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Vitamin K Antagonist Pregnancy: D

Warfarin

Brand names: Coumadin, Marevan

Adult dose

Dose: Induction: 10 mg day 1 (or 5 mg if elderly/comorbid); maintenance dose titrated to INR
Route: oral
Frequency: once daily (same time each evening)
Max: Titrated to INR target
INR targets: AF/VTE: 2–3; mechanical mitral valve: 3–4; if 2 INR values outside range at same appointment → refer to anticoagulation service

Paediatric dose

Dose: 0.2 mg/kg
Route: oral
Frequency: once daily
Max: 10 mg loading
Concentration: 1 mg, 3 mg, 5 mg tablets mg/ml
Specialist use; INR monitoring more frequent in children due to dietary variability; vitamin K intake consistency important

Dose adjustments

Renal

No dose adjustment required (but increased bleeding risk in CKD)

Hepatic

Increased sensitivity — significant liver disease greatly increases INR

Paediatric weight-based calculator

Specialist use; INR monitoring more frequent in children due to dietary variability; vitamin K intake consistency important

Clinical pearls

  • Yellow warfarin 5 mg, brown 1 mg, blue 3 mg — standard UK colour coding
  • Dietary consistency: advise consistent vitamin K intake (leafy green vegetables) — not avoidance
  • Reversal: vitamin K oral/IV for over-anticoagulation; 4-factor PCC (Beriplex/Octaplex) for urgent reversal

Contraindications

  • Pregnancy first trimester (warfarin embryopathy)
  • Active bleeding
  • Recent surgery/trauma with high bleeding risk
  • Unsupervised patient unable to comply with monitoring

Side effects

  • Haemorrhage (all sites)
  • Skin necrosis (protein C/S deficiency — early initiation without heparin cover)
  • Purple toe syndrome (cholesterol embolism)
  • Teratogenicity

Interactions

  • Hundreds of interactions — check every new drug; amiodarone/fluconazole/NSAIDs increase INR; rifampicin/carbamazepine reduce INR
  • Alcohol: binge drinking increases INR

Monitoring

  • INR (initially daily/alternate days until stable, then 8–12 weekly)
  • MHRA yellow anticoagulant booklet issued to all patients

Reference: BNFc; BNF 86; BCSH guidelines; NICE NG196. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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