Moniyot-131 (Sodium Iodide (131i))

Moniyot-131 acts on thyroid tissue and is employed in the following clinical situations:

• Hyperthyroidism: reduces excess thyroid hormone production by destroying overactive thyroid cells.
• Thyroid cancer (ablation): eliminates residual thyroid tissue after thyroidectomy to reduce recurrence risk.
• Diagnostic imaging of thyroid function: provides gamma emission for scintigraphic visualization of thyroid uptake.

• Sodium Iodide (I-131) is a radioactive isotope that mimics stable iodine and is actively taken up by the sodium‑iodide symporter in thyroid follicular cells. Once inside the gland, beta particles emitted by I-131 cause localized cellular damage, leading to tissue ablation, while concurrent gamma photons permit external imaging of thyroid distribution. The selective uptake allows targeted therapy with minimal systemic exposure.

Oral administration of I-131 may be associated with the following adverse reactions.

Common Side Effects

• Nausea or vomiting
• Dry mouth or altered taste
• Transient hypothyroidism
• Neck discomfort or pain
• Mild fatigue

Serious or Rare Side Effects

• Severe hypothyroidism requiring hormone replacement
• Bone marrow suppression leading to cytopenias
• Radiation thyroiditis with painful swelling
• Allergic reactions including rash or anaphylaxis
• Pulmonary fibrosis (rare)

Prior to prescribing Moniyot-131, clinicians should observe these safety considerations:

• Pregnancy: contraindicated (Category X); avoid use in pregnant patients.
• Breastfeeding: not recommended; discontinue breastfeeding during and after treatment.
• Thyroid function monitoring: assess serum TSH and thyroid hormone levels before and after therapy.
• Radiation safety: advise patients on limiting close contact with others, especially children and pregnant women, for a specified period.
• Dosage individualization: determine activity based on patient’s thyroid uptake and clinical status under specialist supervision.
• Store below 25°C: keep in original container, protect from moisture and light.

I-131 can interact with several agents that affect iodine handling or radiation response.

Major Interactions (Avoid)

• Antithyroid drugs (e.g., methimazole, propylthiouracil): reduce iodine uptake and diminish therapeutic effect.
• Lithium: interferes with thyroid hormone release and may increase radioiodine retention.
• Potassium iodide or stable iodine supplements: block I-131 uptake, rendering treatment ineffective.
• Radioprotective agents (e.g., amifostine): may protect thyroid tissue from intended radiation damage.

Moderate Interactions (Monitor Closely)

• Beta‑blockers: may mask symptoms of thyroid hormone changes after therapy.
• Calcium or iron supplements: can modestly affect gastrointestinal absorption of oral I-131.
• ACE inhibitors: monitor renal function as altered clearance may influence systemic exposure.