I don't take plegridy but I do Copaxone injections.... The nurse said hitting a vein causes a rush of the meds through your system and may cause a heart attack like feeling. She said it would only last 15 mins causes heart racing trouble breathing but goes away. She said it passes and won't cause harm but always avoid the vein as much as possible. I'm not sure plegridy causes the same reaction but, something to watch for and know it will pass after 15 mins.