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.
Dr. Graves was one of the first to indicate the value of iodide of potassium in rheumatism, and it is now well established. I connect its efficient anti-rheumatic action mainly with an eliminant action through the kidneys, and to promote this, recommend it to be largely diluted and combined with bicarbonate of potash in acute cases. To prevent irritation of the stomach, the medicine may be given in an effervescent form. Sometimes, if the patient be feeble, and the urine abundant and of low specific gravity, the iodide may be combined with hydrochloric acid and quinine, as recommended by Dr. Southey. When effusion has occurred into the pericardium or the joints, tincture of iodine or iodides are certainly indicated. In muscular rheumatism they are useful, especially in those cases where the pains are made worse by warmth. This is one character of periosteal and syphilitic pain, and possibly some of the good results obtained from iodide of potassium in cases of chronic painful joints, sciatica, and lumbago, may be explained by its removing a latent specific or mercurial, or other metallic taint. In cases of chronic rheumatism, small doses of iodide, continued for a long time, often act exceedingly well; but some patients are very sensitive to its physiological action, and need special care to secure its toleration (v. pp. 68, 94).