Relationship between in vivo potency (EC50,u) andin vitro receptor affinity (KI) for the three synthetic opioids
| Drug | KI,−Na (nM) | KI,+Na(nM) | Na-Shift3-a | EC50,u(nM) | EC50,u/KI,−Na |
|---|---|---|---|---|---|
| Alfentanil | 47.4 ± 6.6 | 906 ± 115 | 19.1 | 11.3 | 0.23 |
| Fentanyl | 8.6 ± 4.1 | 114 ± 17 | 13.3 | 2.02 | 0.25 |
| Sufentanil | 2.8 ± 0.2 | 7.9 ± 1.6 | 2.8 | 0.70 | 0.24 |
↵3-a Expressed as the ratio of the KIvalue in the presence and the absence of 100 mM NaCl, respectively.