What it means
A key measure of how long a drug lasts. A drug with a short half-life must be given more often; one with a long half-life can be given once a day or less. It takes about four to five half-lives for a drug to reach a steady level when given regularly, and about the same for it to be mostly cleared after it is stopped. Liver or kidney disease and older age can lengthen it.
For the nurse
Drugs with long half-lives, such as some benzodiazepines, can build up in older adults and cause sleepiness and falls. Watch clients with kidney or liver problems for signs of drug buildup.
At a glance
| Also written | half-lives, half life |
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Related terms
pharmacokinetics
How the body takes in, spreads, changes and gets rid of a drug over time.
pharmacodynamics
The study of what a drug does to the body, and how it does it.
therapeutic range
The span of blood levels of a drug that is high enough to work but low enough to avoid toxic effects.