Levaquin I started taking Levaquin 500 mg. for a 5 day period for swollen glands and sinusitis. The first day did not bother me. However, the second day was awful. I took the pill at noon like I had done the day before and I went to bed around 10:30 PM. Next thing I know I have severe cramping and diarrhea. This lasted from midnight until 3:00 AM or so. Have not taken this since. I'm glad I looked at this site because I was thinking I had a 24 hour bug and was going to take my third day dosage. FDA needs to know about these severe side affects. I am going to inform them.