What is Sodium Iodide I-131: Uses, Dosage, Side Effects and More

Sodium Iodide I-131 is a radioactive form of iodine used as medicine to treat certain thyroid conditions. Your thyroid gland naturally absorbs iodine, so when you take this radioactive version, it travels directly to your thyroid where it can destroy overactive thyroid cells or cancerous tissue. This targeted approach makes it an effective treatment for specific thyroid problems that other medications might not handle as well.

What is Sodium Iodide I-131?

Sodium Iodide I-131 is radioactive iodine that comes as a liquid or capsule you swallow. The "I-131" refers to a specific type of iodine that gives off controlled amounts of radiation. This radiation is much different from what you might think of with nuclear accidents - it's carefully measured and designed to work only in your thyroid gland.

The medication works because your thyroid has a unique ability to collect and store iodine from your bloodstream. When you take I-131, your thyroid pulls it in just like regular iodine, but the radioactive version delivers targeted treatment right where it's needed. The radiation gradually decreases over time, typically becoming much weaker within a few weeks.

What is Sodium Iodide I-131 Used For?

Doctors prescribe I-131 primarily for two main thyroid conditions: hyperthyroidism and thyroid cancer. For hyperthyroidism, it helps calm down an overactive thyroid that's producing too much hormone. For thyroid cancer, it can destroy any remaining cancer cells after surgery.

If you have hyperthyroidism, your thyroid might be working overtime due to conditions like Graves' disease or toxic multinodular goiter. The radioactive iodine essentially "burns out" the overactive thyroid cells, bringing your hormone levels back to normal. This treatment is often recommended when medications aren't controlling your symptoms well enough.

For thyroid cancer patients, I-131 serves as an additional safety measure after thyroid surgery. Even when surgeons remove all visible cancer, microscopic cells might remain. The radioactive iodine can find and destroy these hidden cancer cells throughout your body, reducing the chance of cancer returning.

How Does Sodium Iodide I-131 Work?

I-131 is considered a strong and highly effective medication for thyroid conditions. It works by delivering radiation directly to thyroid cells, which are uniquely designed to absorb iodine. This targeted approach means the radiation affects mainly your thyroid, with minimal impact on other parts of your body.

Once you swallow the medication, it enters your bloodstream and travels to your thyroid gland. Your thyroid cells eagerly absorb the radioactive iodine, thinking it's regular iodine they need for hormone production. Over the following days and weeks, the radiation gradually damages or destroys the targeted thyroid cells.

The process is gradual and controlled. You won't feel the radiation working, and the effects build up slowly over time. For hyperthyroidism, you might notice your symptoms improving over several weeks to months. For cancer treatment, the goal is eliminating any remaining cancer cells that regular treatments might have missed.

How Should I Take Sodium Iodide I-131?

You'll take I-131 on an empty stomach, typically after fasting for several hours. Your doctor will give you specific instructions about when to stop eating and drinking before your treatment. Most people need to avoid food for at least 2 hours before taking the medication and for 1-2 hours afterward.

The medication comes as either a liquid you drink or a capsule you swallow with water. If it's liquid, you might taste a slight metallic flavor, which is normal. Some treatment centers will give you a mint or gum afterward to help with any aftertaste. The whole process of taking the medication usually takes just a few minutes.

Your healthcare team will also give you detailed instructions about special precautions to take for several days after treatment. These might include sleeping alone, using separate bathrooms when possible, and washing your clothes separately. These precautions help protect family members from unnecessary radiation exposure while your body processes the medication.

How Long Should I Take Sodium Iodide I-131 For?

Most people take I-131 as a single dose, not as an ongoing medication. For hyperthyroidism, one treatment is often enough to bring your thyroid function back to normal. You'll have follow-up appointments to monitor your progress and see if additional treatment is needed.

If you're being treated for thyroid cancer, you might need multiple doses spaced several months apart. Your doctor will determine this based on your specific situation, including the type and stage of cancer you had. Some people need just one dose, while others might need two or three treatments over the course of a year or more.

The effects of each dose continue working for weeks to months after you take it. Your doctor will track your progress through blood tests and scans to see how well the treatment is working. Based on these results, they'll decide whether you need additional doses or if your treatment is complete.

What Are the Side Effects of Sodium Iodide I-131?

Most people experience relatively mild side effects from I-131, though everyone's experience is different. The most common side effects happen because the radiation affects your thyroid and sometimes your salivary glands, which also absorb small amounts of iodine.

Here are the side effects you might notice in the first few days to weeks after treatment:

• Neck tenderness or swelling where your thyroid is located
• Dry mouth or changes in taste that can last several weeks
• Mild nausea, especially on the day of treatment
• Fatigue as your body adjusts to changing hormone levels
• Temporary worsening of hyperthyroid symptoms before improvement begins

These common side effects are usually manageable and improve on their own as your body processes the medication.

Less common but more serious side effects can include swelling in your neck that affects swallowing, persistent nausea and vomiting, or signs of very low thyroid function like extreme fatigue and depression. If you experience severe neck swelling, difficulty swallowing, or persistent vomiting, contact your doctor right away.

In rare cases, some people develop problems with their salivary glands that can cause long-term dry mouth or taste changes. There's also a small risk of developing other cancers many years later, though this risk is generally considered very low compared to the benefits of treating your thyroid condition.

Who Should Not Take Sodium Iodide I-131?

I-131 is not safe for pregnant women because radiation can harm a developing baby's thyroid gland. If you're pregnant or think you might be, tell your doctor immediately. You'll need a pregnancy test before treatment, and you should avoid becoming pregnant for several months after treatment.

Breastfeeding mothers also cannot take I-131 because the radioactive iodine passes into breast milk. If you're breastfeeding, you'll need to stop completely before treatment and wait several months before resuming, depending on your doctor's recommendations.

People with certain medical conditions need special consideration before taking I-131. If you have severe heart problems, uncontrolled thyroid hormone levels, or certain types of eye problems related to thyroid disease, your doctor might want to stabilize these conditions first. Some people with kidney problems might also need dose adjustments.

Young children typically don't receive I-131 unless absolutely necessary, as their developing bodies are more sensitive to radiation. Doctors usually try other treatments first in pediatric patients.

Sodium Iodide I-131 Brand Names

I-131 is available under several brand names, including Hicon and Sodium Iodide I-131. However, many hospitals and nuclear medicine departments prepare their own radioactive iodine solutions, so you might not see a specific brand name on your treatment.

The medication itself is the same regardless of the brand or preparation method. What matters most is that it's prepared by qualified professionals in a licensed nuclear medicine facility. Your treatment team will ensure you receive the correct dose and type of radioactive iodine for your specific condition.

Sodium Iodide I-131 Alternatives

For hyperthyroidism, alternatives to I-131 include anti-thyroid medications like methimazole or propylthiouracil, and surgical removal of part or all of your thyroid. Anti-thyroid medications work more slowly and need to be taken daily, but they don't involve radiation. Surgery provides immediate results but requires general anesthesia and has surgical risks.

For thyroid cancer, alternatives depend on your specific type and stage of cancer. These might include additional surgery, external radiation therapy, or newer targeted therapy medications. Some people with very low-risk thyroid cancers might not need any additional treatment beyond surgery.

Your doctor will help you weigh the benefits and risks of each option based on your age, overall health, the severity of your condition, and your personal preferences. I-131 is often recommended because it's highly effective and typically requires fewer ongoing treatments than other options.

Is Sodium Iodide I-131 Better Than Methimazole?

I-131 and methimazole work differently and are better for different situations. I-131 is often more effective for long-term control of hyperthyroidism because it provides a permanent solution. Most people who receive I-131 don't need ongoing daily medications for their hyperthyroidism.

Methimazole is an anti-thyroid medication you take daily to block hormone production. It works more gradually and reversibly, meaning your thyroid function can return to normal if you stop taking it. This makes methimazole a good choice for people who want to avoid radiation or who have milder hyperthyroidism.

I-131 is typically recommended when methimazole hasn't worked well enough, when you've had side effects from anti-thyroid medications, or when you prefer a one-time treatment over daily medications. The choice between them depends on your specific situation, age, and preferences.