SODIUM IODIDE I 123

Clinical safety rating: caution

Comprehensive clinical and safety monograph for SODIUM IODIDE I 123 (SODIUM IODIDE I 123).

How it works

Sodium iodide I 123 is a radioactive isotope that emits gamma radiation. Following oral or intravenous administration, it is rapidly absorbed and selectively concentrated in the thyroid gland via the sodium-iodide symporter (NIS). The emitted gamma rays allow for imaging of thyroid tissue and detection of abnormal uptake patterns.

What the body does with it

Metabolism	Iodide I 123 is not metabolized; it is excreted primarily unchanged in urine, with small amounts in feces, sweat, and saliva.
Excretion	Primarily renal (90%) as iodide; small amount feces (<5%) and negligible biliary.
Half-life	13.2 hours (physical T1/2); effective T1/2 ~13 hours in euthyroid; prolonged in hypothyroidism.
Protein binding	Negligible (<5%); not significantly bound to serum proteins.
Volume of Distribution	0.2-0.4 L/kg; distributes to thyroid and extracellular fluid, not RBCs.
Bioavailability	Oral: ~95% absorption; IV: 100%.
Onset of Action	Oral: thyroid uptake detectable 2-6 hours; peak activity 24 hours.
Duration of Action	Therapeutic effect (imaging) up to 24-48 hours; residual activity negligible by 7 days.

Classification & Brands

Dosing & administration

Oral: 400-800 μCi (14.8-29.6 MBq) for thyroid uptake studies; 150-300 μCi (5.6-11.1 MBq) for thyroid scan. Administer orally as a single dose.

Dosage form	CAPSULE
Renal impairment	No specific dose adjustment recommended; however, because of renal elimination, caution in severe impairment. GFR <30 mL/min: consider reduced administered activity.
Liver impairment	No specific dose adjustment recommended for Child-Pugh classification.
Pediatric use	Neonates: 2-4 μCi/kg (0.074-0.148 MBq/kg) for uptake study; Infants/Children: 4-8 μCi/kg (0.148-0.296 MBq/kg) for uptake study; dose not to exceed adult dose.
Geriatric use	No specific dose adjustment; consider age-related renal function decline and use lowest effective activity.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for SODIUM IODIDE I 123 (SODIUM IODIDE I 123).

Breastfeeding	I-123 is excreted into breast milk. M/P ratio not established. Radioactivity in milk can be significant; breastfeeding should be interrupted and milk discarded for a period determined by radiation safety guidelines (typically 2-4 weeks post-administration for I-123).
Teratogenic Risk	Radioactive iodine crosses the placenta. Fetal thyroid begins concentrating iodine at 10-12 weeks gestation. I-123 exposure carries risk of fetal thyroid ablation and hypothyroidism, especially after first trimester. Risk is dose-dependent; diagnostic activities used in imaging (e.g., 200-400 μCi) considered lower risk but should be avoided in pregnancy unless benefit clearly outweighs risk.

Warnings & precautions

■ FDA Black Box Warning

None

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to iodide I 123 or any component of the formulation","Pregnancy (absolute contraindication unless diagnostic benefit outweighs risk)"]

Clinical Precautions

Precautions

["Radiation exposure is inherent; risk of carcinogenesis and genetic mutations must be weighed against diagnostic benefits","Pregnancy: Avoid unless clearly necessary; iodine crosses placenta and may cause fetal hypothyroidism","Lactation: Iodine is excreted in breast milk; interrupt breastfeeding for duration of radiation exposure","Hypersensitivity reactions: Rare but possible to contrast agents containing iodine","Thyroid blockade: Use of stable iodine (e.g., SSKI) to reduce thyroid radiation dose in patients with impaired clearance"]

Clinical Tips & Counseling

Drug interactions

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SODIUM IODIDE I 123

Clinical safety rating: caution

Comprehensive clinical and safety monograph for SODIUM IODIDE I 123 (SODIUM IODIDE I 123).

How it works

What the body does with it

Metabolism	Iodide I 123 is not metabolized; it is excreted primarily unchanged in urine, with small amounts in feces, sweat, and saliva.
Excretion	Primarily renal (90%) as iodide; small amount feces (<5%) and negligible biliary.
Half-life	13.2 hours (physical T1/2); effective T1/2 ~13 hours in euthyroid; prolonged in hypothyroidism.
Protein binding	Negligible (<5%); not significantly bound to serum proteins.
Volume of Distribution	0.2-0.4 L/kg; distributes to thyroid and extracellular fluid, not RBCs.
Bioavailability	Oral: ~95% absorption; IV: 100%.
Onset of Action	Oral: thyroid uptake detectable 2-6 hours; peak activity 24 hours.
Duration of Action	Therapeutic effect (imaging) up to 24-48 hours; residual activity negligible by 7 days.

Classification & Brands

Dosing & administration

Oral: 400-800 μCi (14.8-29.6 MBq) for thyroid uptake studies; 150-300 μCi (5.6-11.1 MBq) for thyroid scan. Administer orally as a single dose.

Dosage form	CAPSULE
Renal impairment	No specific dose adjustment recommended; however, because of renal elimination, caution in severe impairment. GFR <30 mL/min: consider reduced administered activity.
Liver impairment	No specific dose adjustment recommended for Child-Pugh classification.
Pediatric use	Neonates: 2-4 μCi/kg (0.074-0.148 MBq/kg) for uptake study; Infants/Children: 4-8 μCi/kg (0.148-0.296 MBq/kg) for uptake study; dose not to exceed adult dose.
Geriatric use	No specific dose adjustment; consider age-related renal function decline and use lowest effective activity.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for SODIUM IODIDE I 123 (SODIUM IODIDE I 123).

Breastfeeding	I-123 is excreted into breast milk. M/P ratio not established. Radioactivity in milk can be significant; breastfeeding should be interrupted and milk discarded for a period determined by radiation safety guidelines (typically 2-4 weeks post-administration for I-123).
Teratogenic Risk	Radioactive iodine crosses the placenta. Fetal thyroid begins concentrating iodine at 10-12 weeks gestation. I-123 exposure carries risk of fetal thyroid ablation and hypothyroidism, especially after first trimester. Risk is dose-dependent; diagnostic activities used in imaging (e.g., 200-400 μCi) considered lower risk but should be avoided in pregnancy unless benefit clearly outweighs risk.

Warnings & precautions

■ FDA Black Box Warning

None

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to iodide I 123 or any component of the formulation","Pregnancy (absolute contraindication unless diagnostic benefit outweighs risk)"]