# Half-life

Source: https://nuclide.cc/terms/half-life/  
Nuclide record `half-life` (Term). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

The time it takes for the amount of a drug in the blood to fall by half. It sets how often a drug must be given: hours to a day for small molecules such as kinase inhibitors, so they are taken daily, and two to four weeks for antibodies, so they are given every three or six weeks.

## Summary

Small molecules are typically cleared by the liver and kidneys within hours to a day, so kinase inhibitors are taken daily; antibodies are protected from breakdown by recycling receptors and persist for two to four weeks, allowing dosing every three or six weeks. Half-life shapes both benefit and harm: a long-lived checkpoint inhibitor keeps working, and keeps causing immune side effects, for months after the last dose, while a radioactive drug's physical half-life (6.6 days for lutetium-177, 10 days for actinium-225) determines how long it irradiates the tumour. Pharmacokinetics is the study of these processes, and matching dose and schedule to them is central to dose optimisation.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: half-lives; half life; plasma half-life; elimination half-life; pharmacokinetics; pharmacokinetic; PK; cleared from the body; drug exposure; peak concentration; Cmax; AUC; steady state; steady-state

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Biological_half-life
- Wikipedia: https://en.wikipedia.org/wiki/Biological_half-life

## Connected records

- terms: [Alpha vs beta emitters](https://nuclide.cc/terms/alpha-vs-beta/), [Biological half-life](https://nuclide.cc/terms/biological-half-life/), [Dosimetry](https://nuclide.cc/terms/dosimetry/), [Effective half-life](https://nuclide.cc/terms/effective-half-life/)
- isotopes: [Actinium-225](https://nuclide.cc/isotopes/ac-225/), [Lutetium-177](https://nuclide.cc/isotopes/lu-177/)
- technologies: [Radioligand therapy (beta emitters)](https://nuclide.cc/technologies/radioligand-therapy/)
- collections: [IAEA nuclear data and isotope databases](https://nuclide.cc/collections/iaea-isotope-databases/)
- indications: [Graves' disease and hyperthyroidism](https://nuclide.cc/indications/graves-hyperthyroidism/)

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