Background: The long elimination half-lives of fluoxetine and norfluoxetine, the active metabolite of fluoxetine, are of potential consequence when alternative antidepressant agents are introduced after the termination of fluoxetine therapy. It is not known whether paroxetine, an antidepressant agent in the same pharmacologic class as fluoxetine, can be substituted for fluoxetine without the need for an intervening washout period. The objective of this trial was to assess the tolerability of an immediate switch from fluoxetine to paroxetine therapy.
Method: Patients who were treated for moderate to moderately severe major depressive disorder (DSM-III-R 296.2 or 296.3) with a stable dose of fluoxetine for a minimum of 6 weeks' duration were randomized in a double-blind fashion to one of two treatment groups. One group (N = 123) was started on 20 mg of paroxetine daily the morning after their last dose of fluoxetine, and the other group (N = 119) was started on 20 mg of paroxetine daily following a 2-week placebo-washout period. Patient visits were scheduled at weekly intervals for a total of 4 weeks. Adverse experience monitoring was conducted at each visit.
Results: There was no difference in the proportion of patients who discontinued prematurely from the trial due to an adverse experience. Eight patients in the immediate-switch group and 6 patients in the placebo-washout group withdrew from the trial in response to an adverse experience (p = .63, chi-square). The overall profile of adverse experiences was similar in the two treatment groups over the 4-week period. The incidence of adverse experiences in the first 2 weeks following the initiation of paroxetine was generally lower in the group with the intervening 2-week placebo-washout period.
Conclusion: The immediate switch from fluoxetine to paroxetine was as well tolerated as the switch to paroxetine after a 2-week placebo-washout period.