Methadone is used as a maintenance treatment for opiate addiction. A linear relationship with a good correlation coefficient (n=31, r=0.82, P<.001) has been calculated between methadone dose and methadone concentrations in plasma.1 Methadone is marketed as a mixture (50:50) of 2 enantiomers called (R)-methadone and (S)-methadone, but (R)-methadone accounts for nearly all of the opioid effects of racemic methadone.2 We have developed a stereospecific analytical method that allows measurement of the concentrations of (R)-methadone and (S)-methadone.3 It was used to determine the (R)-methadone and (S)-methadone trough concentrations in the serum or plasma samples from 50 addicts receiving racemic methadone therapy in steady-state conditions.
Eap CB, Bertschy G, Baumann P, Finkbeiner T, Gastpar M, Scherbaum N. High Interindividual Variability of Methadone Enantiomer Blood Levels to Dose Ratios. Arch Gen Psychiatry. 1998;55(1):89-90. doi: