A 41-year-old man stabilised on phenelzine for refractory depression is to be switched to sertraline after inadequate response. His psychiatrist also plans a later switch from sertraline back to an MAOI in another patient currently on fluoxetine. Which washout intervals are correct?
- A MAOI to SSRI: 24 hours; SSRI to MAOI: 48 hours
- B MAOI to SSRI: 1 week; fluoxetine to MAOI: 2 weeks
- C MAOI to SSRI: 2 weeks; fluoxetine to MAOI: 5 weeks ✓
- D MAOI to SSRI: 4 weeks; fluoxetine to MAOI: 1 week
Correct answer: C. MAOI to SSRI: 2 weeks; fluoxetine to MAOI: 5 weeks
Explanation
When switching from an MAOI to another antidepressant, a washout of at least 14 days is required to clear the MAOI and avoid serotonin syndrome. When switching to an MAOI, most antidepressants need 2 weeks off, but fluoxetine requires 5 weeks because of its long half-life and that of its active metabolite norfluoxetine. This asymmetry is a standard examination point and explains why all shorter-interval options are unsafe.
Reference: Kaplan and Sadock's Synopsis of Psychiatry, 12th ed.
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