Study of theThe durationlength and pattern of antidepressant use in the naturalistic setting can provideis an important insightsinput into how antidepressant use patterns compare to recommended depression treatment guidelines. TThe World Health Organization and consensus groups in the United Kingdom have , for example,established depression treatment guidelines recommendings at least four to ninenine months of antidepressant therapy beyond initial symptom resolution for depressive episodes. In light of the increased use of SSRIs, it is reasonable to evaluate whether differences exist among individual SSRIs in their use relative to guidelines. OBJECTIVE: The purpose of this study was to isassess the effects of initial SSRI antidepressant selection on the subsequent pattern and duration of antidepressant useacross drug types in actual clinical practice in the United States who had an indicator of a depression-related diagnosis on their insurance claims formssettingsgiven an initial drug selection. METHODS AND DATA: Logistic regression analysis of data from a large general practitioner medical records database (DINLINK) for the years 1992-97 was used to estimate the determinants of antidepressant drug use patterns for 6,007 patients with a "new" episode of antidepressant therapy who were prescribed one of three most often prescribed SSRIs: paroxetine, sertraline, or fluoxetineUsing an insurance claims database, we study antidepressant use patterns over a twelve month follow-up period for individual patients described as having depression and who initiated pharmacotherapy on tricyclic antidepressants, or the selective serotonin reuptake inhibitors (SSRIs) sertraline, paroxetine, or fluoxetine in an outpatient setting in the United States between 1990 and 1994. RESULTS: Patients who initiated therapy on sertraline or paroxetine were less likely than patients who initiated therapy on fluoxetine to have four or more 30-day prescriptions of their initial antidepressant within the first six months. The magnitude of these differences was greater for patients who initiated SSRI therapy between 1995 and 1997, as compared to 1992 through 1994. CONCLUSION: There is increasing evidence that antidepressant use patterns differ across TCAs and individual SSRIs in the actual clinical practice setting.The findings suggest that the particular SSRI selected is an important determinant of use consistent with current recommended depression treatment guidelines in primary care in the United Kingdom.