A while ago, I became very interested in the nasal route, as a delivery route to the brain. There is a channel in the nose, which by-passes the Blood brain barrier, and leads directly into the brain. It is called something like the veremonasal channel.
It is the reason why many addicts take thier drugs by snorting them, they get an instant high. Why does a smoker get an instant hit from his nicotine? He doesn't have to wait an hour for it to go via the bloodstream. It goes immediaterly to the brain through the nasal channel.
A couple of pharma companies investigated a nasal spray of levodopa,among them, a UK company called Brittania. I corresponded with them, but they eventually stopped the research. I don't know of any work going on now on this route.
Ron