Table 5.

Methadone maintenance dose and CYP2B6 and ABCB1 gene mutation relationships with R,S-methadone plasma concentration^{a, b}.

Variable	Regression coefficient (β)	95% CI	P value
Dose (mg)	0.0006	0.002–0.009	0.001*
CYP2B6 A785G
A/G, G/G (versus A/A)	0.44	0.049–0.839	0.03*
ABCB1 G2677T
G/T, T/T (versus G/G)	0.37	0.124–0.616	0.003*

^aR,S-Methadone concentration was natural-logarithmically transformed to achieve a normal distribution.

^bResults are from stepwise multiple linear regression analysis. Age, marital status, weight, current amphetamine use, treatment duration, drugs related to methadone-drug interactions, CYP2B6 G516T (*9), CYP2C19 G681A/C (*2), G636A (*3), C3402T (*17), ABCB1 C1236T, and C3435T were not significantly associated. Only variables significantly contributing to the models are displayed (variables selected using mixed stepwise regression); P value for model: <0.0001.