Iodide (large dose) is used for thyroid storm (crisis) and in preparation for thyroidectomy because it rapidly benefits the patient by reducing hormone release and renders surgery easier and safer (above).
Potassium iodide in doses of 60 mg orally 8-hourly (longer intervals allow some escape from the iodide effect) produces some effect in 1-2 days, maximal after 10-14 days, after which the benefit declines as the thyroid adapts. A similar dose is used for 3 days to cover administration of some 131- or 123-Iodine containing isotopes, for instance metaiodobenzyl-guanidine (MIBG) (see p. 492).
Iodine therapy maximises iodide stores in the thyroid, which delays response to thionamides. Prophylactic iodide (1 part in 100 000 parts) may be added to the salt, water or bread where goitre is endemic.
In economically deprived communities a method of prophylaxis is to inject iodised oil i.m. every 3-5 years; given early enough to women, this prevents endemic cretinism; but occasional hyperthyroidism occurs (see Autonomous adenoma, above).
As an antiseptic for use on the skin, providone-iodine (a complex of iodine with a sustained-release carrier, povidone or polyvinylpyrrolidone) is used. It can be applied repeatedly and used as a surgical scrub.
Bronchial secretions. Iodide is concentrated in bronchial and salivary secretions. It acts as an expectorant (see Cough, p. 550).
Organic compounds containing iodine are used as contrast media in radiology. It is essential to ask patients specifically whether they are allergic to iodine before they are used. An i.v. test dose ought to be given half an hour before the full i.v. dose if there is history of any allergy. Despite this, severe anaphylaxis, even deaths, occur every year in busy radiology departments, and iodine containing contrast media are being superseded by so-called nonionic preparations.2
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