The FDA is warning that the antiseizure medicines can cause a rare but serious reaction, called Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), that can be life-threatening if not diagnosed and treated quickly.

http://www.fda.gov/safety/medical-product-safety-information/antiseizure-medicines-keppra-keppra-xr-elepsia-xr-spritam-levetiracetam-and-onfi-sympazan-clobazam