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Essentials of Diagnosis
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General Considerations
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Warfarin and related compounds (including ingredients of many commercial rodenticides) inhibit the normal clotting system by blocking hepatic synthesis of vitamin K–dependent clotting factors
Half-life of the "superwarfarins" (such as brodifacoum, difenacoum and related compounds) used as rodenticides can be weeks or longer
Direct-acting oral anticoagulants
Dabigatran (direct thrombin inhibitor)
Apixaban, betrixaban, edoxaban, and rivaroxaban (factor Xa inhibitors)
Some of these, especially dabigatran, are largely eliminated by the kidney and may accumulate in patients with kidney disease
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Differential Diagnosis
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Liver disease
Hemophilia
Aspirin overdose
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The PT is increased within 12–24 h (peak 36–48 h) after an overdose of warfarin or superwarfarins but is not as predictably abnormal after overdose of dabigatran or rivaroxaban
After ingestion of brodifacoum, difenacoum, and related rodenticides (even after a single dose), inhibition of clotting factor synthesis may persist for several weeks or even months
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Diagnostic Procedures
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Emergency and supportive measures
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Discontinue the drug at the first sign of gross bleeding
Determine the PT
Note: dabigatran, apixaban, betrixaban, edoxaban, and rivaroxaban do not predictably alter the PT; however, a normal INR suggests no significant toxicity
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If the PT is elevated, give phytonadione (vitamin K1), 10–25 mg orally, and increase the dose as needed to restore the PT to normal
Do not treat prophylactically—wait for the evidence of anticoagulation (elevated PT)
Give fresh-frozen plasma, prothrombin complex concentrate, or activated Factor VII as needed to rapidly correct the coagulation factor deficit if there is serious bleeding
If the patient has been receiving anticoagulation therapy long-term for a medical indication (eg, prosthetic heart valve), give much smaller doses of vitamin K (1 mg orally) and fresh-frozen plasma (or both) to titrate to the desired PT
If the patient has ingested brodifacoum or a related superwarfarin, prolonged observation (over weeks) and repeated administration of large doses of vitamin K (as high as 200 mg/day) may be required
Vitamin K is not effective for ...