Selective potentiation of opioid analgesia by nonsteroidal anti-inflammatory drugs

Opioids are often used in conjunction with nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of moderate to severe pain. In this study we have examined interactions between these two classes of drugs. NSAIDs are inactive in the radiant heat tail-flick test, an assay of moderate to severe pain in which opioids are effective. In this assay, ibuprofen potentiated the analgesic actions of hydrocodone and oxycodone, shifting their ED50 values by 2.5-fold and 4.6-fold despite its inactivity when given alone. These opioid/NSAID interactions were dependent upon both the opioid and the NSAID. Neither aspirin nor ketorolac influenced hydrocodone actions in this model and ibuprofen did not potentiate fentanyl or morphine analgesia. Together, these studies demonstrate potent interactions between selected combinations of opioids and NSAIDS and may help explain the clinical utility of combinations. However, the findings also illustrate differences between the drugs within each class.