Fluoxetine Washout Period Before MSLT
Fluoxetine must be discontinued 6 weeks (42 days) before undergoing a Multiple Sleep Latency Test (MSLT). 1
Why Fluoxetine Requires Extended Washout
Fluoxetine has uniquely long pharmacokinetic properties that distinguish it from other antidepressants:
- Fluoxetine's elimination half-life is 1-4 days after single doses, but extends to approximately 4 days after chronic administration 2, 3
- The active metabolite norfluoxetine has an even longer elimination half-life of 7-15 days 2, 3
- This means fluoxetine and its active metabolite can remain in the system for weeks after discontinuation 4
Standard MSLT Medication Discontinuation Protocol
The American Geriatrics Society provides clear guidance on pre-MSLT medication management:
- All REM-suppressing antidepressants (REMS-ADs) should be stopped at least 14 days before MSLT 1
- However, fluoxetine specifically requires 6 weeks of discontinuation due to its prolonged half-life 1
- All stimulants (amphetamines, methylphenidate, modafinil) and sedating medications (benzodiazepines, hypnotics, antihistamines) must also be discontinued at least 14 days before testing 1
Clinical Impact of Inadequate Washout
Patients who discontinue REMS-ADs before MSLT show significantly different results compared to those who remain on these medications: 5
- 12-fold increased odds of having ≥2 sleep-onset REM periods (SOREMs) when antidepressants are properly discontinued 5
- Shorter mean sleep latency (8.77 vs 10.21 minutes) in patients who tapered off REMS-ADs 5
- These differences persist even after controlling for demographic and clinical confounders 5
Critical Pre-Test Requirements
Beyond medication discontinuation, proper MSLT preparation includes:
- Wrist actigraphy for 7-14 days prior to MSLT to objectively document sleep-wake patterns and ensure adequate sleep time 1, 6
- Overnight polysomnography immediately before MSLT with minimum 6 hours total sleep time documented 1, 6
- The PSG must be performed the night immediately before the MSLT, with no discharge between tests 6
Common Pitfall to Avoid
If fluoxetine cannot be discontinued or the 6-week washout is not completed, the MSLT interpretation must include a statement regarding the potential effect of the medication on results, as the test may underestimate true sleepiness and suppress REM onset. 5 This is particularly important because inadequate washout can lead to false-negative results for narcolepsy and other central disorders of hypersomnolence.