Name of the Thyroid Inhibitor Drugs that Destroy thyroid tissue
- Radioactive iodine 131
Radioactive iodine 131
| Radioactive iodine 131 |
| Availability Iodotope Capsules: radioactivity ranging from 1 to 130 millicuries (mCi)/capsule at time of calibration Sodium Iodide 131I Therapeutic Capsules: radioactivity ranging from 0.75 to 100 mCi/capsule at time of calibration Oral solution: radioactivity ranging from 3.5 to 150 mCi/vial at time of calibration |
| Indications and dosages ➣ Thyroid cancer Adults: Dosage highly individualized. Usual dosage for ablation of normal thyroid tissue is 50 mCi P.O., with subsequent dosages of 100 to 150 mCi P.O. ➣ Hyperthyroidism Adults: 4 to 10 mCi P.O. (usually achieves remission without destroying thyroid). Toxic nodular goiter may require higher dosages. |
Mechanism of Action
Radiopharmaceutical
Thyroid ablation: Destruction of thyroidal tissue is achieved by the beta emission of sodium iodide I-131 and a subsequent thyroid-specific inflammatory response, causing fibrosis and destruction of the thyroid over weeks to many months
Diagnostic: Shows thyroid iodide uptake as a measure of thyroid function
Pharmacokinetics
- Absorption
- Readily absorbed from GI tract after oral administration
- Distribution
- Primarily distributed within the extra-cellular fluid of the body It is trapped by the thyroid
- Thyroid uptake of iodide is usually increased in hyperthyroidism and in goiter with impaired hormone synthesis, decreased in hypothyroidism, and normal-to-decreased in hypothyroidism receiving iodine
- It is also concentrated by the stomach, choroid plexus, and salivary glands
- Protein bound: None
- Metabolism
- Trapped iodide is oxidized to iodine and organically incorporated so rapidly that the iodide trap of the thyroid contains <0.2 % free iodide in comparison to the organically bound iodine
- Elimination
- Half-life: 8.04 days; decays by beta emission and associated gamma emission
- Excretion: Primarily via kidneys; normal range of urinary excretion is 37-75 % of the administered dose, varying with the thyroid and renal function
Contraindications
- Vomiting and diarrhea
- Known or suspected pregnancy
Precautions:
- Hypersensitivity to sulfites (with some products)
- Breastfeeding
- Children (safety and efficacy not established)
Administration
- Don’t administer if you’re pregnant.
- Make sure all antithyroid drugs and thyroid preparations are discontinued 7 days before radioactive iodine therapy begins. Otherwise, consult prescriber about giving thyroid-stimulating hormone for 3 days.
- Instruct patient to fast for 12 hours before therapy starts.
- Know that all doses must be measured by suitable radioactivity calibration system immediately before use.
- For female patient of childbearing age, give drug the week of or week after menstruation.
- Be aware that drug rarely is used to treat hyperthyroidism in patients younger than age 30.
Adverse reactions
- CNS: unusual fatigue
- CV: chest pain, tachycardia
- EENT: pain on swallowing, sore throat
- GI: nausea, vomiting, severe salivary gland inflammation
- Hematologic: anemia, leukopenia, thrombocytopenia, acute leukemia, bone marrow depression, other blood dyscrasias Metabolic: hypothyroidism, transient thyroiditis, acute thyroid crisis
- Respiratory: cough
- Skin: temporary hair thinning, rash, hives, urticaria
- Other: chromosomal abnormalities, neck tenderness and swelling, lymphedema, increase in clinical symptoms, weight gain, radiation sickness, death.
Patient monitoring
- Monitor patient to make sure he’s following full radiation precautions, including proper body fluid disposal.
- If you’re pregnant, don’t provide care to patient who has received this drug.
- If patient has received drug for thyroid cancer, limit contact with him to 30 minutes per shift on first day. Increase as required to 1 hour on second day and longer on subsequent days.
- Monitor thyroxine and thyroid stimulating hormone blood levels, along with CBC with white cell differential.
- Assess fluid intake and output 48 hours after administration. Encourage high fluid intake.
- Watch for signs and symptoms of hypothyroidism, including fatigue, cold intolerance, depression, and sudden weight gain. 2Monitor for bleeding tendency and signs and symptoms of radiation sickness (vomiting, dehydration, skin lesions, and fatigue)
Patient teaching
- Instruct patient to fast for 12 hours before therapy starts and to drink as much fluid as possible for 48 hours after administration. 2Teach patient and significant other how to follow full radiation exposure precautions.
- If patient is receiving drug for thyroid cancer, instruct him to avoid contact with small children. Tell him not to sleep in same room with anyone else for 7 days after receiving dose.
- Teach patient to recognize and report signs and symptoms of hypothyroidism and radiation sickness. 2Advise patient to immediately report unusual bleeding or bruising.
- Tell female patient to inform prescriber if she is pregnant or plans to become pregnant. Caution her not to breastfeed during therapy.
- As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.
REFERENCES
- Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
- McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
- April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
- Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
- Nursebro.com, Search – Nursebro
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