This section is from the "A Practical Treatise On Materia Medica And Therapeutics" book, by Roberts Bartholow. Also available from Amazon: A Practical Treatise On Materia Medica And Therapeutics
When the prolonged administration of iodine or iodides becomes necessary, certain precautions must be observed to prevent the development of iodism. Especially will such precautions be necessary when massive doses of iodides are administered through many months and years in cases of arterio-sclerosis. Prof. Sée maintains that by occasional intermissions, and the use of eliminants at such times, iodism may be prevented.
Ehrlich, and subsequently Krönig, have ascertained that sulphanilic acid has the power to prevent or arrest iodism. The action is a chemical one, and is explained thus: the phenomena of iodism are due to-the presence of free iodine, and this agent is separated from its combinations by the nitrates in the presence of a weak acid. As sulphanilic acid has a strong affinity for nitric acid, the raction which frees iodine is prevented.
Atropine is quite effective as a remedy for iodism, by arresting the morbid action taking place on the mucous surface, where the recombination of iodine is taking place (Binz). Some of the rashes, hydroa, etc., which belong to iodism, are also removed by atropine. The acne the gastric disturbances, and the depression of the vital powers, are to some extent favorably affected by arsenic, and hence, if there be no contraindications, it can be given in the same prescription with the iodides. It is iodine, rather than the iodides, when given in large quantity, that produces the state termed iodism. The quantity which will set up this state of irritation in one subject will affect another but slightly, if at all; in other words, the susceptibility to the iodine impression varies greatly in different individuals. Iodism is manifested by general malaise and rise of temperature, frontal headache, coryza, lachryma-tion, and sometimes inflammatory swelling of the eyelids, a bittter saline taste in the mouth, soreness of the throat, hoarseness, and difficulty of swallowing—phenomena strikingly similar to summer catarrh. Indeed, patients who experience these sensations for the first time, sup pose them to be an acute catarrh. Usually the symptoms of iodism subside, notwithstanding the dose which caused them may still be taken, or, as it may be expressed, a "tolerance" is established. The quantity which at one time may have caused violent iodism will not necessarily again do so, although a considerable interval may have elapsed. Indeed, it is sometimes difficult to induce iodism in those who have become habituated to the use of the iodides in considerable medicinal doses.
An eruption of acne, especially on the face, shoulders, and thighs, is a very common result of the internal use of the iodides; hydroa on the face and forehead is an occasional consequence, but eczema is more frequent, yet less so than acne, which is usual.
Wasting of the mammae and of the testes has never been observed by the author, although he has used the largest doses of the iodides, for long periods. There is no doubt about their antaphrodisiac effects, and it has seemed to the author that permanent loss of sexual power has resulted from their long-continued use.
When it is desirable to avoid iodism, large draughts of water should be taken during a course of the iodides. As Rosenthal has shown, large dilution of the salt hastens elimination, and thus prevents the more severe effects of iodism.
Benedict has experimentally studied the effects of iodine and of iodide of potassium on the nervous system. His observations, made on frogs, demonstrated that these agents caused paralysis of the heart and of the respiration. Schule reports a case in which such symptoms were induced by injecting the sac of a spina bifida with tincture of iodine, but the direct and reflex effects of the injection on the spinal cord may have had much to do with the result.