In vivo 19fluorine nuclear magnetic resonance spectroscopy was used to
measure the brain concentration of fluoxetine and norfluoxetine in five
patients with obsessive-compulsive disorder and three with major
depression. The mean brain:plasma ratio of the parent drug plus the
metabolite was significantly elevated to 2.6 (SD = 1.0) (95% confidence
interval = 1.9-3.3). This accumulation may have implications for
understanding both the therapeutic and the toxic effects of fluoxetine.