Preparation

Iodide of iron is prepared by simply mixing the two ingredients together, with the presence of water, which dissolves the resulting compound, and, after filtration, yields it by evaporation. The iron is employed in the state of filings, or of wire; but the latter is preferable, as it is in general purer. The preparation consists of one equivalent of iron, one of iodine, and five of water; but, if considerable heat is employed in drying it, the proportion of water is smaller. It should be kept in a well-stopped bottle.

Properties

When the solution of iodide of iron is very carefully evaporated, with the exclusion of atmospheric air, the salt is obtained in the form of green, transparent, tabular crystals; but, as ordinarily prepared, it is a greenish-black substance, of an astringent chalybeate taste, very deliquescent, and very soluble in water and alcohol. At a moderate heat it melts, and on cooling solidifies into a dark-gray, crystalline mass, of a metallic lustre. At a higher heat, with exposure to the air, it is decomposed; the iodine escaping, and the iron absorbing oxygen, and remaining behind as the sesquioxide. Upon the slightest exposure to the air, even at ordinary temperatures, the iron attracts oxygen and passes into the state of sesquioxide, while the iodine becomes free. Analogy would lead to the supposition that, as in the case of the protochloride of iron, the metal would be divided between the oxygen absorbed, and the principle previously combined with it, forming the sesqui-iodide and sesquioxide; but that iodine is liberated is shown by the fact, that the altered substance colours starch blue. This change has almost always happened, in some degree, with the iodide of iron of the shops, which, on that account, is seldom entirely soluble in water.

A solution of the iodide undergoes this change much more rapidly than the solid salt, quickly depositing the sesquioxide, and thus becoming weakened as a chalybeate. There are, however, two means of protecting the solution against this change; one by introducing into the bottle containing it some iron filings, or a coil of iron wire, the other by incorporating it with a considerable proportion of sugar. A solution protected in the latter method is officinal, and will be described. In the former method, the free iron immediately takes all the oxygen which that of the iodide absorbs from the air; and the protiodide, therefore, remains unchanged in the solution.

Incompatibles. Precipitates are produced in the solution of iodide of iron by the alkalies and their carbonates, lime-water, magnesia, soaps, hydrosulphuric acid and the soluble sulphurets, ferrocyanide of potassium, the soluble salts of lead, copper, silver, and mercury, but not those of zinc, by the soluble phosphates, all the astringent vegetable infusions, and many other organic substances.

Effects on the System

Iodide of iron has both the topical and constitutional effects of the other soluble salts of the metal, increasing the appetite, improving digestion, enriching the blood, and operating generally as a tonic; but it is less astringent than the sulphate, and probably less so than the nitrate or chloride; and, moreover, possesses peculiar properties quite distinct from its powers as a chalybeate, and attributable to the iodine it contains. These are evinced in its alterative. diuretic-, and laxative effects. Dr. A. T. Thompson states that, shortly after its administration in large doses, both iron and iodine may be found in the urine; but it is not mainly in the form of iodide of iron that it is thus thrown off. The experiments of Quevenne show that but a small portion of the metal passes by the kidneys, while the iodine passes abundantly; proving that the two constituents are separated in the system, and most of the iron retained. (Arch. de Physiol. de Bouchardat, Oct. 1854, p. 104.) We can thus explain the two classes of effects produced, one belonging to the chalybeate ingredient, the other to the iodine. In over-doses, iodide of iron proves irritant to the stomach and bowels, causing epigastric uneasiness, nausea, vomiting, purging, and griping pains. Very largely taken, it would probably induce serious gastro-intestinal inflammation; though I have seen no account of positively poisonous effects.

Therapeutic Application

This medicine was first employed by Dr. Pierquin so early as in the year 1824. It is now among the most popular of the chalybeates, though employed chiefly in a special class of cases. It may be used as a gastric tonic in dyspepsia, or with a view to the general effects of iron on the system, as in simple chlorosis, or in the anemic condition attended with amenorrhoea, leucorrhoea, etc.; but its best effects are displayed in cases of scrofulous disease, and other forms of local tumefaction or induration, in which there is at the same time an indication for the improvement of the blood. It is only in the absence of all febrile excitement and gastric inflammation, that it should be resorted to in such cases; but, when properly accommodated to the state of the system, it is an excellent remedy. In swellings of the lymphatic glands external or internal, diseases of the bones, ligaments, and joints, and ulcerative and eruptive affections of the skin, when these can be traced to a scrofulous taint; in chronic enlargement of the thyroid gland, mamma, testicle, ovary, liver, and spleen; in various subacute or chronic swellings and indurations without special seat, or known peculiarity of character; in all these affections, it may be considered as indicated when they exist conjointly with an anemic state of the blood, and a general deficiency of vital force. Without this associated condition, and in all cases in which the excitant properties of the chalybeate on the system may be contraindicated, some other preparation of iodine, especially iodide of potassium, should be preferred. Iodide of iron has also been used with advantage in secondary syphilitic affections, in like manner connected with anemic debility. It is said, moreover, to have been successfully employed in diabetes. A solution of it containing from one to two drachms in a pint of water, has been employed locally as an injection in gonorrhoea and leucorrhoea, and as a lotion in ulcers.

Administration

The dose of iodide of iron is two or three grains three times a day, which may be increased to ten grains, if not found to disturb the stomach. The administration of it, in the pilular form, is attended with some difficulty, in consequence of its deliquescent property, and extreme proneness to chemical change. Various modes of obviating these objections have been proposed Perhaps the best method would be to evaporate to a pilular consistence the officinal solution of the iodide, which is protected from change by sugar; or the preparation might be directly incorporated with sugar when made into pills; or, as suggested by Prof. Procter, a little reduced iron might be added to the mass with the same view. But, even though protected against oxidation, the pills would still be liable to deliquescence. To obviate both disadvantages, they might be covered with a coating of impervious matter, by dipping them into a chloroformic solution of caoutchouc and drying them. It will be noticed, in the following paragraph, that these suggestions have been carried into effect in the recent revision of the U. S. Pharmacopoeia, even to the impervious coating, though the material for coating the pills is not the one here proposed, and is probably preferable to it.

Pills of Iodide of Iron (Pilulae Ferri Iodidi, U. S.) are ordered by our officinal code to be made by first forming the iodide in strong solution by a direct combination of the two ingredients, then incorporating the solution with a little reduced iron, sugar, and marshmallow in powder, and finally evaporating to a pilular consistence, and dividing into pills. These are directed to be coated with balsam of Tolu, which to a considerable extent preserves them from the injurious influence of the air, while the reduced iron and sugar still further protect them from the oxidation of the iron. Each pill contains about a grain of the iodide of iron and one-fifth of a grain of reduced iron. Two or three of them may be taken two or three times a day.

Syrup of Iodide of Iron (Syrupus Ferri Iodidi, U. S., Br.). - Solution of Iodide of Iron (Liquor Ferri Iodidi, U. S. 1850). This is directed by the U. S. Pharmacopoeia to be prepared by dissolving iodine and iron filings together in water, filtering the solution into a certain proportion of syrup, in a bottle, previously heated to 212°, and then adding sufficient syrup to produce the requisite measure. This preparation differs from the solution of iodide of iron of the U. S. Pharmacopoeia in having a larger proportion of sugar, which was needed for its preservation, and which is now sufficient to authorize the preparation to be placed among the syrups. It is on the whole the most convenient form for the administration of iodide of iron.

The syrup is transparent, and of a pale-green, or yellowish-green colour, and without sediment. By exposure to light, in a closely stopped bottle, it becomes nearly colourless. It is the common form for the administration of iodide of iron, and is greatly preferable to the pill. When it is swallowed, care should be taken to wash out the mouth well, in order to avoid possible injury to the teeth. The dose of the U. S. preparation is from twenty to forty minims, which should be diluted with water, but only at the moment of exhibition.