This section is from the book "Materia Medica: Pharmacology: Therapeutics Prescription Writing For Students and Practitioners", by Walter A. Bastedo. Also available from Amazon: Materia Medica: Pharmacology: Therapeutics: Prescription Writing for Students and Practitioners.
Iodine (iodum), 1/10 grain (0.006 gm.)-
Compound solution of iodine (Lugol's solution), an aqueous solution of 5 per cent, of iodine and 10 per cent. of potassium iodide.
Iodoform, Chi3, 4 grains (0.25 gm.).
Iodipin, sajodin, and iodival are iodized fats. Iodalbin and iodocasein are iodized albumins. According to Leathes (1911) iodipin can be absorbed and stored up as fat without giving up its iodine to the tissues. McLean found that iodine derivatives of fats and fatty acids are held in part by the lipoids of the cells. The iodized albumins are better borne by the stomach than the alkaline salts, but have no other differences in action. The dose of iodipin is 1 dram (4 c.c.) in emulsion, that of sajodin, iodival, and iodocasein is 10 grains (0.7 gm.).
The alkaline iodides are freely soluble in water and have a disagreeable bitter taste and a salt action. Locally they are irritant, so require proper dilution before their administration. They have always been considered valuable remedies, but their mode of action has been the subject of much surmise, It is generally understood that they promote the flow of saliva and respiratory mucus, that they increase the activity of the thyroid gland, and that they tend to lessen the viscosity of the blood. Mueller and Inada hold that the viscosity is lessened, but Determann says not. Adam thought that ordinary doses were too small to cause decreased viscosity, though large amounts would do so. Jorns and also Boveri find that small doses for long periods lessen the viscosity.
Absorption and excretion are rapid, iodine being recoverable from the saliva and urine a few minutes after their ingestion. Hanzlik (1912) found that with sodium iodide in 1 to 10 per cent, solution there was a rapid initial absorption of 50 to 75 per cent. of the total, and then a marked inhibition of absorption due to a local effect on the absorbing epithelium. He found also that the application to the mucous membrane of 0.2 to 1 per cent. sodium chloride prevented absorption of the iodide.
Unlike many salts, they do not remain in the body, but are excreted rapidly by the kidneys. Seventy-five per cent. of the dose appears in the urine inside of twenty-four hours. The remainder may remain in organic combination in the body. In fatty combination they are held by the lipoids of the cells for a longer time. The excretion is much retarded in chronic passive congestion of the kidneys and interstitial nephritis. Iodine is not found in the cerebrospinal fluid, even after very large doses by mouth.
Because of its excretion in the saliva, it may produce a very unpleasant metallic taste in the mouth, with coated tongue. To avoid this it is recommended to gargle with a solution of sodium bicarbonate during the iodide administration.
(See next article on Thyroid Gland.)
Marine and Lenhart (1909) found that iodine given in any form was taken up by the thyroids, whether these were normal, colloid, or hyperplastic; that the subjects with hyperplastic glands lost weight for one or two weeks, then rapidly gained; and that iodine hastened the tendency of all active hyperplasias to revert to colloid.
Many of the experiments have suggested that much of the benefit of iodides in a number of conditions may be due to increased thyroid activity.
In normal persons or laboratory animals iodides have no measurable effect upon the blood-pressure, but in those with high arterial tension they have a tendency to lower it. This effect is probably due both to the lessening of the viscosity of the blood and to the increase in thyroid activity. Their value in arteriosclerosis may possibly be due to improved blood-flow in the vasa vasorum, owing to diminished viscosity of the blood. From sodium iodide Macht found a stimulating effect on the heart and arteries, and from potassium iodide a depressing effect.
There is increased fluidity of mucus in the nose, throat, and bronchi. This is considered by Henderson and Taylor (1910) to be a reflex effect. In tuberculosis, iodides are believed to be harmful, because of their tendency to interfere with connective-tissue formation and to soften the caseous matter; for this promotes the spread of the disease. In cases with doubtful physical signs of tuberculosis it is a common custom to administer iodides to "bring out the rales." But the author's clinical experience coincides with that of others in finding this a dangerous practice, and the experiments of Sorel (1909) give additional proof that tuberculosis is a contraindication to iodide. Sorel infected guinea-pigs with the tubercle bacillus, then administered potassium iodide to a certain number of them. The iodide pigs died of tuberculosis some weeks earlier on the average than those which did not get the iodide. It has been reported also that weak doses of iodide in the tuberculous will give a reaction similar to that of fair doses of tuberculin, a reaction which may help to establish a diagnosis, but is not without danger. Iodide is said also to give such a reaction in lepers. A positive luetin reaction can be obtained in those taking iodide.
In asthma associated with chronic bronchitis and emphysema the action of iodides is probably an expectorant one.
Necrotic tissues in syphilis (gumma) and tuberculosis (caseous areas) take up more iodine than other tissues, and Jobling and Petersen find that both in the blood and the necrotic material iodine combines with and renders inert the antitrypsin which is the normal preventive of the resolution of necrotic tissue. As a result the caseous matter is subjected to attacks by the tryptic ferments and is digested and absorbed, the contained bacteria being set free. In the case of syphilis iodides are valuable because the gummata are absorbed and the contained bacteria are rendered accessible to germicidal agents such as mercury or salvarsan. In the case of tuberculosis of the lungs iodides are prone to be harmful, for as the cheesy matter is absorbed tubercle bacilli are set free and may spread the infection or be expectorated; furthermore, arteries in the caseous areas, having lost their support, may rupture and cause hemorrhage.