it doesnt really work like hydromorphone to hydroxyine ratio lol, you are making things too difficult.
take 50mgs hydroxyzine 20-30mins before and then do your dilaudid. it is really not that important about when you take the vistaril. the best is to take it before, but you can take it with, or after... it doesnt potentiate the dilaudid, but it will synergize with the hydromorphone a little. it will take away any pruritis and sedate you a little it will also help with nausea.. nothing really special