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. 2014 Jul 15;21(1):62. doi: 10.1186/s12929-014-0062-6

Table 3.

Theoretical and experimental ED 50 values with 95% CL, and interaction index for the antinociceptive activity of the intraperitoneal coadministration of morphine with methadone, morphine with fentanyl, and morphine with tramadol, fentanyl with methadone, methadone with tramadol, and fentanyl with tramadol in the writhing test of mice

Drugs
ED 50 (95% CL)
Interaction index
  Theoretical Experimental  
Morphine/methadone
0.104(0.14-0.07)
0.023*(0.03-0.02)
0.226
Methadone/fentanyl
0.050(0.07-0.03)
0.019* (0.02-0.01)
0.387
Morphine/tramadol
2.014(3.55-1.14)
0.811* (1.05-0.64)
0.403
Morphine/fentanyl
0.070(0.10-0.05)
0.034* (0.06-0.02)
0.487
Methadone/tramadol
1.994(3.01-1.31)
1.032* (2.20-0.62)
0.518
Fentanyl/tramadol 1.960(2.88-1.32) 1.023* (1.68-0.70) 0.522

*P < 0.05 compared with ED50 theoretical.