Radioactive Iodine

Registered South African indications:

• Hyperthyroidism

Contraindications

• Hypersensitivity to the active ingredient or any of its excipients
• Pregnancy
• Breastfeeding
• Pre-existing vomiting and diarrhoea
• Thyroid malignancies show to have no iodide uptake
• Coadministration with antithyroid medication

Cautions

• Renal impairment
• Elderly
• Cardiac disease
• Hypochloraemia
• Grave's ophthalmopathy
• Children
• Toxic multi-nodular goitre

Forms avail. in SA and covered in this monograph: cap

Hyperthyroidism

• Oral (cap): 150-370 MBq (4-10 millicuries)

Anti-thyroid agents should be withheld for a week before and after the therapeutic dose of iodine-131

Large toxic goitres may not respond adequately with initial doses and may require repeat dosing

Patient at risk of developing or worsening Graves’s ophthalmopathy after iodine-131  should be covered with oral prednisolone

Thyroid cancer

Consult specialist for dosages and regimens

Consult specialist for dosages and regimens 

Pregnancy

• FDA Pregnancy Category X 

Breastfeeding

• Contraindicated

Renal Impairment

• Caution; no dose adjustment recommended

Hepatic Impairment

• No dose adjustment recommended

Elderly

• Caution; no dose adjustment recommended

Central Nervous System Disorders

• Cerebral oedema
• Headache

Cardiovascular Disorders

• Chest pain
• Tachycardia

Respiratory Disorders

• Bronchospasm
• Cough
• Pulmonary fibrosis
• Radiation pneumonitis

Gastrointestinal Disorders

• Nausea and vomiting
• Gastritis
• Salivary gland disease
• Sialadenitis
• Sore throat
• Dry mouth
• Pain on swallowing

Hepatobiliary Disorders

• Hepatic insufficiency

Genitourinary Disorders

• Transient ovarian failure
• Transient inhibition of testicular function

Endocrine and Metabolic Disorders

• Goitre
• Hypothyroidism
• Hyperthyroidism
• Hypoparathyroidism
• Thyroid storm
• Local swelling and tenderness of thyroid

Skin and Subcutaneous Tissue Disorders

• Pruritis
• Skin lesion
• Rash
• Urticaria

Immune, Blood and Lymphatic System Disorders

• Anaemia
• Bone marrow suppression
• Haematological abnormalities
• Leukaemia
• Leukopaenia
• Neoplasm
• Solid tumour
• Thrombocytopaenia
• Hypersensitivity reactions

Sensory Disorders

• Local conjunctivitis
• Epiphora
• Lacrimal duct obstruction
• Dry eyes

• Amiodarone
• Anti-thyroid agents 
• Thyroid products 

Thyroid function

Radioactive iodine acts by damaging the thyroid gland with ionizing radiation. It is thus used therapeutically in hyperthyroidism due to Graves’s disease or toxic single or multi-nodular goitre, and in thyroid cancer for thyroid ablation and treatment of metastatic disease. The effect of the radiation is dose-dependent. When smaller tracer doses of iodine-131 are administered, thyroid function is not disturbed. With properly selected doses, it is possible to destroy the thyroid gland without detectable injury to adjacent tissues.