Iodine-131

(pen-tetate)

💊 Chemical information

Iodo 131.
CAS — 10043-66-0.
ATC — V09CX02 (sodium iodohippurate ( 131 I)); V09FX03 (sodium iodide ( 131 I)); V09IX02 (iobenguane ( 131 I)); V09XA01 (iodine norcholesterol ( 131 I)); V09XA02 (iodocholesterol ( 131 I)); V09XA03 (iodinated human albumin ( 131 I)); V10XA01 (sodium iodide ( 131 I)); V10XA02 (iobenguane ( 131 I)); V10XA53 (iodine tositumomab ( 131 I)).
ATC Vet — QV09CX02 (sodium iodohippurate ( 131 I)); QV09FX03 (sodium iodide ( 131 I)); QV09IX02 (iobenguane ( 131 I)); QV09XA01 (iodine norcholesterol ( 131 I)); QV09XA02 (iodocholesterol ( 131 I)); QV09XA03 (iodinated human albumin ( 131 I)); QV10XA01 (sodium iodide ( 131 I)); QV10XA02 (iobenguane ( 131 I)); QV10XA53 (iodine tositumomab ( 131 I)).
HALF-LIFE. 8.04 days.

💊 Adverse Effects

A percentage of patients treated with iodine-131 for hyperthyroidism become hypothyroid each year, depending on the dose given, and eventually most patients will require thyroid replacement therapy. Hypoparathyroidism has also been reported. Radiation thyroiditis with soreness may develop shortly after treatment. There may be severe and potentially dangerous swelling of the thyroid especially in patients with large goitres and this has on rare occasions produced asphyxiation. Leukaemia and carcinoma of the thyroid have occasionally been reported, particularly in young patients. Retrospective studies have shown an increased incidence of thyroid cancer in adults after iodine-131 treatment for hyperthyroidism. However, the absolute risk of thyroid cancer is small and the underlying thyroid disease may play a role. In the treatment of thyroid carcinoma, the larger doses of radioactive iodine sometimes cause nausea and vomiting a few days after ingestion, which may be due to gastritis as iodine-131 is also concentrated in gastric mucosa. Salivary gland toxicity may also occur. Large doses depress the bone marrow.
1. Ron E, et al. Cancer mortality following treatment for adult hyperthyroidism. JAMA 1998; 280: 347–55
2. Franklyn JA, et al. Cancer incidence and mortality after radioiodine treatment for hyperthyroidism: a population-based cohort study. Lancet 1999; 353: 2111–15
3. Rivkees SA, Cornelius EA. Influence of iodine-131 dose on the outcome of hyperthyroidism in children. Pediatrics 2003; 111: 745–9.

💊 Precautions

The use of sodium iodide (131I) is contra-indicated, even in diagnostic doses, during pregnancy. Sodium iodide (131I) should not be given to patients with large toxic nodular goitres or to patients with severe thyrotoxic heart disease. There is some controversy as to whether radio-iodine therapy exacerbates Graves’ ophthalmopathy. Many drugs have been reported to interfere with thyroid- or other organ-function studies and checks should be made on any treatment the patient might be receiving before any estimations are carried out.

Breast feeding.

The American Academy of Pediatrics has stated1 that temporary cessation of breast feeding is required after exposure to iodine-131 since radioactivity has been reported to be present in breast milk for 2 to 14 days; high doses used for the treatment of thyroid cancer may prolong exposure to the infant.
1. American Academy of Pediatrics. The transfer of drugs and other chemicals into human milk. Pediatrics 2001; 108: 776–89. Correction. ibid.; 1029. Also available at: http://aappolicy.aappublications.org/cgi/content/full/ pediatrics%3b108/3/776 (accessed 01/07/04)

💊 Uses and Administration

Iodine radioisotopes are mainly used in studies of thyroid function and in the treatment of hyperthyroidism and some forms of thyroid carcinoma. Iodine radioisotopes can be incorporated into many compounds including liothyronine and levothyroxine, triglycerides and fatty acids, such as glyceryl trioleate and oleic acid, and proteins, such as iodinated human albumin, with varying degrees of stability and with little or no change in the biological activity of the labelled molecule. It is common practice to saturate the thyroid with non-radioactive iodine when uptake of radiation by the gland is not desired. Sodium iodide (131I) is given orally and by intravenous injection in studies of thyroid function, particularly in measurements of the uptake of iodine by the thyroid, and in thyroid scanning. It is also used in the treatment of hyperthyroidism and in the treatment of malignant neoplasms of the thyroid. Injections containing iobenguane (131I) (m-iodobenzylguanidine (131I)) may be used for the localisation and treatment of phaeochromocytoma and neuroblastoma. Human albumin iodinated with iodine-131 is used in the determination of the blood or plasma volume. Sodium iodohippurate (131I) is used intravenously for renal-function tests and for renal imaging. Rose bengal sodium (131I) has been given intravenously in tests of liver function. Iodinated (131I) norcholesterol (6β-iodomethyl-19-norcholest5(10)-en-3 β-ol (131I)) has been used for adrenal scintigraphy by slow intravenous injection. Various monoclonal antibodies labelled with iodine-131 are used for the detection of malignant neoplasms and some are used for therapeutic purposes, such as iodine (131I) tositumomab for nonHodgkin’s lymphoma.

💊 Preparations

Ph. Eur.: Iobenguane( I) Injection for Diagnostic Use; Iobenguane( I) Injection for Therapeutic Use; Iodinated( I) Norcholesterol Injection; Sodium Iodide( I) Capsules for Diagnostic Use; Sodium Iodide( I) Capsules for Therapeutic Use; Sodium Iodide( I) Solution; Sodium Iodide( I) Solution for Radiolabelling; Sodium Iodohippurate( I) Injection; USP 31: Iobenguane I 131 Injection; Iodinated I 131 Albumin Aggregated Injection; Iodinated I 131 Albumin Injection; Iodohippurate Sodium I 131 Injection; Rose Bengal Sodium I 131 Injection; Sodium Iodide I 131 Capsules; Sodium Iodide I 131 Solution.

Proprietary Preparations

Cz.: Capsion; Curicap; Hippuran; Lipiocis†; Theracap; Neth.: Capsion; Jobenguaan; MIBG; Theracap; Port.: Capsion; Curicap; Theracap; Spain: Curicap; UK: Capsion; Theracap; USA: Bexxar; Hicon; Iodotope.
Published October 31, 2018.