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Pharmacy & Pharmacology vocabulary · Pharmacokinetics

Half-life

Meaning in pharmacy & pharmacology, with examples

/ˈhæf ˌlaɪf/nounCore term

In pharmacy & pharmacology, half-life means: The time it takes for the amount or concentration of a drug in the blood to fall to half of its starting level.

In Turkish: yarı ömür, yarılanma ömrü, eliminasyon yarı ömrü

How it is used

Written t½ in textbooks. A drug has a short or long half-life, which helps explain how often it is given. With regular dosing, steady state is reached after about four to five half-lives, and most of a drug is gone about four to five half-lives after the last dose. The plural is half-lives.

Example sentences

  1. Because of its long half-life, the drug only needs to be taken once a day.

  2. In kidney failure, the half-life of many drugs increases.

Common collocations

  • long half-life
  • short half-life
  • elimination half-life
  • plasma half-life
  • steady stateThe point during regular dosing when the amount of drug entering the body equals the amount being removed, so blood levels stay within a stable range.
  • clearanceThe volume of blood plasma from which a drug is completely removed per unit of time, usually given in millilitres per minute or litres per hour.
  • eliminationThe removal of a drug from the body through metabolism and excretion, mainly by the kidneys into urine and by the liver into bile.
  • pharmacokineticsThe study of what the body does to a drug: how it is absorbed, distributed, metabolised and eliminated, and how its level in the blood changes over time.

This word in other fields

The same English word can have a different meaning in another field:

More terms: Pharmacokinetics

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This page explains English vocabulary for learners. It is not medical advice.