When my son was little he had a bizarre reaction to liguid prednisone, and his ped gave us a compounded/liquid form of . . . Baby Valium, I guess. But there are certainly things like Benadryl, etc. Do you have a regular psychiatrist? Would your GP or pediatrician prescribe some low dose soother?
There is also 2-point restraint, and 4-point restraint taught in the Management of Assaultive Behavior. It's a way of holding which keeps the child safe, as well as yourself, while you wait for her/him to deescalate.
I'm so sorry it's so tough. I know from experience there's something so heart-hurting about violence or meanness in your child.
Stay strong :-)