Hello, can you give me some more information?
Is your son having diarrhea? What is the consistency and color of his stools. Does he have pain when he has a bowel movement? How much blood is there?
If he is not having diarrhea and having no pain with his bowel movements, he may have some irritation of his colon. This can be a virus of some type. The ibuprofen usually irritates the stomach and can cause bleeding in rare circumstances, but usually with excess use. Blood from the stomach once passed in the stool becomes dark black looking and not red.
If the cats are healthy and regularly dewormed, I am less concerned about this.
He could have an anal fissure (crack in the lining of the anus -- usually from stool irritation) and this may cause a small amount of bleeding.
Keep an eye on him. If the bleeding does not resolve in a couple of days, I recommend having him evaluated again (and certainly if he develops any other symptoms).
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