I take 30 mgs of Avinza daily. There is an immediate release portion that kicks in within 30 minutes-2 hours depending on if you take it with food (I take it with food so the immediate release is more controlled and sustained...if I take it on an empty stomach I get sleepy and nauseous). The extended-release pellets are supposed to release at different intervals during the day (ie some at 2hrs, some at 4hrs, etc.) so that you sustain a steady blood level of morphine. Basically, you are getting short bursts in time intervals that keep your blood level as steady as possible.
As far as using phenergan, it is a great drug, but can make you very sleepy. It also potentiates the morphine and makes it stronger. I have both phenergan and another medication, called Reglan, on hand for nausea. I really like the Reglan because it doen't make you drowsy and it does not add to the side effects of the Avinza.
Good Luck!
txmomof3