There are two rare, but severe, side effects with Erbitux and that is an allergic reaction, and heart attack, which mostly occur the first or 2nd infusion in a small percentage of people. Benadryl is given to help with the allergic reaction, and staff monitor you closely, and you are to report anything out of the ordinary. The other which is expected, and sign of the Erbitux working is the rash, which is managed by antibiotics. They say for about 5% of head and neck cancer patients this drug doesn't work due to the Kras gene mutation, but there is no assay test to find this out unlike for colorectal cancer, which blood test is given before starting to see if one is a candidate or not.

http://www.erbitux.com/index.aspx