Azithromycin
"My 90-year-old mother was given the 6 tablet blister card/pack, and she took the first dose (2-250 mgs) as per her physician ordered at 3:30 p.m.   Within 4 hours she developed abdominal pain, overnight she was not able to urinate and that continued until 10:30 a.m. the next day.   We ended in the emergency room by 2:30 p.m. Subsequently, my mother had the worst case of diarrhea that I have ever seen, which was also caused by the antibiotic Levaquin. I have now added both of these drugs to her allergic list."