Za Pharmacy
Drugs, Supplies and Delivery
Vitamin K1 (Phytomenadione)
Vitamin K1 (phytomenadione) is a fat-soluble vitamin essential for blood clotting and bone metabolism. This article details its mechanism of action, uses, dosage, side effects, precautions, drug interactions, and generic names, referencing the British National Formulary (BNF), Lippincott Textbook of Pharmacology, and Lange Basic & Clinical Pharmacology.
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).
- Reversal of Warfarin Anticoagulation:
- Manages bleeding or over-anticoagulation (e.g., INR >4.5) in patients on warfarin.
- Vitamin K Deficiency:
- Treats bleeding due to malnutrition, malabsorption, or prolonged antibiotic use.
- Newborn Prophylaxis:
- Prevents hemorrhagic disease of the newborn (1 mg intramuscular [IM] dose at birth).
- Liver Disease:
- Addresses clotting factor deficiency in cholestasis or cirrhosis (BNF).
Dosing varies by indication and route:
- 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).
- Vitamin K Deficiency:
- Adults: 10 mg IV/IM/orally; repeat as needed.
- Children: 0.5–1 mg IV/IM.
- 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).
