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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

From: Isobolographic analysis of the opioid-opioid interactions in a tonic and a phasic mouse model of induced nociceptive pain

Drugs

ED50(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

  1. *P < 0.05 compared with ED50 theoretical.