Eligible patients , who were taking a strong opioid analgesic and had a mean pain intensity score < 4 during the 3 days prior to randomization ( adequate pain control on previous strong opioid ) , were randomized ( 1:1 ) to receive twice-daily treatment with tapentadol ER ( 100-500 mg/day ) or morphine sustained release ( SR ; 20-140 mg/day ; reference for assay sensitivity ) .