Venous blood sampling times were 0 (prior to dosing),2,4,6,8,10,12,16,20,24,30,36,42,and 48 hours after each Dilaudid SR administration. LC/MS/MS (Liquid Chromatography/Mass Spectroscopy/Mass Spectroscopy)techniques were employed for the analysis of plasma for hydromorphone concentration. Each patient randomly received orally-administered treatments of single dose of Dilaudid SR 16mg; under fasting conditions without the naltrexone block; under fed conditions without naltrexone block; under fasting conditions with naltrexone 50mg block (3 oral doses of 50mg naltrexone HCL each administered 12 hours prior to, at the time of, and 12 hours after hydromorphone administration); 7-day washout period between dosing phases.