Effects of combined opioids on pain and mood in mammals.

The authors review the opioid literature for evidence of increased analgesia and reduced adverse side effects by combining mu-opioid-receptor (MOR) agonists, kappa-opioid-receptor (KOR) agonists, and nonselective low-dose-opioid antagonists (LD-Ant). We tested fentanyl (MOR agonist) and spiradoline (KOR agonist), singly and combined, against somatic and visceral pain models. Combined agonists induced additive analgesia in somatic pain and synergistic analgesia in visceral pain.

Antinociceptive interactions of micro- and kappa-opioid agonists in the colorectal distension assay in rats.

Interactions of opioid agonists, fentanyl and oxymorphone (micro-selective) and spiradoline and enadoline(kappa-selective), were examined for additive, sub-additive, or supra-additive antinociception in the colorectal distension (CRD) assay. Single-dose values (mg/kg, 0.006-0.