Rationale: One of the major problems in methadone maintenance treatment is to find optimal individual doses for the patients.
Objective: The present study investigated whether the use of rating scales together with enantioselective analysis of l-methadone might facilitate dose adjustments in a clinical situation.
Methods: Rating scales were used to evaluate subjective and objective signs of well-being in relation to plasma methadone concentrations in two groups of patients receiving methadone maintenance treatment. The first group (n = 25) was well-adjusted according to clinical observations and were satisfied with their methadone doses (86.2+/-4.3 mg). The second group (n = 25) was in need of the methadone dose adjustment; they complained of low dosing, despite a dose level of 69.2+/-4.0 mg/day.
Results: Results indicated a significant correlation between dose and methadone concentration among dissatisfied patients only. The trough levels of d,l-methadone and l-methadone, as well as their elimination rates, were similar in the two groups of patients. There was a variable predominance of l- over d-methadone in plasma (ratio approximate to 1.2; range 0.7-3.6). Illicit use of drugs by the patients was related to the methadone dose and to satisfaction with the dose received. Increased illicit drug use among dissatisfied patients was successfully eliminated by raising the methadone dose. Subjective and objective ratings of the satisfied patients were quite stable throughout the evaluation period, whereas the ratings of the dissatisfied patients were unstable. These patients seemed to be more sensitive to low trough levels of methadone than the satisfied patients. Associations between the subjective and objective ratings and plasma methadone, along with background characteristics, were characterized by multiple regression analyses. The plasma concentrations of l-methadone were one of the most important explanatory variables in these analyses. Associations between well-being and methadone concentrations in plasma were stronger for l-methadone than for d,l-methadone.
Conclusions: Selective measurements of the active isomer and the use of rating scales should be of clinical value when monitoring methadone maintenance treatment patients.