Antiallodynic and antinociceptive potency of loperamide and fentanyl (n = 4, unless otherwise stated)


Antiallodynia ED10″ (95% CL)a with Topical Capsaicin

Antinociception ED10′ (95% CL)b without Topical Capsaicin, 48°C
Loperamide 0.18 (0.05-0.6) 0.59 (0.25-1.4) Inactive to 1 mg/kg
0.0078 (0.0014-0.042)
0.012 (0.0022-0.063)
0.014 (0.0017-0.11)
  • 95% CL, 95% confidence limits.

  • a ED10′ values are in mg/kg, measured at the time of peak capsaicin-induced allodynia (i.e., 30 min after topical capsaicin removal).

  • b ED10′ values were determined, for each opioid agonist, at a time equivalent to that in the allodynia studies (i.e., 60 min and 45 min after loperamide and fentanyl injection, respectively).

  • c All fentanyl ED10′ values are based on n = 3. The fourth subject did not attain the 10-s level of effect in any fentanyl condition, up to the largest fentanyl dose studied. Larger fentanyl doses could not be evaluated in this subject, due to the occurrence of respiratory depression.