Can i mix seroquel (quetiapine) extended realese with the fast acting seroquel (quetiapine)??

Why?: You can but it does not make much sense to do so. Just wasting money essentially. One or the other.

Yes.: Yes, but talk to your doctor first. I'm not sure what your rationale for combining regular with the extended release, but I could think of a few reasons that might make sense for some patients (taking advantage of different half-lives at different times allowing for varying duration of effects depending on time of day etc).

Seroquel: Don't usually mix these. Only do this if prescribed this way by your prescriber.