Rationale: Although selective serotonin reuptake inhibitors (SSRIs) are widely used in the treatment of anxiety and depressive disorders, the occupancy of the serotonin reuptake transporter (SERT) achieved in humans at typical clinical doses by these agents remains poorly characterized.
Objective: The purpose of this study was to determine the occupancy of the SERT achieved in vivo by the SSRI paroxetine in social phobia patients at typical antianxiety doses.
Methods: Measures of SERT availability were obtained with positron emission tomography and the SERT radiotracer [(11)C](+)-McN 5652 in five patients with social phobia before and during treatment with paroxetine at usual therapeutic doses (20-40 mg per day).
Results: Occupancy of the SERT by paroxetine was high in all subjects and in all regions measured after 3-6 months of continuous treatment.
Conclusions: The results of this study in an anxiety disorder sample are consistent with previously reported results in a depressed sample and suggest that paroxetine at therapeutic doses achieves very high occupancy levels of the SERT.