Nitrofurantoin
"I had a bad reaction.  I started feeling worse and worse during the week, achy and flu-like. Then on the Saturday following the first dose on Monday, I started feeling feverish and by midnight my fever was 104.3.  I was unable to drive myself to an emergency room or critical care facility so I toughed it out and the fever finally broke about 4 AM and then the rashes started.  I broke out all over and it itched terribly.  By Monday I was able to drive the three blocks to see my Nurse Practitioner.  The worst part of the whole thing was that it didn't do anything for the bladder infection."