To assess the indications, prescription patterns, effectiveness, and side effects of oral methadone for the treatment of chronic noncancer pain.
We conducted searches of several electronic databases, textbooks and reference lists for controlled or uncontrolled studies in humans. Effectiveness was assessed using a dichotomous classification of “meaningful” versus “nonmeaningful” outcomes.
Twenty-one papers (1 small randomized trial, 13 case reports, and 7 case series) involving 545 patients with multiple noncancer pain conditions were included. In half of the patients, no specific diagnosis was reported. Methadone was administered primarily when previous opioid treatment was ineffective or produced intolerable side effects. Starting dose ranged from 0.2 to 80 mg/day and maximum dose ranged from 20 to 930 mg/day. Pain outcomes were meaningful in 59% of the patients in the uncontrolled studies. The randomized trial demonstrated a statistically significant improvement in pain for methadone (20 mg/day) compared to placebo. Side effects were considered minor.
Oral methadone is used for various noncancer pain syndromes, at different settings and with no prescription pattern that could be identifiable. Starting, maintenance, and maximum doses showed great variability. The figure of 59% effectiveness of methadone should be interpreted very cautiously, as it seems overrated due to the poor quality of the uncontrolled studies and their tendency to report positive results. The utilization of oral methadone for noncancer pain is based on primarily uncontrolled literature. Well-designed controlled trials may provide more accurate information on the drug's efficiency in pain syndromes and in particular neuropathic pain.