Mechanism of Action and Vitamin K Preparations
Vitamin K plays a pivotal role in the hemostatic system. It acts as a cofactor (in its hydroquinone form) in the γ-carboxylation of glutamic acid residues. This process is essential for the hepatic synthesis of functional procoagulants (factors II, VII, IX, X), natural anticoagulants (proteins C and S), and the bone matrix protein osteocalcin.
These reactions yield γ-carboxyglutamic acid residues capable of binding calcium ions. Without calcium, factors cannot anchor to platelet and endothelial membrane phospholipids, halting the activation cascade and causing hemorrhage. Hypovitaminosis leads to the synthesis of acarboxy-proteins—inactive factor precursors.
There are several forms of vitamin K:
- Natural (fat-soluble): vitamin K1 (phylloquinone of plant origin) and K2 (menaquinones synthesized by intestinal microflora).
- Synthetic: phytomenadione (an analogue of K1) and menadione (vitamin K3). The latter is a water-soluble provitamin, clinically used as vicasol (menadione sodium bisulfite).
These medications are indicated for hemorrhagic disease of the newborn, vitamin K antagonist overdose, and malabsorption syndromes. Administration requires caution: allergic reactions can occur, intravenous administration carries a high risk of anaphylactoid reactions, and in neonates, vicasol may provoke hemolytic anemia and hyperbilirubinemia.
Clotting Factor Concentrates
These agents form the basis of replacement therapy for inherited or acquired deficiencies. Because endogenous factors have a short half-life, patients require regular infusions.
- Factor VIII (haemofil M, immunate). Derived from plasma with double viral inactivation. Used for hemophilia A and von Willebrand disease. An alternative is cryoprecipitate—a plasma protein concentrate containing factor VIII, von Willebrand factor, and fibrinogen.
- Factor IX (aghemfil B, octanine, immunine). Purified plasma fractions for the treatment of hemophilia B and the reversal of vitamin K antagonist overdose.
- Factor VII (eptacog alfa activated / novoseven). A recombinant preparation effective in factor VII, V, II, IX, and X deficiencies.
The primary challenge with donor plasma-derived products is the risk of transmitting transfusion-transmitted infections (HIV, hepatitis). To mitigate this, modern practice increasingly shifts toward recombinant products.
For mild coagulopathies (e.g., mild hemophilia A), desmopressin serves as an alternative. This synthetic arginine vasopressin analogue stimulates the release of von Willebrand factor from the endothelium, which secondarily increases factor VIII activity.
Local and Herbal Hemostatics
Topical agents are used to stop capillary and parenchymal organ bleeding. Thrombin (isolated from donor plasma) and hemostatic sponges (based on collagen or gelatin) form a reliable mechanical matrix that rapidly facilitates clot formation.
Herbal hemostatics are widely used to manage uterine, pulmonary, renal, and intestinal bleeding. Pharmacological activity is provided by extracts, infusions, and tinctures of stinging nettle leaves, yarrow herb, water pepper (Persicaria hydropiper), smartweed, arnica flowers, and Lagochilus inebrians. These agents are administered both orally and topically.