Effectiveness and Safety of Methadone Versus Placebo for the Control of Neuropathic Pain in Different Etiologies

The intervention with the active drug (methadone) will start with the dose of 1 tablet (5 mg) twice a day (every 12 hours) and titrated on subsequent visits up to the maximum dose of 6 tablets a day (totaling 30 mg divided into 2 daily doses to facilitate therapeutic adherence).

In this arm patients will take placebo tablets (the same number, color and physical aspects as the methadone tablets).