This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Melsens found that every mercurial compound was soluble in an alkaline or neutral solution of iodide of potassium, and that corrosive sublimate, for instance, if fixed in a muscle, tendon, etc., could be dissolved out of the organic tissue by soaking it in such iodide solution. Also, that even metallic lead was, to some extent, soluble in the same medium, with formation of a double iodide of lead and potassium (Medico - Chirurgical Review, i., 1853). Hence, he argued that in cases of mercurial or lead-poisoning, with salivation, tremor, colic, palsy, etc., iodides introduced into the blood could form soluble compounds with metal deposited in the tissues, and enable this to be taken up by the absorbents and passed out by the kidneys and other channels of excretion. Support has been given to this argument by the fact that an insoluble salt of mercury or lead may be given to animals without evident effect until after the administration of an iodide, when the recognized symptoms of poisoning appear. Further, we know, clinically, that sometimes in metallic cachexia, when active symptoms are no longer present, and the poisons are not detectable in the secretions, if an iodide be given, acute mercurial or lead-action may be developed, and the foreign substances may be found in the urine, etc.
Only chronic conditions of illness, such as palsy or cachexia, may be present when the iodide is commenced, but in the course of a few days acute symptoms, such as colic or salivation, may be reproduced until elimination is complete. But however the theory on the subject may stand, there can be no doubt that iodides often act well in plumbism, and, although I have not always succeeded with them, I have had some good results. The case of M. Faure, recorded by himself, is a good illustration of their value: engaged in white-lead manufacture, he suffered severely from the ordinary symptoms of plumbism, and cured himself with iodide of potassium. He remarks that he could tolerate the drug better when he took it before, than with food, which he attributed to the "fasting stomach being coated with mucus" (Medical Record, 1876).
Dr. H. Thompson has given the details of a case of plumbism, in which iodide of potassium, on three or four occasions, led to relapse of colic at the same time that iodism was developed, and these attacks were always followed by improvement in the paralyzed extensor muscles, as if some of the metallic poison had been eliminated, though there is not a record of its detection in the secretions (British Medical Journal, i., 1871). Jacobs thinks the best results are obtained with the iodide in conjunction with emetic and purgative treatment (Medical Record, 1877).