Iodopol (Sodium Iodide (131i))

Iodopol is a radioactive iodine preparation used in the management of thyroid disorders.

• Hyperthyroidism (e.g., Graves disease): delivers targeted beta radiation to overactive thyroid cells, decreasing hormone output and achieving disease control.
• Thyroid cancer adjuvant therapy: administered after thyroidectomy to ablate residual thyroid tissue, facilitating postoperative monitoring and reducing recurrence risk.
• Thyroid tissue ablation after thyroidectomy: used to eliminate remaining thyroid cells, improving the effectiveness of subsequent radioactive iodine scans and therapy.

• Sodium Iodide (131I) is taken up by the sodium‑iodide symporter in thyroid follicular cells, where it becomes incorporated into thyroid hormone synthesis pathways. The emitted beta particles cause localized cellular damage, leading to selective destruction of thyroid tissue while sparing surrounding structures. This targeted radiative effect underlies both diagnostic imaging and therapeutic ablation of hyperfunctioning or residual thyroid cells in patients.

Iodopol may be associated with a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Nausea or vomiting: transient gastrointestinal upset occurring shortly after administration.
• Neck pain or tenderness: discomfort in the thyroid region due to radiation‑induced inflammation.
• Sialadenitis (salivary gland inflammation): swelling and pain in the salivary glands, often temporary.
• Taste alteration: temporary changes in taste perception, usually resolving within weeks.
• Mild fever: low‑grade temperature rise that typically subsides without intervention.

Serious or Rare Side Effects

• Bone marrow suppression: reduced blood cell production that can lead to anemia, infection risk, or bleeding.
• Severe hypothyroidism: marked decrease in thyroid hormone levels requiring immediate levothyroxine replacement.
• Radiation thyroiditis: acute inflammation of thyroid tissue causing pain and swelling, may need anti‑inflammatory therapy.

When using Iodopol, specific precautions should be observed to minimize risks and ensure safe handling.

• Pregnancy risk assessment: avoid use unless benefits outweigh potential fetal radiation exposure.
• Breastfeeding contraindication: discontinue breastfeeding for an appropriate period after administration as radioiodine can be secreted in milk.
• Thyroid function monitoring: perform baseline and periodic thyroid hormone tests to detect hypothyroidism or hyperthyroidism.
• Radiation safety measures: maintain distance from others, especially children and pregnant women, for the recommended isolation period.
• Drug interaction review: assess concurrent medications that may affect iodine uptake or increase radiation sensitivity.
• Store at ambient temperature: keep below 25°C in original packaging, protect from moisture and light.

Iodopol can interact with other agents that influence iodine metabolism or radiation effects.

Major Interactions (Avoid)

• Thyroid hormone replacement (levothyroxine): may reduce radioiodine uptake, diminishing therapeutic efficacy.
• Amiodarone: high iodine content can block sodium‑iodide symporter, preventing effective Iodopol action.
• Antithyroid drugs (methimazole, propylthiouracil): interfere with thyroid hormone synthesis and may alter iodine handling.

Moderate Interactions (Monitor Closely)

• Lithium: can increase retention of radioiodine in thyroid tissue, potentially enhancing effect and toxicity.
• Corticosteroids: may reduce inflammatory response to radiation, possibly masking thyroiditis symptoms.
• Contrast agents (iodinated): may saturate iodine pool, decreasing Iodopol uptake if administered shortly before or after.