131I-Sodium Iodide (131I-NaI) - Dr. Abdolghafar Abolhosseini

Description

¹³¹I-Sodium Iodide (¹³¹I-NaI) is a cornerstone diagnostic and therapeutic radiopharmaceutical widely used for thyroid-related diseases, including thyroid carcinomas. It is typically administered as swallowable gelatin capsules, although liquid and injectable forms are also available. Introduced as the first radiotherapeutic in humans in 1941, it became a standard treatment by the 1950s.

Historical Significance

First Use: 1941
Standardized Therapy: Early 1950s

Clinical Applications

Diagnostic Use

¹³¹I-Sodium Iodide is effective in diagnosing thyroid-related conditions such as:

Thyroid cancer metastases localization
Thyroid dysfunction: Includes hyperthyroidism and hypothyroidism

Typical diagnostic doses range from 0.3 to 2 mCi.

Therapeutic Use

At higher doses, ¹³¹I-NaI is used for treating:

Thyroid carcinoma and its metastases
Nodular goiter
Hyperthyroidism (Graves’ disease, Plummer’s disease)

Therapeutic doses can reach up to 150 mCi.

Availability and Pricing

¹³¹I-Sodium Iodide is a widely available radiopharmaceutical supplied by many manufacturers. While forms and dosages vary, capsules and liquid solutions are the most common.

Key Suppliers and Products:

Bracco: Iodotope (capsules, discontinued)
GE Healthcare: Theracap131 (EU MA 2009)
IBA Molecular (Curium): Capsion® (capsules), injectable solution
Mallinckrodt: Sodium Iodide (capsules and injectable)
Fuji Film, Pars Isotope, POLATOM

Pricing:

Capsules (2020, USA): Approximately $40/mCi
Pharmaceutical grade iodine (US & EU): $40–$120/mCi

Competitive Landscape

For thyroid imaging and treatment, iodine isotopes dominate the market due to their specificity for thyroid cells. Key alternatives include ¹²³I, ¹²⁴I, and ¹²⁵I, but ¹³¹I-Sodium Iodide remains unmatched for therapeutic purposes.

Notable Competitors

Generic forms offered by various manufacturers
Newly introduced formulations, such as Iodine MAX by International Isotope Inc, approved in 2016

Comments and Insights

Mechanism of Action
¹³¹I-Sodium Iodide exploits the thyroid’s natural affinity for iodine, allowing it to concentrate radioactivity specifically in thyroid tissues, including cancer cells and metastases. This selective targeting makes it highly effective for both imaging and treatment.
Precautions
The administration of non-thyroid-specific radio-iodinated compounds may release free iodine, potentially impacting thyroid function. To mitigate this, thyroid blockade with non-radioactive iodine is required before treatment.
Emerging Research

Astatine-labeled molecules, due to similarities in chemical behavior, could offer future applications in thyroid cancer treatments.
Thyroid uptake of bromine and astatine salts warrants further exploration in therapeutic contexts.

Challenges in Japan
A lack of shielded rooms has resulted in waiting times of up to 18 months for iodine radiotherapy in Japan, contributing to a 4-5x increase in thyroid cancer mortality rates.