Vitamin K

Endogenous Vitamin K

  • Vitamin – an organic substance which:
    • Cannot be produced by the body
    • Must be obtained exogenously
    • Required only in small amounts
    • Essential for survival
  • Vit K = fat soluble vitamin
  • Reduced Vit K is an essential co-factor for γ-CARBOXYLATION of precursors to allow them to bind Ca2+ in:
    1. Factors II, VII, IX, X → deficiency of Vit K/warfarin use inhibits EPOXIDE REDUCTASE which will ↑PT
    2. Protein C & S → provides anti-thrombotic activity by inhibiting Va & VIII
    3. Osteocalcin → produced by osteoblases & participates in bone mineralisation → Vit K deficiency can lead to osteoporosis
    4. Haemorrhagic disease of Newborn → Vit K does not cross placenta & stored clotting factors in infants are low → ∴require Vit K injections after birth

Vitamin K Absorption

  • Large amounts made by bacteria in colon → but not absorbed because absorption is in terminal ileum where bile salts are present
  • Diet → green leafy veg + some meats + bile salts

→ Absorbed in terminal ileum

Factors Affecting Absorption

  1. Dietary intake
  2. Production by GM+ bac in GI tract → inhibited by a/b use
  3. Impaired GI absorption
    • Obstructive biliary disease/absence bile salts
    • R/O T. Ileum (Curtin’s)
    • Use of cholestyramine which ↓fat absorption
    • ↓transit time 2° drugs (metoclopramide) or disease (diarrhoea)
  4. Vit K liver stress
    • ↓stores = ↑absorption

Exogenous Vitamin K

Chemical

Phylloquinone

Use

Correction of INR

Presentation

Tablets 10mg

Vials; 2mg in 0.2ml and 10mg in 1ml

Dose

0.5-1mg repeated as necessary

Route

IV/PO

Onset

IV – maximal effect 6-12h

PO – maximal effect 12-24h

DoA

Clotting factor life span

MoA

Essential co-factor for γ-CARBOXYLATION

PD

Aids haemostasis

PK

A

PO requires bile salts for administration

D

M

E

No unmetabolized vitamin K appears in bile/urine

Adverse Effects

Disrupts re-anticoagulation in long term

Anaphylactoid reactions

Dyspnoea