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Answers and Discussion

Case #10 -- Warfarin Toxicity

Answers and Discussions to the Questions:

Why is warfarin toxic or how does it work?

Warfarin (as well as other coumarins) is a vitamin K antagonist. It inhibits vitamin K epoxide reductase, which in turn inhibits the activation of vitamin K. Vitamin K is necessary for the synthesis of coagulation factors II, VII, IX and X in the liver. Lack of clotting factors leads to coagulopathy, resulting in hemorrhage.

What emergency treatments should be started for "Sippsy"?

A blood transfusion should be given. A plasma transfusion can also be given for added clotting factors. Avoid jugular catheters with any coagulopathy! Because of the dyspnea, oxygen supplementation is warranted. Vitamin K injections should be started. DO NOT GIVE IM INJECTIONS! Give the Vitamin K SQ (2-5 mg/kg for a couple doses, then switch to oral dose).

What do you think should be done about the dyspnea and decreased lung sounds?

A chest tap should be done, especially if the dyspnea worsens. Thoracocentesis was performed on "Sippsy" --- 385 ml of blood was removed, filtered, and auto-transfused after "Sippsy" received the first unit of blood and a unit of plasma.

What laboratory tests can be used to monitor platelet function and progress of your treatment of the coagulopathy?

The tests include activated clotting time (ACT), prothrombin time (PT), and activated partial thromboplastin time (APTT). When "Sippsy" was first admitted, her ACT was 240 seconds (normal = 90-120 seconds); PT was 17.6 seconds (normal = 7.5-10.5 seconds); APTT was 59.0 seconds (normal = 10.5-16.5 seconds). After 2 days of treatment, "Sippsy's" ACT was down to 115 seconds; PT was 8.7 seconds; APTT was 15.6 seconds.

What important medication would you send home with the patient upon dismissal?

Vitamin K therapy needs to continue for at least 7-14 days. Longer-acting rodenticides may require treatment up to a month (like brodifacoums and bromadiolones). Oral vitamin K dose is 2-5 mg/kg per day.

Follow-Up: "Sippsy" was sent home after 2 days of in-hospital treatment. The owners continued to give her oral vitamin K. She was doing great at her 2-week recheck. Blood values have all returned to normal.

Warfarin Toxicity Pearls

Warfarin (coumarins) inhibits vitamin K, thereby inhibiting clotting factor function; this results in hemorrhage, most commonly in the chest or abdomen.
Blood transfusions and vitamin K supplementation are necessary treatments.
Avoid IM injections or anything that may cause bruising to the patient!
Clotting factor and platelet function can be monitored by ACT's, PT's and APTT's.