-Both are highly anti-cholinergic and similar MOA -One is OTC the other is prescription only -Both are frequently used in psychiatry. A) hydroxyzine for anxiety, sometimes sleep. B) diphenhydramine for EPS ppx typically. -Both have IM formulations, though IM hydroxyzine doesn’t seem to ever be used in clinical practice (why has it never caught on aside from maybe cost?). -hydroxyzine has a longer half life -an unreliable source (the only I could find) says hydroxyzine is more centrally acting. Isn’t this a good thing to avoid off target receptor activity?
So why isn’t hydroxyzine ever used for EPS ppx? Or combined with haldol/Ativan to treat agitation? Why is it not OTC? Etc. Basically what is the difference between these two drugs??