In vivo profiling of seven common opioids for antinociception, constipation and respiratory depression: no two opioids have the same profile

Background and PurposeFor patients experiencing inadequate analgesia and intolerable opioid-related side effects on one strong opioid analgesic, pain relief with acceptable tolerability is often achieved by rotation to a second strong opioid. These observations suggest subtle pharmacodynamic differences between opioids in vivo. This study in rats was designed to assess differences between opioids in their in vivo profiles.