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Guidelines for antidepressant drug therapy recommend continuing treatment for several months, even after recovery. Premature termination of medication is viewed as a significant reason for chronicity in depressive disorders. To study the scope and type of this problem, routine treatment cases must be observed in sufficient numbers. In four subsequent drug utilization observation studies, the time course and reasons for early termination (i.e., during the first weeks of fluoxetine treatment for depression) were investigated in (1) 15,601 patients of 4,696 general practitioners; (2) 2,401 patients of all ages treated by 479 neuropsychiatrists from 1990 to 1991; (3) 757 patients of all ages treated by 213 neuropsychiatrists from 1992 to 1993; and (4) in 977 geriatric subjects treated by 216 neuropsychiatrists. In study 1, treatment was terminated during the first 10 weeks in 32.9% of cases; in study 2, in 48.0%; in study C, in 31.2%; and in study D, in 31.0%. When treatment was discontinued because of adverse events, the median of treatment duration was approximately 15 days; in cases of clinical deterioration, 20 days; in cases of poor response, 40 days; and when the reason was good response, the median of treatment duration was approximately 43 days. This is the largest field study on early termination of antidepressant treatment available to date. The consistency of results, which were collected from a large number of patients of different ages and from specialists as well as general practitioners, speaks for the validity and stability of the observed phenomena. The different forms of early treatment termination are discussed and addressed separately because they each have special risks and are differently associated with treatment failure.

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This study presents a methodological approach to an expost facto investigation of sample bias in drug utilization observation (DUO) studies using the example of a DUO with the nontricyclic antidepressant fluoxetine. A total of 479 psychiatrists and neurologists and 2,401 patients were investigated. The purpose of the study was to judge the representativeness of our DUO sample for two populations: first, for all psychiatrics and neurologists prescribing fluoxetine or all patients being treated with fluoxetine in Germany and, second, for all psychiatrists and neurologists prescribing antidepressants or all patients being treated with antidepressants in Germany. Criteria for the representativeness test were physician variables (gender, size of community where practicing, federal state, age, volume of prescriptions) and patient variables (gender, age, prescription-related diagnosis, concurrent illnesses, concomitant medications). The study shows that the DUO sample can rightfully claim representativeness in the majority of parameters for the psychiatrists and neurologists prescribing fluoxetine and for the patients being treated with fluoxetine. There are more noticeable discrepancies with regard to the psychiatrists and neurologists in general and to the patients being treated with antidepressants in general. The methodological problems of pharmacoepidemiological investigation of representativeness are discussed.