I've been taking oxycontine 40mg 2x a day for about 6 months for severe pain and they aren't working anymore .So, my doctor wrote a perscription for morphine sulfate er 40mg 2x a day .Is this equal or is there a percentage from one to the other ?? I know there isn't a 40 mg .They either come 15,30,60,100,200 what would the equal be ??