Phenytoin
"After about 8 days of being on Dilantin, I had a horrible allergic reaction. I woke up at like 4:30 with unbearably itchy hives that literally covered my whole body....face, shoulders, chest, stomach, back, buttocks & legs....even on the backs of my hands and feet, with a few spots on the palm of my hand. It sucked, needless to say. It also made me really tired all day, even though I'd take it at night. I'm now starting on KEPPRA. Hope it works."