These are alpha agoinst which on topical application as dilute solution (0.05-0.1% ) produce local vascocostruction.
The imidazoline compounds- naphazoline, xylometazoline and oxymetazoline are relatively selective a2 agoinst like chlonidine.
They have a longer duration of action than emphedrine. After congestion is claimed to be less than the ephiderine or phenylephrine. May cause initial stinging sensation