A 2-year-old boy is brought in by his mother because of the bloody stool after ingestion of unknown amount of rat poison (coumarin based). He is admitted and treated with fresh frozen plasma and vitamin K after his prothrombin time (PT) was found to be prolonged. What is the reason for bloody stool in this case?

Answer: c) Coumarin is antagonizing vitamin K reductase necessary for production of factors II, VII, IX and X* Vitamin K is necessary for production of factors II, VII, IX, and X. Coumarin will antagonize vitamin K reductase and can result in the bloody stool after poisoning* Irritation of bowels is possible, but it wouldn't cause bleeding.* DIC is not caused by coumarin based poisons.