My son who is 24 years old was prescribed ceftin (cefuroxime) for tonsillitis and has had diarrhea with blood for a while now. how long can that last?

Might be serious: Antibiotic related diarrhea can sometimes be a sign of a secondary infection in the bowel. This is particularly worrisome if the diarrhea is bloody. This type of infection is due to a bacteria commonly referred to as "c. Diff" and requires additionaly therapy. Your son should have this evaluated with proper laboratory testing.