My Son Has Colon Cancer With Liver Involvement. He Is

My son has colon cancer with liver involvement. He is being treated with a cocktail of chemos. He experiences pain from the liver. They had him on oxicotin (20 mg slow 12 hour release) and he was psychotic so they stopped that. He is still taking oxicodine (5 mg, every 3 hours) and zanax for anxiety, and he is unable to eat or drink because he is so drowsy.. then he gets dehydrated..

help! should he be on oxicodine -- how different is that from oxicotin??
Is there any other pain med that can be substituted. He is 41 with no former illness or health problems and there is no colon cancer in the family

thank you