Mechanism of Action and Metabolism
Unlike bacteria, which synthesize folic acid de novo from para-aminobenzoic acid (PABA), the human body cannot synthesize folic acid. Humans obtain it through diet (from plant and animal sources) or via synthesis by the intestinal microflora.
Vitamin B9 itself is inactive. In the liver, it undergoes bioactivation, converting into tetrahydrofolate (THF). This process is a cyclic pathway:
- Dihydrofolate is reduced to THF.
- The reaction is catalyzed by the enzyme dihydrofolate reductase (DHFR).
- THF acts as a coenzyme — a donor of one-carbon units (methyl and formyl groups).
- After donating the carbon unit, THF is oxidized back to dihydrofolate, and the cycle repeats.
Calcium folinate (Calcium folinate) is essentially a pre-formed active form (a derivative of THF). It immediately enters biochemical pathways, ensuring the synthesis of DNA and RNA precursors (purine nucleotides, thymidylate) and participating in amino acid metabolism (methionine, serine, glycine).
Pharmacological Effects
The primary pharmacological effect of the drug is anti-anemic.
By supplying cells with building blocks for nucleic acids, the drug:
- Supports normal proliferation (division) of rapidly renewing cells.
- Stimulates erythropoiesis by regulating the proper maturation of megaloblasts and their transition into normoblasts.
- Improves iron absorption in the gastrointestinal tract.
Indications for Use
The drug is prescribed for conditions associated with folate deficiency or disrupted folate metabolism:
- Antidote therapy: Reversing the toxic effects of folic acid antagonists (methotrexate, trimethoprim, triamterene, pyrimethamine). These drugs inhibit DHFR, and calcium folinate bypasses this enzymatic block.
- Hematology: Macrocytic hyperchromic anemia, leukopenia, and other types of anemias.
- Combination therapy: Oncological, neurological, and gastroenterological disorders (including malabsorption syndrome).
- Phthisiology: Reducing toxicity during tuberculosis treatment.
- Prophylaxis: Congenital and acquired hyperhomocysteinemia, as well as states with increased folate demand (pregnancy).
Adverse Effects and Strict Contraindications
Allergic reactions may occur during administration.
Critical Rule: When treating pernicious ($B_{12}$-deficient) anemia, folate preparations must always be prescribed in combination with cyanocobalamin (vitamin $B_{12}$).
Isolated monotherapy with folates in pernicious anemia is strictly contraindicated. The drug rapidly normalizes hematological parameters (blood counts) but completely fails to resolve neurological symptoms. Furthermore, this "false improvement" can allow neurological disorders to progress silently beneath the surface.
Administration Guidelines
According to reference data, Calcium folinate is available in ampoules as a 0.25% solution in 1 ml and 10 ml. The standard daily dose is 0.005 g (5 mg), administered intramuscularly or intravenously.
Calculation: A 0.25% solution contains 0.25 g of the substance in 100 ml, which equals 2.5 mg in 1 ml. To administer 0.005 g (5 mg), 2 ml of this solution is required.
Prescription Example (intramuscular, 1 ml ampoules): ```latin Rp.: Sol. Calcii folinatis 0.25% - 1 ml D.t.d. N. 10 in ampull. S. Intramuscularly, 2 ml (0.005 g) once daily. ```