Length of therapy with selective serotonin reuptake inhibitors and tricyclic antidepressants in Australia

Abstract

Objective: To investigate the proportion of patients starting on either selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) who continued treatment for a period consistent with recommended guidelines for major depression, that is at least 6 months.

Method: Cohort study using a national dispensing claims database involving patients eligible for social security entitlements in Australia. Two 'new user' cohorts were established of patients who were supplied a prescription for either an SSRI (6026) or a TCA (4158) in the first week of April 2000 and who had not received a prescription for any antidepressant in the preceding three months. The main outcome measure was the proportion of patients who were still having any SSRI or TCA prescription, respectively, dispensed between 6 and 8 months after initiation. Additionally, for patients starting on either a leading SSRI (sertraline) or TCA (dothiepin), the proportions of those that remained on these drugs or had changed to other antidepressants were determined. The dispensing data are not linked to reason for prescribing in the national dataset.

Results: 2267 SSRI 'new users' (38%) were still receiving SSRIs 6-8 months later, compared with 1269 (31%) of the 4158 TCA 'new users' (p < 0.001). The difference between the groups occurred early, by the 2-4 month time interval. 1038 (41%) of patients starting on the individual SSRI and 385 (38%) of patients starting on the individual TCA were receiving some type of antidepressant therapy at 6-8 months, with no significant difference (p = 0.6) in the proportions that had changed to another antidepressant.

Conclusions: In 2000, only 40% of patients started on an antidepressant continued to be prescribed some antidepressant therapy 6-8 months later. Patients were more likely to continue on SSRIs as a class than on TCAs and the difference in continuation between these two classes occurred within the first 2 months of therapy. However, patients starting on an individual SSRI or TCA were equally likely to change to another antidepressant.