CautionMarevan
Warfarin
Vitamin K antagonist
Teratogen — avoid 6–12/40. Used only for mechanical heart valves after careful counselling.
Oral
First-line for
- Mechanical heart valve (specialist only)
Mechanism
Inhibits vitamin K epoxide reductase → ↓ functional factors II, VII, IX, X and proteins C/S. Crosses placenta freely.
Warfarin embryopathy — “FACES”
- F — Facial dysmorphism (nasal hypoplasia)
- A — Atrophy of optic nerve
- C — Chondrodysplasia punctata
- E — Epiphyseal stippling
- S — Stunted growth
Dosing
- Target INR
- Depends on valve type
- Switch
- To LMWH 6–12/40 + from 36/40
Contraindications
- AbsolutePregnancy 6–12/40 (teratogen)
- AbsoluteActive bleeding
Side effects
- Bleeding
- Skin necrosis (early protein C drop)
- Purple toe syndrome
Fetal & maternal notes
- • Teratogenic 6–12/40 — embryopathy 5%.
- • Fetal intracranial haemorrhage risk in T3.
- • Safe in breastfeeding (not in milk).
Key interactions
NSAIDs
Avoid↑ INR + bleeding
Antibiotics
CautionVariable — recheck INR
Vitamin K
CautionAntagonises
Clinical pearls
- 💡 Counsel pre-conception: switch to LMWH before 6/40 if possible.
- 💡 Reversal: vitamin K + PCC (Beriplex).
Content last reviewed: REPLACE_ME (e.g. 2026-07)
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