Description of Sodium Iodide I 123
Sodium iodide is a nutritional supplement for addition to total parenteral nutrition (TPN) solutions. It is primarily indicated to prevent depletion of endogenous iodine stores and related iodine deficiency symptoms. Iodide is the ionized form of iodine, an essential trace element for humans and an integral part of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4). Iodine was first discovered in 1811 and was noted to sublimate into a violet vapor when heated. Because of this, the element is named after the Greek word for violet, ‘iodes’. Deficiency of iodine results in histological changes in thyroid gland and impaired thyroid function, which may cause goiter. Iodine deficiency in early stages of life has been reported to produce cretinism. To combat iodine deficiency and goiter, the United States begin iodizing salt in the 1920s. The typical diet supplies greater than twice the recommended daily amount of 150 mcg. Other dietary sources of iodide include seaweed (kelp, dulse, or sea lettuce), shellfish (clams, oysters, shrimp), and marine fish. Sodium iodide is also present in some multivitamin and mineral combination products. Goitrogens, which interfere with thyroid metabolism, are also present in the typical diet and include nitrates, broccoli, cabbage, brussel sprouts, cassava, and rutabagas.
Mechanism of Action of Sodium Iodide I 123
Iodide is the ionized form of elemental iodine. Iodine is required by the body to produce thyroid hormones. In the thyroid gland, iodide is combined with the amino acid tyrosine to produce thyroxin (T4) and triiodothyronine (T3). These thyroid hormones control the body’s basal metabolic rate and support normal development and growth. Overall thyroid function is modulated by the hypothalamic-pituitary axis through thyroid-releasing hormone and thyroid-stimulating hormone via negative feed back of thyroxine levels in plasma.
Deficiency of iodine (hypothyroidism) results in histological changes in thyroid gland and impaired thyroid function. Symptoms of iodine deficiency include fatigue, cold intolerance, myalgias, heavy or more frequent menstruation, low sex drive, brittle nails, weight gain, alopecia, muscle cramps, depression, constipation, elevated cholesterol, puffy face, dry skin and hair, inability to concentrate, poor memory, and goiter. Iodine deficiency in early stages of life has been reported to produce cretinism (physical and mental retardation). An excess of iodine (hyperthyroidism, Grave’s Disease) may lead to symptoms such as insomnia, heat intolerance, diaphoresis, lighter or less frequent menstruation, hand tremors, rapid pulse, exophthalmos (bug eyes), weight loss, increased appetite, muscle weakness, frequent bowel movements, irritability, nervousness, and goiter.
Pharmacokinetics: Sodium iodide is administered intravenously as a component of total parenteral nutrition (TPN) solutions. In humans, the thyroid gland is estimated to contain 7—8 mg of iodine. Iodide is also taken up by other important organs including salivary glands and gastric mucosa, and, to a lesser extent, choroid plexus, skin, hair, mammary glands, and placenta. The iodine in saliva and gastric mucosal secretions is reabsorbed and recycled. In plasma, circulating iodine is hormonal thyroxine of which 30—70 mcg is protein bound and 0.5 mcg is free thyroxine. Estimated normal plasma inorganic iodide levels are between 0.5 and 1.5 mcg per 100 ml. The kidneys are the major route of excretion. Minor amounts of conjugated thyroid hormones are excreted via the bile.
- Sodium Iodide I 123
- Diagnostic Agent
- Radionuclide thyroid imaging: Adult
- Gastrointestinal: Nausea, Vomiting
- Oral: dispense and preserve capsules in well-closed containers that are adequately shielded
- Oral: capsules can be utilized up to 30 hours after calibration time and date; discard after this time with standard safety procedures
- Oral: waterproof gloves should be worn at all times when handling capsules or container
- Oral Capsule: 100 uCi, 200 uCi
- Radionuclide thyroid imaging: (average patient, 70 kg) for thyroid uptake: 3.7 megabecquerels (100 microcuries) ORALLY
- Radionuclide thyroid imaging: (average patient, 70 kg) for thyroid imaging: 14.8 megabecquerels (400 microcuries) ORALLY
- General Dosage Information: safety and effectiveness have not been established in children
- Oral: readily absorbed