sodium iodide 131

Action

Incorporated into iodoamino acids in thyroid and deposited in follicular colloid, from where drug is slowly released. Destructive beta particles in follicle act on thyroidal parenchymal cells, minimizing damage to surrounding tissue.

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.

Contraindications

• Vomiting and diarrhea

• Known or suspected pregnancy

Precautions

Use cautiously in:

• hypersensitivity to sulfites (with some products)

• breastfeeding

• children (safety and efficacy not established).

Administration

See 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

Interactions

Drug-drug. Other antithyroid drugs (such as methimazole), iodine, thyroid agents: altered uptake of sodium iodide ¹³¹I

Drug-diagnostic tests. Hemoglobin, platelets, white blood cells: decreased levels

Procedures using contrast media: altered sodium iodide ¹³¹I uptake

Patient monitoring

See Monitor patient to make sure he's following full radiation precautions, including proper body fluid disposal.

See 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.

See Monitor 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.

See Teach patient and significant other how to follow full radiation exposure precautions.

See 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.

See Teach patient to recognize and report signs and symptoms of hypothyroidism and radiation sickness.

See Advise 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.