3 year old just seen at the er last night broke out in hives dont know why she has a viral infection also. how many hours apart can i give benadryl (diphenhydramine)?

Rash with a virus: It is common, especially with children, to get a rash with certain viruses. The rash tends to get better in a few days. Treatment of an itchy rash can be with antihistamines. I prefer the long-acting, non-sedating antihistamines like ceterezine (Zyrtec) or loratadine (Claritin) in kids, which is taken once a day. Diphenhydramine (Benadryl) can be used every 4 to 6 hours, but it makes you sleepy.