Pharmacokinetics and Iron Metabolism
Once in the body, iron binds to transferrin, a $\beta$-globulin produced in the liver. This protein transports the micronutrient to the tissues. The major portion is directed to the bone marrow for hemoglobin biosynthesis, while the remainder is utilized by enzyme systems and for myoglobin production.
Excess iron is stored in the organs of the reticuloendothelial system (bone marrow, liver, spleen). Iron is excreted primarily via bile and shedding gastrointestinal epithelium, and to a lesser extent through the kidneys and sweat glands. Women have a higher physiological requirement for this micronutrient due to regular losses from menstruation and lactation.
Oral Preparations and Combinations
The base substance is ferrous sulfate, which contains the divalent ionized element ($Fe^{2+}$). It is rarely used as monotherapy. To improve bioavailability in iron-deficiency hypochromic anemia, combination products with adjuvants are used:
- With ascorbic acid (Ferroplex): vitamin C reduces trivalent iron ($Fe^{3+}$) to divalent iron ($Fe^{2+}$) and increases gastric juice acidity, enhancing ionization.
- With surfactants (Conferon): sodium docusate reduces surface tension, facilitating absorption.
- With mucoprotease (TardYferon): the enzyme additionally stimulates ion assimilation.
Prolonged-release forms exist where the active substance is enclosed in a polymer matrix for gradual release (Ferro-Gradumet), as well as preparations based on other salts such as fumarate (Heferol, Ferretab) and lactate (Hemostimulin).
Administration Guidelines and Drug Interactions
Iron therapy requires strict adherence to the dosing regimen. Medications are prescribed in solid forms (capsules, dragees, tablets) to avoid direct contact with the teeth.
Preparations should 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, phytate, and phosphoric acid.
Treatment is always prolonged. It should not be discontinued merely upon the normalization of hemoglobin levels, but only after complete replenishment of tissue stores, which must be confirmed by mandatory monitoring of serum iron.
Side Effects and Contraindications
Enteral administration is often accompanied by adverse gastrointestinal reactions: anorexia, nausea, vomiting, metallic taste, and abdominal pain. A characteristic side effect is constipation. This occurs because iron ions bind intestinal hydrogen sulfide ($H_2S$), which normally acts as a natural stimulant of peristalsis.
Prescribing these agents is contraindicated in:
- Hemolytic anemia (since the underlying issue is not an iron deficiency).
- Chronic kidney and liver pathologies.
- Inflammatory and ulcerative gastrointestinal lesions (ulcerative colitis, peptic ulcer disease) due to the severe irritant effect on the mucosa.
Parenteral Administration
If oral administration is impossible due to poor tolerance, malabsorption, or the need for rapid deficiency correction, injections are used. For example, Ferrum Lek is available in two forms:
- Intramuscular (iron(III)-hydroxide polymaltose complex) — administered every other day.
- Intravenous (iron sucrose complex) — administered slowly.
Parenteral administration carries specific risks. Locally, phlebitis, venous spasm, and post-injection abscesses may develop. Systemic reactions include hypotension, fever, chest pain, and muscle and joint pain (arthralgia).