Pharmacokinetics and Iron Metabolism
Once in the body, iron binds to transferrin, a $\beta$-globulin produced in the liver. This protein transports the trace element to the tissues. Most of it is directed to the bone marrow for hemoglobin biosynthesis, while the remainder is expended on the needs of enzyme systems and myoglobin production.
Excess substance is stored in the organs of the reticuloendothelial system (bone marrow, liver, spleen). Iron is excreted primarily via bile and exfoliating gastrointestinal epithelium, and to a lesser extent through the kidneys and sweat glands. In women, the physiological requirement for the trace element is higher due to regular losses during menstruation and lactation.
Oral preparations and their combinations
The base substance is ferrous sulfate, containing the divalent ionized element ($Fe^{2+}$). It is rarely used as monotherapy. To improve bioavailability in iron-deficiency hypochromic anemia, combination agents with adjuvants are used:
- With ascorbic acid (Ferroplex): vitamin C converts trivalent iron ($Fe^{3+}$) into divalent iron ($Fe^{2+}$) and increases gastric juice acidity, improving ionization.
- With surfactants (Conferon): sodium docusate reduces surface tension, facilitating absorption.
- With mucoprotease (Tardyferon): the enzyme additionally stimulates the assimilation of ions.
There are prolonged-release forms where the active substance is enclosed in a polymer sponge for gradual release (Ferro-Gradumet), as well as preparations based on other salts such as fumarate (Heferol, Ferretab) and lactate (Hemostimulin).
Administration rules and interactions
Iron therapy requires strict adherence to the regimen. Medications are prescribed in solid forms (capsules, dragees, tablets) to avoid direct contact with the teeth.
Preparations must be taken on an empty stomach (one hour before or two hours after a meal). Food can block absorption by forming insoluble complexes. The main antagonists are tannin in tea, calcium salts, phytin, and phosphoric acid.
Treatment is always prolonged. It is discontinued not upon simple normalization of hemoglobin levels, but only after complete replenishment of tissue stores, which is confirmed by mandatory monitoring of serum iron.
Side effects and contraindications
Enteral administration is often accompanied by adverse reactions from the digestive tract: anorexia, nausea, vomiting, metallic taste, and abdominal pain. A characteristic side effect is constipation. They occur because iron ions bind intestinal hydrogen sulfide ($H_2S$), which normally acts as a natural stimulator of peristalsis.
Prescribing these agents is contraindicated in:
- Hemolytic anemia (since the problem does not lie in iron deficiency).
- Chronic kidney and liver pathologies.
- Inflammatory and ulcerative lesions of the gastrointestinal tract (ulcerative colitis, peptic ulcer disease) due to the strong irritating effect on the mucous membrane.
Parenteral administration
If oral administration is impossible due to poor tolerance, malabsorption, or the need to urgently replenish the deficiency, injections are used. For example, the preparation Ferrum Lek is available in two forms:
- Intramuscular (iron polymaltose complex) — administered every other day.
- Intravenous (iron sucrose complex) — administered slowly.
Parenteral administration is associated with specific risks. Locally, phlebitis, venous spasm, and post-injection abscesses may develop. Systemic reactions include arterial hypotension, fever, chest pain, as well as muscle and joint pain (arthralgia).
Briefly: answers to topical questions
What are the contraindications for prescribing iron preparations?
Contraindications for prescribing enteral iron preparations include hematological, chronic, and inflammatory diseases.
- Hematological pathologies — hemolytic anemia, since the problem is not associated with iron deficiency.
- Chronic organ pathologies — liver and kidney diseases.
- Inflammatory and ulcerative lesions of the GI tract — peptic ulcer disease, ulcerative colitis, and chronic inflammation due to the risk of an irritating effect on the mucous membrane.
What systemic side effects may develop with parenteral administration of iron preparations?
Systemic reactions, allergies, and specific complications may develop with parenteral administration of iron preparations.
- Cardiovascular and general reactions — arterial hypotension, chest pain, fever, muscle and joint pain (arthralgia).
- Gastrointestinal disorders — dyspepsia.
- Immediate-type allergic reactions — up to the risk of developing anaphylactic shock.
- Hemosiderosis — pathological deposition of hemosiderin in tissues due to iron overload bypassing physiological absorption barriers.
What are the strict indications for parenteral administration of iron preparations?
Strict indications for parenteral administration of iron preparations are situations where enteral administration is impossible or ineffective.
- Refractoriness — absence of clinical and laboratory response to oral administration.
- Impaired absorption — malabsorption syndrome against the background of small intestine pathology.
- GI pathologies — exacerbation of peptic ulcer disease.
- Intolerance — individual intolerance to oral forms.
- Severe conditions — severe posthemorrhagic anemia.
- Urgent conditions — the need for forced restoration of hemoglobin levels, for example, in preparation for elective surgery.
Which iron salts, in addition to sulfate, are used as part of oral antianemic agents?
As part of oral antianemic agents, in addition to sulfates, other ferrous salts are used.
- Iron fumarate — part of the preparations Heferol, Ferretab, Fferronal.
- Iron gluconate — used in preparations Tot'Hem, Ferronal.
- Iron chloride — used in the preparation Hemofer prolongatum.
- Iron lactate — contained in the preparation Hemostimulin.
- Iron carbonate — also belongs to the applied iron salts.
What local complications are characteristic of intramuscular and intravenous administration of iron preparations?
The following local reactions are characteristic of parenteral administration of iron preparations:
- venous spasm;
- phlebitis;
- post-injection abscesses.
To remember the mechanism of constipation caused by iron preparations, imagine a chemical reaction: iron "steals" hydrogen sulfide ($H_2S$) in the intestine. No gas — no stimulation of peristalsis — a blockage occurs.
Class and exam questions
Why is it better to wash down iron preparations with water rather than tea?
Tea contains tannin, which is a potent absorption antagonist. It forms poorly soluble complexes with iron ions, blocking their absorption in the gastrointestinal tract.
When can iron therapy be discontinued?
Therapy is discontinued only after complete replenishment of iron stores in the body. The target should not be the normalization of hemoglobin, but rather serum iron levels.
Why is ascorbic acid added to iron preparations?
It reduces ferric iron to ferrous iron, which is absorbed significantly better, and also increases the acidity of the medium for better ionization.
Can iron preparations be prescribed for hemolytic anemia?
No, this is strictly contraindicated. In hemolytic anemia, red blood cells are destroyed, but there is no true iron deficiency in the body.
What else to study on this topic
- Mechanism of iron binding and transport by transferrin
- The role of the reticuloendothelial system in the storage of trace elements
- Comparative pharmacokinetics of iron sulfate, fumarate, and lactate
- Pathogenesis of systemic reactions during intravenous iron administration
- Interaction of iron preparations with food components at the biochemical level
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