Table 2.

Regression equations describing relationships between trough total plasma concentrations (TPC) of (RS)-, (R)- and (S)-methadone and significant covariates

TPC of (RS)-methadone = 540.5 + (2.9 × dose) + (−1.5 × DA) + (−4.7 × CYP3AA) + (−85.05 × AM)

TPC of (R)-methadone = 238.53 + (1.79 × dose) + (−0.81 × DA) + (−2.41 × CYP3AA)

TPC of (S)-methadone = 263.11 + (1.26 × dose) + (−0.65 × DA) + (−2.06 × CYP3AA (−53.38 × AM)

Dose, dose of methadone (mg); DA, duration of addiction before starting methadone maintenance therapy (month); CYP3AA, CYP3A activity [as measured by midazolam oral clearance (l h⁻¹)]; AM, abuse of morphine (positive = 1, negative = 0).