phytomenadione
vitamin K· Brands: Konakion, AquaMEPHYTON, MephytonIMIVPO
Mechanism of action
Phytomenadione (vitamin K) is a cofactor for the gamma-carboxylation of glutamic acid residues on clotting factors II, VII, IX, X and proteins C and S. This post-translational modification is essential for the calcium-dependent interaction of these proteins with phospholipid membranes, enabling normal haemostasis.
Pharmacokinetics
Phytomenadione is well absorbed after oral administration when bile salts are present, but absorption is variable. Parenteral administration is used when rapid effect is needed or oral absorption is impaired. After IV administration, the onset of action on clotting factor synthesis occurs within hours, with maximal effect at 12 to 24 hours. It is metabolised in the liver and excreted in bile and urine. The plasma half-life is about 6 to 10 hours.
Indications & dosing
Vitamin K deficiency bleeding in adults
Administer by slow IV injection; monitor INR and repeat if necessary.
- adult · IV: 5–10 mg single dose · Administer by slow IV injection; monitor INR and repeat if necessary.
Warfarin reversal (major bleeding)
Give immediately with clotting factor replacement if available; repeat based on INR.
- adult · IV: 5–10 mg single dose · Give immediately with clotting factor replacement if available; repeat based on INR.
Warfarin reversal (elevated INR without bleeding)
Lower doses for INR 5-8, higher for INR >8; oral route can be used for non-urgent cases.
- adult · IV: 1–5 mg single dose · Lower doses for INR 5-8, higher for INR >8; oral route can be used for non-urgent cases.
Neonatal haemorrhagic disease prophylaxis
Administer within 1 hour of birth; repeat dose for preterm or breastfed infants according to local protocol.
- neonatal · IM: 1 mg single dose · Administer within 1 hour of birth; repeat dose for preterm or breastfed infants according to local protocol.
Neonatal haemorrhagic disease treatment
Slow IV injection; repeat if bleeding persists, check coagulation.
- neonatal · IV: 1–2 mg single dose · Slow IV injection; repeat if bleeding persists, check coagulation.
Contraindications & precautions
- Known hypersensitivity to phytomenadione or any excipient · Includes anaphylactic reactions to vitamin K.
- Severe hepatic impairment · Response may be inadequate as the liver cannot synthesise clotting factors.
- Intravenous administration should be given slowly and diluted; monitor for anaphylaxis, especially in patients with a history of allergy.
- In severe liver disease, monitor clotting parameters as response may be poor.
- For warfarin reversal, follow local protocol and monitor INR.
- In neonates, use caution with high doses due to risk of kernicterus.
Adverse effects
- Injection site pain
- Anaphylactic reactionserious
- Bronchospasmserious
- Hypotensionserious
- Hyperbilirubinemia in neonatesserious
- Haemolysis in neonatesserious
Renal & hepatic adjustment
- Hepatic impairment (severe): No dose adjustment; however, response may be reduced in severe hepatic impairment because hepatic synthesis of coagulation factors is impaired.
Monitoring, pregnancy & toxicity
- International Normalised Ratio (INR) or prothrombin time · Within 24-48 hours after administration, then as clinically indicated.
- Clinical signs of bleeding (melaena, petechiae, etc.) · Regularly during therapy.
- Haemoglobin (if bleeding occurs) · As clinically indicated.
- Pregnancy: Safe in pregnancy at therapeutic doses; used to manage anticoagulant-induced haemorrhage and to prevent neonatal haemorrhagic disease. No teratogenic effects reported.
- Toxicity: Rapid IV administration may cause hypotension, tachycardia, and anaphylactic shock. · Administer slowly (rate not exceeding 1 mg/min); stop infusion and treat anaphylaxis if it occurs.
Clinical notes
Used for the treatment of vitamin K deficiency, which can arise from malabsorption, liver disease, or antibiotic therapy, and for the management of bleeding or overdose related to warfarin or other oral anticoagulants. In life-threatening bleeding, fresh frozen plasma or prothrombin complex concentrate may be needed in addition to phytomenadione. For neonates, prophylactic vitamin K is given to prevent haemorrhagic disease of the newborn. Large doses can cause resistance to subsequent warfarin therapy, so use the lowest effective dose.
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BNF; local formulary