U01.01.075 Vitamin K

Alternate Names: Phytomenadione, Phylloquinone, Phytonadione, Menaquinone
Function:
- Vitamin K is activated by epoxide reductase to its reduced form.
- The reduced form acts as a cofactor for the γ-carboxylation of glutamic acid residues on various proteins involved in blood clotting.
- It is synthesized by intestinal flora.
- Mnemonic: K is for Koagulation — Vitamin K is crucial for the maturation of clotting factors II, VII, IX, X, and proteins C and S.
- Warfarin inhibits the vitamin K–dependent synthesis of these clotting factors and proteins.

Clotting Factor	Role	Vitamin K Dependency
Factor II (Prothrombin)	Critical for blood coagulation	Yes
Factor VII	Activates clotting cascade	Yes
Factor IX	Essential for clot formation	Yes
Factor X	Final step in clot formation	Yes
Protein C & S	Regulate clot formation	Yes

Symptoms:
- Neonatal hemorrhage
- Prolonged Prothrombin Time (PT) and activated Partial Thromboplastin Time (aPTT), but normal bleeding time.
- In neonates, this occurs because their intestines are sterile and unable to synthesize vitamin K.
Risk Factors:
- Prolonged use of broad-spectrum antibiotics: These can disrupt intestinal flora, impairing vitamin K synthesis.
- Breast milk: Vitamin K is not present in significant amounts in breast milk, which is why neonates receive a vitamin K injection at birth to prevent hemorrhagic disease of the newborn.

Mnemonic: Vitamin K = Koagulation.
Warfarin inhibits the vitamin K–dependent synthesis of clotting factors.
Deficiency Symptoms: Neonatal hemorrhage, prolonged PT/aPTT, normal bleeding time.
Sources: Synthesized by intestinal flora, not present in breast milk.
Prevention: Neonates receive vitamin K injection to prevent hemorrhagic disease of the newborn.

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