Indicated in:
- Failure of medical treatment and patient can not stand operation.
- Presence of malignancy.
- Patient above 45 years due to fear of delayed side effect in young age.
- Diagnosis of thyroid function by measuring daily thyroid uptake of ***I132 or I123 ***
131I, emits b and some g radiation which ablates gland. The hyperfunctioning nodules traps and concentrate I131 more than the others nodules. I131 , because of its low penetration remain localized in the diseased nodule. It destroys the thyroid gland by radiation of Beta-rays from I131 with t½ of 5-8 days and without affecting the surrounding nodule.
- Concentrated in thyroid gland - hence no ill effects on rest of body
- Taken orally, physical t1/2 8 days
- Beneficial effect in 1 month, action maximal after 3 months
Side Effects
-
Acute: nausea, vomiting, and pain in the thyroid.
-
Delayed:Â
- Hypothyroidism: Hypothyroidism may be a complication of this therapy, (10 to 20% after one year) requiring eventual thyroid hormone . Up to
- (80% of patients). So, serum FT4 I and TSH levels should be monitored. When this occur, promote replacement with L-thyroxin.
- Metaplasia
- Genetic damage allover the body.
- Leukemia.
Contraindication and Precautions
-
Pregnancy and lactation: because I131 passes the placental barrier and it excreted in milk. It can thus affect the thyroid gland in the foetus. Pregnancy should be deferred for at least 6 months following therapy with radio-active 131
-
Patients under 40 years of age and children, because of the hazard of inducing delayed malignant changes.
-
During thyrotoxic crisis. It is advisable to avoid 131-Rdio-active iodine therapy in patients with active moderate ⇒ severe Graves’ ophthalmopathy.
Preparations and Doses
- I131: mainly used for therapy (half-life = 8 days)
- I132: mainly used for diagnosis (half-life =2-3 hours).
- In therapy use Na I131.
It produces its beneficial effect after 1 - 2 months. In presence of heart disease or large gland treat patient until euthyroid state before giving I131. 6-12 weeks following the radioactive administration, the gland will shrink in size and patient will usually become euthyroid.
Radioactive iodine (131I)
Dose is determined by preliminary uptake test
Adjusted for complete or partial destruction of thyroid with no injury to adjacent tissue
