- All the volunteers have to be phenotyped as CYP2D6 extensive metabolizer (EM) by a "tramadol test": the volunteer ingest 50 mg tramadol and all urine is collected fore 8 hours. By a HPLC method the metabolic ratio (MR) of (-)-M1/(+)-M1 is determined in the urine. Volunteers with a MR-ratio smaller than 2 is defined as CYP2D6 EM's