A 5 year old male with no previous medical history is brought to the ER by his mother because he accidentally ingested a large dose of rat poison. He is conscious but appears quite agitated. On physical exam, he is found to have a blood pressure of 110/70 and a hea rate of 90. Labs are significant for an elevated PT but a normal PTT. The patient should be immediately treated with?

**Core Concept**
The patient likely ingested warfarin, a vitamin K antagonist that inhibits the production of clotting factors in the liver, leading to an isolated prolongation of the prothrombin time (PT) due to a deficiency of clotting factors II, VII, IX, and X.

**Why the Correct Answer is Right**
The patient's presentation with an elevated PT and normal partial thromboplastin time (PTT) suggests warfarin toxicity. The mechanism of warfarin involves the inhibition of vitamin K-dependent carboxylation of glutamic acid residues in the gamma-carboxyglutamic acid (Gla) domain of clotting factors II, VII, IX, and X. This carboxylation is necessary for the binding of calcium ions, which in turn allows these clotting factors to bind to phospholipid surfaces and facilitate coagulation. Warfarin's effect is most pronounced on the production of these clotting factors, leading to a selective prolongation of PT.

**Why Each Wrong Option is Incorrect**
**Option A:** Fresh frozen plasma (FFP) would be an incorrect choice because it contains all clotting factors, including those that are not affected by warfarin (such as factors VIII, XI, and XII). FFP would not selectively correct the PT prolongation caused by warfarin.
**Option B:** Platelet transfusion is not indicated in this scenario because the prolongation of PT is due to a deficiency of clotting factors, not thrombocytopenia.
**Option C:** Desmopressin would be an incorrect choice because it is used to treat bleeding disorders caused by von Willebrand disease or hemophilia A, which are not relevant in this scenario.
**Option D:** Cryoprecipitate is not the correct choice because it contains fibrinogen, factor VIII, and von Willebrand factor, but not the specific clotting factors affected by warfarin.

**Clinical Pearl / High-Yield Fact**
The treatment of warfarin toxicity involves the administration of vitamin K1 (phylloquinone) to restore the production of clotting factors. The dose and duration of vitamin K1 therapy depend on the severity of the PT prolongation and the presence of bleeding.

**Correct Answer:** C. Vitamin K1 (phylloquinone)

✓ Correct Answer: D. Vitamin K