This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
External: - Solutions of iron salts are antiseptic. They have no action on the unbroken skin, but when applied locally to the abraded skin, sores, ulcers, and mucous membranes, the ferric salts are powerful astringents, because they coagulate albuminous fluids, both those discharged from the surface and also those in the tissue itself. There is no direct effect on the walls of the vessels, but the contraction of the coagulated albumin compresses them and diminishes their calibre. Partly for this reason, but still more because these iron salts quickly cause the coagulation of blood, and the clot thus formed plugs the bleeding vessels, they are the most perfect local haemostatics we possess, and will often arrest very severe haemorrhage. Ferric chloride, the nitrate, and sulphate are all very strongly astringent; but the scale preparations, reduced iron, the carbonate, iodide, phosphate and acetate are so very feebly astringent that they are never used as local applications; in fact, to most persons they are non-astringent. Ferric oxides have the property of converting oxygen into ozone, and are therefore disinfectant.
Mouth. - Preparations of iron have a styptic taste, the teeth and tongue may be blackened when they are taken, owing to the formation of ferrous sulphide, the sulphur being derived from the food and the tartar on the teeth; hence it is advisable to take iron preparations through a glass tube and immediately afterwards to brush the teeth. The free acid in the tincture of ferric chloride will destroy the enamel of the teeth, even if diluted with eight parts of water. The astringent preparations have, when locally applied, the same action on the mucous membrane of the mouth as on the raw skin.
Whatever form of iron is given by the mouth, it is converted in the stomach into ferric chloride, with probably a little ferrous chloride. Long experience has shown that ferric chloride is to the physician a most valuable preparation of iron; probably this is because it will not abstract hydrochloric acid from the gastric juice, as is the case with all other preparations of iron. It is often stated that an iron albuminate is formed in the stomach; this is incorrect, and when the iron albuminate is given by the mouth it will be converted into a chloride in the stomach. Although whatever form of iron is administered ferric chloride is formed in the stomach, the choice of the preparation is a matter of great importance, for if strongly acid salts are given, the acid set free after the formation of the chloride will act as a caustic, and damage the mucous membrane; even the preparations of the chloride may do this, for they always contain a considerable amount of free acid. These facts explain why iron preparations, especially the acid ones, so often cause headache, nausea, loss of appetite, and other symptoms of severe indigestion. We also learn why experience has taught that the sulphate, which is so often used, should be given in the form of a pill, for this, if specially coated, is not dissolved till the intestine is reached, and the acid is harmless in the alkaline solutions of that part of the alimentary canal. Further, we see why the preparations which are either not acid at all or only very slightly acid, such as reduced iron, dialyzed iron, not official, ferrous carbonate and the scale preparations, do not as a rule cause indigestion but it can also be said that they are generally not so efficient as the stronger preparations. However, this free acid may be neutralized by the addition of sodium bicarbonate, so that the tincture of ferric chloride will be acid only so far as the basic ferric chloride has an acid reaction; nor does this neutralization impair its therapeutic properties, for hydrochloric acid is added to it in the stomach. An effective preparation is now made, in which these disadvantages of the tincture of ferric chloride are removed, which is known as Weld's syrup of ferric chloride. Ferric chloride is very astringent, hence the astringent effect on the stomach of iron salts. The non-astringent preparations can only be astringent in proportion to the amount of ferric chloride formed from the gastric juice; but if large quantities of astringent preparations are given, the excess which is not decomposed by the gastric juice will add its astringency to that of the ferric chloride formed in the stomach.
On passing into the intestines, the contents of which are alkaline from sodium carbonate, ferric chloride becomes ferric oxide, which remains in solution owing to the presence of organic substances; ferrous chloride is converted into ferrous carbonate, which is also soluble. Lower down in the intestine, by the action of the sulphur compounds, the nascent hydrogen, and other readily oxidizable products of decomposition there present, these iron compounds are converted into ferrous sulphide and tannate (the tannic acid being derived from the vegetables in the food), and as such are eliminated with the faeces, which are turned black. Large amounts of the astringent preparations have a constipating effect; this may be owing to there being an excess of them, for the oxides and carbonates are non-astringent preparations.
Iron is certainly taken up from the alimentary canal, for the growing child gets from its food all the iron necessary for its increase in weight, but as the total amount of iron in the adult body is only about 38 grains 2.46 gm., it is probably absorbed very slowly in very minute amounts, and as iron in food exists as organic compounds, there is no doubt about the absorption of organic iron.
Whether, however, inorganic iron salts can be absorbed has been much discussed. The prevailing opinion, founded chiefly on histological evidence, now is that they can be taken up by the intestinal epithelium and passed into the leucocytes of the blood in minute particles. A little of this iron is deposited in the spleen, but more goes to the liver, where it is built up into complex bodies - one of which is called haematin - which are the precursors of haemoglobin; where in the body this is finally made is not known, but the red marrow utilizes it to make red blood-corpuscles.
The other opinion is that inorganic iron salts are not absorbed. The chief reason for this view is that the giving of such salts by the mouth does not lead to more iron in the urine; but we now know that this is because in such a case the excess of iron taken up is excreted into the intestine as an organic compound, and as it has been shown that under all circumstances the bile contains the merest traces of iron this excretion must take place by the intestinal mucous membrane.
It is often stated that the administration of iron causes, in healthy subjects, an increase in the number of red blood-corpuscles, but this is very doubtful. Probably in health it has little or no effect on the blood.
Iron salts injected into animals subcutaneously or directly into the veins cause gastro-intestinal irritation and paralysis from depression of the central nervous system. Part of the iron is stored up, but much is excreted by the gastro-intestinal mucous membrane.
In certain forms of anaemia (a condition in which the amount of haemoglobin and the number of corpuscles are diminished), especially chlorosis, the administration of iron rapidly improves the blood in both respects. It is therefore said to be haema-tinic; and as an improvement in the quality of the blood leads to an improvement in the functions of all the organs of the body, iron is also called a tonic. Tonics are drugs which indirectly improve the action of the several organs of the body; usually they act by improving the quality of blood or by aiding digestion, and thus rendering the digestion and absorption of the food more easy (see p. 115). If, as already stated, inorganic iron is directly taken up by the intestinal epithelium and passed to the leucocytes, the benefit in anaemia is easy to understand. But we have seen that some believe that inorganic iron is not absorbed, and if this be so, it is at first sight difficult to understand how it can benefit anaemia. As the organic iron in food must be absorbed we may conclude that it is in some way or other protected from decomposition in the alimentary canal, if we believe that the inorganic compounds which would result if they were decomposed are incapable of absorption. Bunge's hypothesis is, that in some forms of anaemia, especially chlorosis, organic salts of iron taken in the food are in some way split up in the intestines so as to be incapable of absorption. In those anaemic conditions which can be benefited by iron the administration of the inorganic salts prevents the decomposition of the organic salts in the food by fixing the decomposing agents, which, according to Bunge, are chiefly alkaline sulphides and forming iron sulphide. This, he says, is supported by the fact that to cure chlorosis rapidly, enormous doses of iron are often found to be necessary; for example, a patient will take 6 gr. .40gm. of reduced iron three times a day, or 18 gr. 1.20 gm. a day. Now, the whole amount of iron in the blood of an ordinary healthy woman is about 38 gr. 2.46 gm., for there is only one atom of iron in a molecule of haemoglobin, which contains considerably over 2000 atoms. Supposing she had lost half her haemoglobin, if the iron given were simply absorbed, one day's treatment would speedily restore her health, but it is well known that weeks are often required. But if this view were correct we should expect that bismuth, manganese, or arsenic, by fixing the decomposing agents, would cure chlorosis as efficiently as iron. It has been stated that they will, but Stockman has published results that point in a contrary direction, and he has shown that iron sulphide will cure chlorosis, although on Bunge's hypothesis, it should not; for it will not fix the decomposing agents if they are alkaline sulphides. Further, many think that it is not necessary to give large doses of iron to cure chlorosis. Iron injected subcutaneously cures chlorosis, but this does not point in one direction more than another, for it may be excreted into the intestine, and there fix the alkaline sulphides. On the whole, the evidence seems against Bunge's view.
As iron in anaemic subjects increases the amount of haemoglobin, more oxygen is carried to the tissues, and thus the whole body shares in the benefit of a course of iron, which has also been thought to have a direct effect on the kidneys as a mild diuretic, and a direct effect in promoting the menstrual flow. These actions are, however, slight, and may be due to the general improvement in health. Iron salts have been given to produce abortion, but without any result. Remote astringent effects have been attributed to them, but there is no satisfactory proof that they have any; and, indeed, when we remember that very little if any iron is absorbed in an astringent form, and it cannot exist in the blood in such a form, we should hardly expect that iron salts could be remotely haemostatic or astringent. Iron is chiefly stored in the spleen, lymphatic glands, liver and marrow; possibly it is by stimulating the activity of this that iron cures chlorosis.
One milligramme 1/64 gr. of iron is eliminated daily in the urine, and this remains constant under all circumstances. Any excess of elimination following subcutaneous injection, or excessive absorption from the intestine, takes place through the intestinal mucous membrane.