Vitamin K1 acts as a cofactor for γ-glutamyl carboxylase, an enzyme that activates clotting factors II (prothrombin), VII, IX, and X by carboxylating glutamate residues. This post-translational modification enables these factors to bind calcium and participate in the coagulation cascade. Vitamin K1 also activates anticoagulant proteins C and S, maintaining hemostatic balance (Lippincott Textbook of Pharmacology).

1. Reversal of Warfarin Anticoagulation:
   • Manages bleeding or over-anticoagulation (e.g., INR >4.5) in patients on warfarin.
2. Vitamin K Deficiency:
   • Treats bleeding due to malnutrition, malabsorption, or prolonged antibiotic use.
3. Newborn Prophylaxis:
   • Prevents hemorrhagic disease of the newborn (1 mg intramuscular [IM] dose at birth).
4. Liver Disease:
   • Addresses clotting factor deficiency in cholestasis or cirrhosis (BNF).

Dosing varies by indication and route:

1. Warfarin Reversal:
   • INR 4.5–10 (No Bleeding): 1–2 mg orally; repeat if INR remains high after 24 hours.
   • Major Bleeding or INR >10: 5 mg IV (slow infusion over 10–30 minutes) + prothrombin complex concentrate (PCC).
2. Vitamin K Deficiency:
   • Adults: 10 mg IV/IM/orally; repeat as needed.
   • Children: 0.5–1 mg IV/IM.
3. Newborns:
   • Prophylaxis: 1 mg IM at birth (Lange Basic & Clinical Pharmacology).

Routes:

• IV: For emergencies (risk of anaphylactoid reactions; infuse slowly).
• Oral/IM: For non-urgent correction.

• Common:
  • Flushing, dizziness, or altered taste (IV route).
  • Pain at injection site (IM).
• Serious:
  • Anaphylaxis: Rare, associated with rapid IV administration.
  • Hyperbilirubinemia: Not linked to K1 (unlike synthetic K3).

• Contraindications: Hypersensitivity to Vitamin K1.
• Warnings:
  • IV Administration: Risk of anaphylactoid reactions; administer slowly (1 mg/min).
  • Newborns: IM route preferred for prophylaxis; oral regimens may require multiple doses.
  • Liver Disease: Impaired clotting factor synthesis may limit efficacy.
• Pregnancy/Lactation: Safe; crosses placenta and enters breast milk (BNF).

• Warfarin: Antagonizes anticoagulant effect.
• Broad-Spectrum Antibiotics (e.g., cephalosporins): Reduce gut flora-derived Vitamin K2, increasing K1 requirements.
• Bile Acid Sequestrants (e.g., cholestyramine): Impair absorption of oral Vitamin K1.
• Orlistat: Reduces fat-soluble vitamin absorption.

• Generic Name: Phytomenadione.
• Brand Names: Konakion (UK), Aqua-Mephyton (US), Kanokion (EU).