Warfarin Poisoning

Clinical assessment

Based on history of known or suspected ingestion (warfarin tablets or rodenticide). Clinical evidence of bleeding (often delayed). High index of suspicion needed, especially with unexplained bleeding or ingestion of unknown substance.

Investigations

• Prothrombin Time (PT) / International Normalized Ratio (INR): CRITICAL test. Measures extrinsic pathway clotting function, which is dependent on factors II, VII, X. INR will be elevated (prolonged PT). Obtain baseline INR and monitor serially. Degree of elevation indicates severity of anticoagulation.
• Complete Blood Count (CBC): Check Hemoglobin (Hb) and Hematocrit (Hct) for evidence of blood loss/anemia.
• Consider: Type and Cross-match (if significant bleeding or transfusion anticipated). Renal and Liver Function Tests.
• Imaging (CT head, abdominal CT) if internal bleeding (e.g., intracranial, retroperitoneal) suspected based on symptoms.

Diagnostic criteria

History of exposure + Elevated INR + Clinical signs of bleeding (or potential for bleeding).

Non-pharmacological management

• Stabilization: ABCDE approach. Address life-threatening bleeding immediately.
• GI Decontamination:
• - Activated Charcoal (Single dose): Give 50g (1g/kg child) orally/NGT if patient presents within 1-2 hours of ingestion. May reduce absorption.
• - Gastric Lavage: Generally not recommended due to delayed effects and risk.
• Supportive Care: IV fluids for volume resuscitation if significant bleeding/shock. Blood transfusion (Packed Red Blood Cells - PRBCs) if severe anemia or ongoing massive bleeding.
• Control active bleeding sites if possible (direct pressure).

Pharmacological treatment

• ANTIDOTE: Vitamin K1 (Phytomenadione): Essential for reversing warfarin effect by promoting synthesis of clotting factors. Effect is delayed (requires synthesis, takes hours).
• Dosing (based on INR and bleeding):
• - No significant bleeding, INR elevated: May hold warfarin (if therapeutic use), monitor INR closely. Consider low dose oral Vitamin K1 (e.g., 1-2.5mg) if INR very high.
• - Minor bleeding, any INR elevation OR No bleeding, INR significantly elevated (e.g., >5-10): Give Vitamin K1 1-5 mg orally (preferred if no major bleed) or slow IV (e.g., 1-2.5 mg). Monitor INR daily and repeat Vit K1 as needed.
• - Major bleeding (life-threatening): Immediate Reversal Needed. Give Vitamin K1 5-10 mg SLOW IV infusion (e.g., over 30 mins - risk of anaphylactoid reaction with rapid IV push). PLUS immediate clotting factor replacement:
• - Prothrombin Complex Concentrate (PCC) - 4-factor PCC (e.g., Kcentra, Octaplex) is preferred agent if available (contains factors II, VII, IX, X). Dose based on INR and weight.
• - Fresh Frozen Plasma (FFP): Use if PCC unavailable. Provides clotting factors but requires large volumes (risk of fluid overload) and takes time to thaw/infuse. Dose typically 10-15 mL/kg.
• Superwarfarin (Rodenticide) Poisoning: Requires much larger and prolonged doses of Vitamin K1 (oral or IV), often for weeks or months, guided by serial INR monitoring.
• Follow specific Ugandan treatment algorithms/guidelines (may differ based on local availability of PCC/FFP).

Monitoring

Serial INR monitoring is crucial to guide Vitamin K1 dosing and assess response (e.g., daily initially, then less frequently as INR stabilizes). Monitor for signs of ongoing or new bleeding. Monitor Hb/Hct. Monitor for adverse reactions to Vitamin K1 (esp. IV) or blood products.