According to the FDA, the following doses are appropriate to take after internal contamination with (or likely internal contamination with) radioactive iodine:
Newborns from birth to 1 month of age should be given 16 mg (¼ of a 65 mg tablet or ¼ mL of solution). This dose is for both nursing and non-nursing newborn infants.
Infants and children between 1 month and 3 years of age should take 32 mg (½ of a 65 mg tablet OR ½ mL of solution). This dose is for both nursing and non-nursing infants and children.
Children between 3 and 18 years of age should take 65 mg (one 65 mg tablet OR 1 mL of solution). Children who are adult size (greater than or equal to 150 pounds) should take the full adult dose, regardless of their age.
Adults should take 130 mg (one 130 mg tablet OR two 65 mg tablets OR two mL of solution).
Women who are breastfeeding should take the adult dose of 130 mg.
Side effects of KI (potassium iodide) may include stomach or gastro-intestinal upset, allergic reactions, rashes, and inflammation of the salivary glands.
When taken as recommended, KI (potassium iodide) can cause rare adverse health effects related to the thyroid gland.
These rare adverse effects are more likely if a person:
Takes a higher than recommended dose of KI
Takes the drug for several days
Has a pre-existing thyroid disease.
Newborn infants (less than 1 month old) who receive more than one dose of KI (potassium iodide) are at risk for developing a condition known as hypothyroidism (thyroid hormone levels that are too low). If not treated, hypothyroidism can cause brain damage.
Infants who receive more than a single dose of KI should have their thyroid hormone levels checked and monitored by a doctor.
Avoid repeat dosing of KI to newborns.