CHANNELING OF 3 NEWLY INTRODUCED ANTIDEPRESSANTS TO PATIENTS NOT RESPONDING SATISFACTORILY TO PREVIOUS TREATMENT

The demand for knowledge about differences in effectiveness, tolerabil ity, safety, and economic outcomes between and within groups of antide pressant drugs when used in routine daily clinical practice is growing . For gaining this knowledge, observational pharmacoepidemiologic stud ies are often the most feasible option. However, the results of such s tudies can only be valid if either patient baseline characteristics as sociated with the outcome under study are similar or if differences ca n be adjusted for in the analysis. The aim of this study was to evalua te to what extent and for what type of patients three antidepressant d rugs recently introduced in The Netherlands (mirtazapine, sertraline, and venlafaxine) were prescribed during the first year after their int roduction and whether there were differences compared with longer-avai lable antidepressant drugs. For this purpose, prescription drug histor ies from 20 pharmacies serving a population of approximately 200,000 p ersons were analyzed. One year after their introduction, the newly int roduced antidepressant drugs accounted for approximately 6% of new use s of all antidepressant drugs. In comparison to longer-available antid epressants, the newly introduced antidepressant drugs were more often prescribed for patients with prior prescriptions of another antidepres sant drug (rate ratio [RR] 2.7 [95% confidence interval [CI], 2.3-3.0] ), for patients with prior prescriptions of other psychotropic medicin es (RR 1.3 [95% CI, 1.1-1.4]), and by psychiatrists (RR 1.9 [95% CI, 1 .6-2.2]). In addition, the newly introduced antidepressant drugs seeme d to be more often, although not significantly, prescribed for patient s who had been hospitalized on a psychiatric ward (RR 1.5 [95% CI, 0.9 -2.5]). No differences were observed with regard to age and gender dis tribution, the total number of medicines prescribed, and prescriptions of any cardiovascular or gastrointestinal medicine. These findings su ggest that a significant proportion of the patients receiving one of t he newly introduced antidepressant drugs did not respond satisfactoril y to previous pharmacologic treatment. This channeling phenomenon may have important consequences for the interpretation of observational co mparisons between different antidepressant drugs after their introduct ion.