{"entity":{"id":"half-life","kind":"term","name":"Half-life","aka":["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"],"tldr":"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.","asOf":"2026-09-09","wikipedia":"https://en.wikipedia.org/wiki/Biological_half-life","links":[{"label":"Wikipedia","url":"https://en.wikipedia.org/wiki/Biological_half-life"}],"tags":[],"related":["alpha-vs-beta","dosimetry","lu-177","ac-225"],"indications":[],"sections":[],"technologies":["radioligand-therapy"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"Clinic basics"},"route":"/terms/half-life/","neighbours":{"term":[{"id":"alpha-vs-beta","kind":"term","name":"Alpha vs beta emitters","route":"/terms/alpha-vs-beta/"},{"id":"biological-half-life","kind":"term","name":"Biological half-life","route":"/terms/biological-half-life/"},{"id":"dosimetry","kind":"term","name":"Dosimetry","route":"/terms/dosimetry/"},{"id":"effective-half-life","kind":"term","name":"Effective half-life","route":"/terms/effective-half-life/"}],"isotope":[{"id":"ac-225","kind":"isotope","name":"Actinium-225","route":"/isotopes/ac-225/"},{"id":"lu-177","kind":"isotope","name":"Lutetium-177","route":"/isotopes/lu-177/"}],"technology":[{"id":"radioligand-therapy","kind":"technology","name":"Radioligand therapy (beta emitters)","route":"/technologies/radioligand-therapy/"}],"collection":[{"id":"iaea-isotope-databases","kind":"collection","name":"IAEA nuclear data and isotope databases","route":"/collections/iaea-isotope-databases/"}],"indication":[{"id":"graves-hyperthyroidism","kind":"indication","name":"Graves' disease and hyperthyroidism","route":"/indications/graves-hyperthyroidism/"}]}}