Orphenadrine
"I received 60mg of norflex inter-muscular injection due to a pulled muscle in my shoulder blade around 3pm. About half an hour of receiving the shot I was very sleepy after getting home and slept for 6 hours, when I woke I had hives all over my body and went to the ER, where they gave me IV Benadryl and IV Pepcid ( some kind of steroid ) the rash dimmed a little so they sent me home with prescribed Epi pens, Benadryl, and a steroid.  Got home around midnight and went to sleep after taking my meds, when I woke the next morning I was covered in hives again but twice as many, so I went back to the ER when they told me this could last up to 5 days. I'm on day 3 now my entire body feels all bruised with itchy hives. I'm not allergic to anything."