TABLE 1

Parameters used for correlation of in vitro, preclinical, and clinical data

Parameter	Alfentanil	Fentanyl	Loperamide	Meperidine	Methadone	Morphine	Sufentanil
In vitro K_i (nM)^a	19	1.6	0.50^b	193	2.2	5.7	0.10
Mouse ED₅₀ (mg/kg)	0.079	0.020	36	3.2	2.2	0.94	0.00041
Mouse f_u,plasma	0.26	0.17^c	0.029	0.36	0.15^c	0.50^c	0.054^c
Mouse f_u,brain	0.33	0.070^c	0.0047	0.13	0.029^c	0.41^c	0.034^c
Human plasma EC₅₀ (nM)^d	1337	24	N.A.	6034^e	1151	195	1.8
Human equipotent i.v. dose (mg)^f	0.75	0.10	N.A.	90	8.75	10	0.015
Human t_1/2,Ke0 (min)^d	1.0	5.8	N.A.		12	178	6.2
Human f_u,plasma	0.079^g	0.156^g		0.35^e	0.125^h	0.75ⁱ	0.075^g

N.A., not available.
↵ a Leysen et al. (1983).
↵ b Terenius (1975).
↵ c Kalvass et al. (2007a).
↵ d Average from EEG power spectrum analysis, analgesia (cancer pain), pain tolerance, and/or postoperative analgesia (Lotsch, 2005).
↵ e Unbound potency of meperidine is 20 time less than alfentanil (Kurz et al., 1997).
↵ f Wood and Alastair (1990).
↵ g Meuldermans et al. (1982).
↵ h Inturrisi et al. (1987).
↵ i Glare and Walsh (1991).