Episode 226: Superwarfarin Toxicity

Toxicology & Pathophysiology

• Long-acting vitamin K antagonists (LA-VKAs), developed as potent rodenticides
• Examples: brodifacoum, bromadiolone, difenacoum, chlorophacinone
• Much more potent + far longer acting than warfarin
• MOA: inhibits VKORC1 → ↓ vitamin K recycling → impaired γ-carboxylation
• ↓ factors II, VII, IX, X + proteins C/S
• Highly lipophilic → extensive tissue/fat sequestration + slow redistribution
• Effect can persist weeks-months; occasionally much longer
• Not dialyzable
• Exposure: large acute ingestion OR repeated low-dose exposure
• Source may be unclear, concealed, or initially unknown

Presentation

• Often delayed + insidious
• Severe coagulopathy may precede obvious bleeding
• Early: epistaxis, gingival bleeding, bruising/ecchymoses, hematuria
• Classic clue: well-appearing pt + extraordinarily abnormal coagulation studies
• Severe bleeding: RP hemorrhage, ICH, spinal hemorrhage, tamponade, major GI/GU bleeding
• RP bleed → flank/back pain ± CVA tenderness

Labs & Diagnosis

• PT/INR: profoundly elevated, sometimes beyond assay range
• aPTT: may also be markedly prolonged with severe factor depletion
• CBC/plts: often initially preserved unless major blood loss/other process
• LFTs: often relatively normal
• Profound INR + no warfarin + preserved liver function → think superwarfarin
• CT based on bleeding site; CT A/P for suspected RP hemorrhage
• Confirm: specialized serum/blood testing for long-acting anticoagulants, typically chromatography/mass spec
• Do NOT delay resuscitation/treatment for confirmatory testing

Elevated INR: Differential

• Superwarfarin exposure
• Warfarin toxicity
• Severe vitamin K deficiency: malnutrition, malabsorption, prolonged abx
• Liver failure/cirrhosis
• DIC
• Acquired factor deficiency/inhibitor

Helpful discriminators

• Liver dz → abnormal hepatic profile/clinical context
• DIC → ↓ plts, ↓ fibrinogen, ↑ D-dimer
• No warfarin + massive INR + relatively normal LFTs/plts → superwarfarin rises on the differential

ED Management

Major/Life-Threatening Bleeding

• Goal: replace factors NOW + restore endogenous synthesis
• 4F-PCC = preferred factor replacement
  • Fast, predictable correction
  • Small volume
  • No thawing/type matching
• FFP if PCC unavailable
  • Slower + large volume/TACO risk
• Give IV vitamin K concurrently
• PCC = immediate bridge; vitamin K = sustained factor synthesis
• Recheck INR + clinical bleeding response
• Repeat PCC generally not routine; reassess before redosing

No Major Bleeding, Critical INR

• Vitamin K is primary therapy
• High-dose PO vitamin K often preferred when clinically stable
• Avoid unnecessary PCC/FFP if no major bleeding
• Serial INR monitoring essential

Poison Control

• Call early
• Helps with:
  • Confirmatory testing
  • Vitamin K dosing
  • Duration of therapy
  • Monitoring/taper strategy
  • Outpatient planning

The Long Game

• This is NOT standard warfarin toxicity
• Vitamin K requirements may persist for months
• Discharge only when bleeding controlled + clinically stable on oral regimen
• Close serial INR follow-up mandatory
• Slowly taper vitamin K under laboratory guidance
• Stopping too early → rebound INR elevation + recurrent bleeding

Take Home Points

1. Massive unexplained INR + relatively normal liver function → think superwarfarin
2. Major bleeding → 4F-PCC + IV vitamin K
3. Expect prolonged vitamin K therapy + meticulous INR follow-up