Can I take Sodium Iodide I 131 if I am pregnant?

No, Sodium Iodide I 131 is strictly forbidden during pregnancy because it can cause permanent thyroid damage to the unborn baby.

Should I stop breastfeeding before my Sodium Iodide I 131 test?

Yes, you should stop breastfeeding after receiving Sodium Iodide I 131 to prevent the baby from getting radiation through your milk.

What side effects are common with Sodium Iodide I 131?

Common side effects include nausea, vomiting, diarrhea, itching, rash, and hives.

How does food affect my Sodium Iodide I 131 test?

You should follow a low-iodine diet for two weeks before the test and fast for at least 2 hours before and after taking the capsule.

Can Sodium Iodide I 131 cause an allergic reaction?

Yes, some people may experience hypersensitivity reactions, including anaphylaxis, particularly if they have a sulfite allergy.

Why do I need to drink lots of water after taking Sodium Iodide I 131?

Drinking plenty of fluids and urinating frequently helps your body get rid of the radioactive material more quickly.

Does Sodium Iodide I 131 increase cancer risk?

Because it is radioactive, it contributes to long-term radiation exposure, which is linked to an increased risk of cancer.

What should I do if I accidentally take too much Sodium Iodide I 131?

Medical professionals will monitor for thyroid suppression and may use blocking agents while encouraging hydration and frequent urination.

Sodium Iodide | CAS 7681-82-5 | FVAUCKIRQBBSSJ

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Radioactive Diagnostic Agent

Sodium Iodide I 131 is a radioactive medicine used by adults to check how well the thyroid is working or to take pictures of the thyroid gland. Because it is radioactive, it must be handled with care to limit radiation exposure.

How it worksIodine is naturally pulled into the thyroid cells. This medicine uses a radioactive version of iodine (I-131) so that doctors can track its movement to see how the thyroid is functioning.

Brand names:Sodium Iodide I 131 Diagnostic

Used for

Checking thyroid function using a radioactive iodine uptake testImaging the thyroid gland (scintigraphy)

Conditions

Thyroid function determinationThyroid imaging

Class

Diagnostic AidRadioactive AgentSupplementRadioactive Diagnostic AgentEndocrine system

How to take

FormsOral capsule

RoutesOral

The dose depends on whether the doctor is testing thyroid function or taking images. For thyroid function tests, the dose is 0.185 to 1.1 MBq. For thyroid imaging, the dose is 1.85 to 3.70 MBq. Always follow the specific instructions provided by your healthcare provider.

You should fast for at least 2 hours before and 2 hours after taking the capsule. It is also important to drink plenty of fluids before and after the procedure and to urinate frequently to help clear the radiation from your body.

Key warnings

·Sodium Iodide I 131 can cause permanent and severe thyroid problems in a newborn if taken during pregnancy.
·This medicine is radioactive and contributes to long-term radiation exposure, which may increase cancer risk.
·Taking certain foods or other medicines (like thyroid hormones or contrast dyes) before the test can make the results inaccurate.
·People with allergies to sulfites should be cautious, as some capsule ingredients may cause a reaction.

Do not use if

·Pregnancy

Side effects

Common

NauseaVomitingDiarrheaItchingRashHivesRedness of the skinLocal swelling in the thyroid area

Serious

·Severe allergic reactions (anaphylaxis)
·Severe thyroid problems in newborns (if exposed during pregnancy)

Seek help if

·Anaphylaxis
·Severe allergic reactions

Interactions

·Thyroid hormones (thyroxine, etc.)
·Anti-thyroid drugs (methimazole, etc.)
·Multivitamins containing iodine
·Iodine-rich foods (seaweed, seafood, dairy, egg yolks, iodized salt)
·Radiographic contrast agents (imaging dyes)
·Amiodarone

FoodA low-iodine diet is often required for two weeks before the test, and you should fast for 2 hours before and after taking the capsule.

Special populations

PregnancySodium Iodide I 131 should not be used during pregnancy. The radiation can cross the placenta and cause severe, permanent thyroid issues in the baby, including issues with mental development and bone growth.

BreastfeedingWomen should stop breastfeeding after taking Sodium Iodide I 131 because the radioactive iodine will pass into breast milk and can affect the baby's thyroid.

PediatricThe safety and effectiveness of Sodium Iodide I 131 in children have not been established. Children's thyroid glands may be more sensitive to the effects of radiation.

GeriatricNo specific differences in safety were found in older adults, but elderly patients may have decreased kidney function, which can lead to higher radiation exposure.

Talk to your doctor

Monitor

·Thyroid function
·Signs of allergic reaction
·Radiation exposure levels

Questions to ask

·Should I stop taking my thyroid medication before the test?
·Do I need to follow a low-iodine diet?
·How long should I wait before breastfeeding again?
·What precautions should I take to protect my family from radiation exposure?

Pharmacokinetics

Onset90% of the dose is absorbed within the first 60 minutes.

Half-lifeThe physical half-life of Iodine I 131 is 8.04 days. The effective half-life in the thyroid ranges from 80 to 90 hours.

Bioavailability90% absorption after oral administration.

MetabolismIodide is oxidized by thyroid peroxidase to iodinium, which then binds to thyroglobulin.

ExcretionExcreted in urine (37% to 75%) and feces (about 10%).

Practical

OverdoseIn case of overdose, doctors may monitor for thyroid suppression and may give a thyroid-blocking medicine. Staying hydrated and urinating frequently is recommended to help remove the radiation.

StorageMaintain adequate shielding during the life of the product.

Ingredients

Allergens

sulfite

Inactive

disodium edetate dihydrate USPsodium thiosulfate pentahydrate USPdibasic sodium phosphate anhydrous USPgelatin

Educational summary derived from FDA labeling, AI-assisted. Not medical advice — consult a healthcare professional. Updated 2026-04-26.