Vitamin K is a fat-soluble vitamin essential for the synthesis of several clotting factors (II, VII, IX, X) and proteins involved in bone metabolism (osteocalcin, matrix Gla protein). In the Indian context, it is critical for managing hemorrhagic disease of the newborn (HDN) and reversing the effects of vitamin K antagonists like warfarin. The 'NA' designation typically refers to the natural forms: K1 (phylloquinone) from plants and K2 (menaquinones) from bacterial synthesis and animal products, as opposed to synthetic K3 (menadione).
Adult: **Deficiency:** Oral: 5-25 mg daily. IM/SC: 2-10 mg, may repeat after 6-8 hrs if INR not corrected. **Warfarin Over-anticoagulation (INR > target):** INR 4.5-10 (no bleeding): Oral 1-2.5 mg. INR >10 (no bleeding): Oral 2.5-5 mg. Serious Bleeding/INR >20: IV 5-10 mg (slow infusion over 20-30 min) + Prothrombin Complex Concentrate (PCC) or Fresh Frozen Plasma (FFP).
Note: **Oral:** Administer with food containing fat to enhance absorption. **IM/SC:** Preferred for prophylaxis and non-urgent deficiency. Use deep intramuscular injection. In newborns, use the anterolateral thigh. **IV:** Reserve for emergencies. MUST be diluted and infused SLOWLY (e.g., 1 mg/min) to minimize risk of anaphylactoid reactions (flushing, dizziness, hypotension, dyspnea).
Vitamin K acts as an essential cofactor for the hepatic microsomal enzyme gamma-glutamyl carboxylase. This enzyme catalyzes the post-translational carboxylation of specific glutamic acid (Glu) residues to gamma-carboxyglutamic acid (Gla) residues on precursor proteins. This carboxylation is critical for the calcium-binding ability of these proteins, enabling their biological activity.
Pregnancy: Category C (US FDA). Vitamin K1 crosses the placenta poorly. Considered safe when used in recommended doses. Used to treat maternal vitamin K deficiency or warfarin over-anticoagulation. Prophylactic use in pregnant women on anticonvulsants (phenytoin, carbamazepine) may be considered.
Driving: No known effects. However, rapid IV infusion can cause dizziness; patients should be cautioned not to drive immediately after such administration.
| Warfarin / Acenocoumarol | Vitamin K is the specific antidote. It reverses the anticoagulant effect, leading to decreased INR. Concomitant use for deficiency can cause therapeutic failure of the anticoagulant. | Major |
| Broad-spectrum Antibiotics (e.g., Cephalosporins, Fluoroquinolones) | Can reduce gut bacterial synthesis of Vitamin K2, potentially increasing requirements and enhancing warfarin effect. | Moderate |
| Bile Acid Sequestrants (Cholestyramine, Colestipol) | Reduce absorption of fat-soluble vitamins including Vitamin K, potentially leading to deficiency. | Moderate |
| Orlistat | Reduces absorption of fat-soluble vitamins. Patients should take a multivitamin containing Vitamin K at least 2 hours before or after orlistat. | Moderate |
| High-dose Salicylates | May potentiate hypoprothrombinemia and increase bleeding risk. | Moderate |
Same composition (Vitamin K (NA)), different brands: