the concentration of the drug in the plasma or...
Jul 14, 2023 · A drug’s half-life is an estimation of the time it takes for the drug’s initial concentration in the body to decrease by half. For example, if a drug’s half-life is 4 hours and the initial concentration is 100 mg, it’s estimated that 50 mg will remain after 4 hours.
For example, the half-life of some drugs, especially those that require both metabolism and excretion, may be remarkably long in older people (see figure ). In fact, physiologic changes with aging affect many aspects of pharmacokinetics (see Pharmacokinetics in Older Adults and Pharmacokinetics in Children).
The half-life of a drug informs its dosing schedule and is especially crucial in situations regarding drug toxicity. Factors that influence the distribution, metabolism, and excretion of a drug can also impact (i.e. increase) the half-life of a drug.
After 4 half-lives the amount of drug (6.25%) is considered to be negligible regarding its therapeutic effects. The half-life of a drug depends on its clearance and volume of distribution. The elimination half-life is considered to be independent of the amount of drug in the body.
Aug 28, 2022 · In pharmacology, the time it takes for a drug to decrease by half its plasma (blood) concentration is called its half-life (t1⁄2). (Specifying that we're talking about biological half-life is key because the half-life is a concept not specific to medicine.
