{"entity":{"id":"radioactive-iodine","kind":"drug","name":"Radioactive iodine (I-131)","aka":[],"tldr":"The original targeted radiotherapy: thyroid cells soak up iodine, so radioactive iodine destroys leftover thyroid tissue and metastases while sparing everything else.","summary":"In use since 1946 for differentiated thyroid cancer; the archetype of theranostics (I-123 or I-131 scans image the same uptake). Roles: remnant ablation after thyroidectomy (now omitted in low-risk disease after ESTIMABL2, IoN, HiLo), adjuvant treatment of intermediate/high-risk disease, and treatment of iodine-avid metastases. Given after TSH stimulation (withdrawal or recombinant TSH). Salivary damage, secondary malignancy at high cumulative doses, and refractoriness in dedifferentiated tumours are the limits.","status":"approved","asOf":"2026-09-07","wikipedia":"https://en.wikipedia.org/wiki/Iodine-131","links":[{"label":"FDA label (DailyMed)","url":"https://dailymed.nlm.nih.gov/dailymed/search.cfm?query=Radioactive%20iodine"}],"tags":[],"related":["i-123","i-131"],"indications":["thyroid"],"sections":[],"technologies":["radioiodine-therapy","radioligand-therapy"],"targets":["sstr2"],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["theranostics","radioiodine-term"],"trials":["hilo","estimabl2","ion-trial"],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"brand":"Sodium iodide I-131","modality":"Radiopharmaceutical (beta/gamma emitter, natural uptake)","mechanism":"Sodium-iodide symporter (NIS) concentrates iodide in thyroid follicular cells; I-131 beta particles (mean path ~0.8 mm) irradiate the cell and neighbours; gamma emission enables imaging.","approvals":[{"region":"US","year":1951,"indication":"Hyperthyroidism and thyroid carcinoma (first radiopharmaceutical approval)"}],"mechanismSteps":["TSH stimulation upregulates the sodium-iodide symporter on thyroid cells","Oral I-131 is absorbed and concentrated in thyroid tissue and iodine-avid metastases","Beta decay deposits radiation within ~1 mm, killing the cells over weeks","Gamma emission allows a post-therapy scan to map uptake"],"dosing":{"route":"Oral capsule or solution","schedule":"1.1 GBq (30 mCi) for remnant ablation (HiLo); 3.7-7.4 GBq for adjuvant or metastatic treatment; low-iodine diet and TSH stimulation beforehand","monitoring":"Post-therapy whole-body scan; thyroglobulin; salivary and marrow function","source":"https://www.thyroid.org/professionals/ata-professional-guidelines/"},"toxicity":[{"event":"Sialadenitis / xerostomia","source":"https://www.thyroid.org/professionals/ata-professional-guidelines/","note":"Dose-dependent; common after repeated high-activity treatment"}],"access":[],"regulatoryEvents":[{"date":"1946","type":"approval","region":"US","note":"First therapeutic use in thyroid cancer (Seidlin); formal approval followed"}]},"route":"/drugs/radioactive-iodine/","neighbours":{"isotope":[{"id":"i-123","kind":"isotope","name":"Iodine-123","route":"/isotopes/i-123/"},{"id":"i-124","kind":"isotope","name":"Iodine-124","route":"/isotopes/i-124/"},{"id":"i-131","kind":"isotope","name":"Iodine-131","route":"/isotopes/i-131/"}],"indication":[{"id":"thyroid-nodule-assessment","kind":"indication","name":"Functional assessment of thyroid nodules","route":"/indications/thyroid-nodule-assessment/"},{"id":"graves-hyperthyroidism","kind":"indication","name":"Graves' disease and hyperthyroidism","route":"/indications/graves-hyperthyroidism/"},{"id":"thyroid","kind":"indication","name":"Thyroid cancer","route":"/indications/thyroid/"}],"technology":[{"id":"radioiodine-therapy","kind":"technology","name":"Radioiodine therapy and whole-body iodine scanning","route":"/technologies/radioiodine-therapy/"},{"id":"radioligand-therapy","kind":"technology","name":"Radioligand therapy (beta emitters)","route":"/technologies/radioligand-therapy/"}],"target":[{"id":"nis-symporter","kind":"target","name":"NIS (sodium-iodide symporter)","route":"/targets/nis-symporter/"},{"id":"sstr2","kind":"target","name":"Somatostatin receptor 2","route":"/targets/sstr2/"}],"term":[{"id":"radioiodine-term","kind":"term","name":"Radioiodine therapy (I-131)","route":"/terms/radioiodine-term/"},{"id":"theranostics","kind":"term","name":"Theranostics","route":"/terms/theranostics/"}],"trial":[{"id":"estimabl2","kind":"trial","name":"ESTIMABL2","route":"/trials/estimabl2/"},{"id":"hilo","kind":"trial","name":"HiLo","route":"/trials/hilo/"},{"id":"ion-trial","kind":"trial","name":"IoN","route":"/trials/ion-trial/"}],"institution":[{"id":"brit","kind":"institution","name":"Board of Radiation and Isotope Technology","route":"/institutions/brit/"}],"company":[{"id":"pdradiopharma","kind":"company","name":"PDRadiopharma","route":"/companies/pdradiopharma/"}]}}