Interaction between Mu and Delta Opioid Receptor Agonists in an Assay of Capsaicin-Induced Thermal Allodynia in Rhesus Monkeys

Table 1

ED50 values (95% confidence limits) in mg/kg for the antiallodynic effects of methadone, morphine, and nalbuphine administered alone or in combination with other drugs. Symbols indicate significantly different from mu agonist alone (*) or from 0.9 : 1 SNC80/methadone alone (†) as indicated by nonoverlapping confidence limits.

Treatment	ED50 (95%CL)
Methadone
Methadone alone	0.98 (0.48–1.97)
0.9 : 1 SNC80/methadone	0.34 (0.21–0.56)
0.9 : 1 SNC67/methadone	1.03 (0.27–3.31)
Methadone + 0.1 NTX	>10*
Methadone + 1.0 NTI	1.37 (0.22–3.61)
0.9 : 1 SNC80 methadone + 0.1 NTX	2.97 (2.09–4.86)^†
0.9 : 1 SNC80/methadone + 1.0 NTI	2.08 (0.98–5.52)^†
Morphine
Morphine alone	0.41 (0.14–1.60)
0.29 : 1 SNC80/morphine	0.38 (0.22–0.68)
Nalbuphine
Nalbuphine alone	0.15 (0.07–0.43)
3.6 : 1 SNC80/nalbuphine	0.08 (0.04–0.17)