Properties : Potassium iodid occurs as colorless or opaque white, cubical crystals, or granulated powder, having a peculiar, faint, iodin-like odor, and a pungent, saline, afterward bitter taste. It is very soluble in water (1:0.1) and soluble in alcohol (1:12).

Incompatibilities: Potassium iodid is incompatible with mineral acids and oxidizing agents and should not be prescribed in solution with alkaloids or alkaloid-containing drugs.

Action and Uses: Potassium iodid is slightly irritating to the gastro-intestinal canal, especially the stomach. After absorption ordinary doses produce no symptoms. It probably undergoes some decomposition with the liberation of iodin. In large or moderate doses, long continued, it frequently produces symptoms of iodism. These are due to irritation of the nasal passages, the bronchi and the skin. The irritation of the nose is shown by coryza, and by pain in the region of the frontal sinus.

There is considerable increase of the bronchial secretions.

On the skin it produces various eruptions, generally of a papular character, which rarely become pustular. Eruption and inflammation of the skin may sometimes be so extensive as to produce constitutional depression.

In iodism there are often symptoms resembling those of exophthalmic goiter—tachycardia, tremor, nervous irritability, etc.

Potassium iodid is regarded as an alterative. It is used as an expectorant to increase secretion in the bronchi. It is of value in subacute and chronic bronchitis. The most remarkable action of iodids is the absorption of gummatous exudates in tertiary syphilis. The iodid does not destroy the spirochetes, but possibly causes the formation of a proteolytic ferment that has a selective action on the round cells composing the gumma. By promoting the absorption of cellular exudates in the walls of the blood-vessels, it exerts a beneficial influence in many cases of arteriosclerosis. There is evidence that the forms of arterial disease which are improved by iodids are of syphilitic origin. A similar absorptive action, almost specific, is seen after administration of large doses of iodids in the granulomatous lesions of actinomycosis, sporotrichosis and blastomycosis.

Potassium iodid is used to promote the elimination of poisons, especially the poisonous metals such as mercury and lead.

Dosage: The dosage varies in non-syphilitic cases from 0.3 to 2 gm. or from 5 to 30 grains, but in cases of syphilis, especially in the tertiary form, much larger doses up to 5 gm. and more may be necessary. It is often advisable to begin with 5 drops of a saturated solution three times a day after meals and increase by 1 drop per day added to each dose. It should not be given on an empty stomach, but with some food, preferably liquid, such as milk. On the occurrence of symptoms of iodism, such as coryza, papular or pustular eruptions, rapid pulse, etc., the remedy should be discontinued and resumed in smaller doses after the disappearance of toxic symptoms.