Antihaemorrhagic (vitamin K)
Phytonadione (vitamin K1) is the vitamin used to treat and prevent bleeding caused by vitamin K deficiency, including bleeding associated with anticoagulants (warfarin, acenocoumarol). It is given by injection (intramuscular, subcutaneous or slow intravenous) and its effect takes a few hours.
Also known as: vitamina K1, vitamin K1, Konakion, phytonadione, phytomenadione
Phytomenadione (vitamin K1) antagonises the anticoagulant effect of warfarin, lowering the INR.
Phytomenadione (vitamin K1) is the antidote to warfarin: it replenishes the cofactor needed to carboxylate factors II, VII, IX and X and reverses the anticoagulant effect, lowering the INR within hours. This interaction is intentional in the reversal of supratherapeutic INR or bleeding, but accidental (e.g. multivitamin supplements, vitamin-K-rich diet) causes INR instability and thrombosis risk. After vitamin K administration, warfarin may take days to weeks to return to therapeutic effect, and the dose must be re-adjusted with INR monitoring. In anticoagulated patients, advise consistency in vitamin K intake and review supplements.
Vitamin K (phytomenadione) directly antagonises warfarin and lowers the INR — it is the antidote used for reversal. Administer only with an indication (supratherapeutic INR or bleeding) and monitor re-anticoagulation.
Vitamin K replenishes the substrate for factors II, VII, IX and X, reversing warfarin's block.
Monitor INR and signs of thrombosis after reversal.
Subtherapeutic INR or thrombotic events after excessive reversal.
Use vitamin K1 as indicated (reversal, correction of supratherapeutic INR); reassess INR 24 h after.
DailyMed (FDA) — approved Phytomenadione label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c7ef968-2c76-4220-a9ec-3179d243c422 ; approved Warfarin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=541c9a70-adaf-4ef3-94ba-ad4e70dfa057 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Phytonadione (vitamin K1) can be administered with or without food; oral absorption improves when taken after a meal.
May be taken with or without food, consistently.
DailyMed/FDA (NIH/NLM) — approved Phytonadione label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c7ef968-2c76-4220-a9ec-3179d243c422
In patients anticoagulated with warfarin, variable intake of vitamin K-rich foods (green leafy vegetables) alters the INR; phytonadione supplementation is used as an antidote.
Keep vitamin K intake consistent; monitor the INR if on warfarin.
DailyMed/FDA (NIH/NLM) — approved Phytonadione label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c7ef968-2c76-4220-a9ec-3179d243c422
High doses of phytomenadione may precipitate haemolysis in patients with G6PD deficiency.
Use with caution in G6PD deficiency; monitor for signs of haemolysis.
EMC-UK (MHRA) — approved Phytomenadione SmPC: https://www.medicines.org.uk/emc/product/9755/smpc
Phytomenadione is used for prophylaxis of haemorrhagic disease of the newborn; it is safe at recommended doses.
Can be used in pregnancy when indicated (e.g. maternal vitamin K deficiency).
Excreted into breast milk; maternal supplementation is not problematic.
No specific additional contraception.
EMC-UK (MHRA) — approved Phytomenadione SmPC: https://www.medicines.org.uk/emc/product/9755/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Vitamin K1 — essential cofactor for the gamma-carboxylation of vitamin K-dependent clotting factors (II, VII, IX, X) and proteins C and S; specific antidote for coumarin-induced hypoprothrombinaemia.
Vitamin K acts as a cofactor for hepatic gamma-glutamyl carboxylase, converting the inactive precursors of factors II, VII, IX, X and proteins C/S into functional calcium-binding proteins (Gla domains) — required for coagulation.
Well absorbed intramuscularly (and orally as phytonadione); after administration, clotting factors (especially FVII, short half-life) begin to normalise within hours, with maximal effect ~12-24 h.
Virtually no free unmetabolised vitamin K appears in bile or urine; after absorption it initially concentrates in the liver, but the hepatic concentration declines rapidly; very little vitamin K accumulates in tissues.
Rapid but limited duration of action (hepatic reserves deplete within days); complete and sustained correction of coagulation depends on hepatic synthesis and continued replacement of the underlying cause.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
