. 2019 Nov;371(2):409–415. doi: 10.1124/jpet.118.256115

TABLE 5.

Nalmefene and naloxone: a comparison of affinities at μ opioid receptors and pharmacokinetic properties following intranasal administration

Parameter	Nalmefene	Naloxone
K_i (nM)	1.0^a	5.4^a
t_1/2 (h)	7.11^b	2.08^c
T_max (h)	0.25^b	0.5^c
C_max (ng/ml)	4.45^b	4.83^c

^{^a}

K_i values were estimated using [³H]alvimopan binding to cloned human μ opioid receptors (Cassel et al., 2005). The ∼5-fold higher affinity of nalmefene compared with naloxone is consistent with both K_i values obtained (0.13 and 0.62 nM, respectively) using [³H]DAMGO as a radioligand in monkey brain membranes (Emmerson et al., 1994) and pA₂ values of 9.38 and 8.51, respectively, in functional assays using guinea pig ileum and mouse vas deferens (Toll et al., 1998).

^{^b}

Data from Table 2.

^{^c}

Data from https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/208411lbl.pdf.