It is demerol and phenergan to prevent nausea and increase it's effectiveness. Demerol is another med that is nowhere near as effective orally as it is when used IM or IV. Its rarely used in pain management because long term use causes a buid up of a toxic metabolites and can cause seizures. 150 mgs of oral demerol is roughly equal to 10 mgs of oxycodone.
For those alergic to morphine and codiene and the more common synthetics like hydrocodone and oxycodone it is a short term alternative for post op or procedure pain.
Good luck, Dave