allergic reaction

My son has been diagnosed with Toxic Epidermal Necrolysis. I am wondering if there are any cases of a patient who has had an allergic reaction to Benadryl as serious as this? I gave him Benadryl for a few days for hives and he got worse over the course of four days.I have heard of one other case similar but would like more info please. My son is very sick and I would like to know what from and what to avoid in the future.

Thank You for your time, Treena Wunder