Table 1

Inhibitory properties of enantiomers of methadone and its metabolites and structural analogs of methadone on nicotine-stimulated⁸⁶Rb⁺ efflux from KXα3β4R2 cells

Drug	IC₅₀
	μM
(±)-Methadone	1.9 ± 0.2
(⁺)-Methadone	2.5 ± 0.2
(−)-Methadone	2.0 ± 0.3
(⁺)-EDDP	0.4 ± 0.2
(−)-EDDP^1-a	0.4 ± 0.1^1-a
(⁺)-EMDP	5.8 ± 1.0
(−)-EMDP	6.3 ± 0.7
Propoxyphene	2.7 ± 0.4
Norpropoxyphene	1.8 ± 0.1
LAAM	2.5 ± 0.4
Mecamylamine	1.1 ± 0.2

IC₅₀ values were calculated from inhibition curves in which⁸⁶Rb⁺ efflux was stimulated by 100 μM nicotine, as described under Experimental Procedures. Mecamylamine, a standard nAChR antagonist, was included for comparison. Data shown are the mean ± standard error of three to six independent measurements.

↵1-a The IC₅₀ value for (−)-EDDP is significantly lower than that for mecamylamine (p < 0.02).