Washout Period for Fluoxetine Before Starting Linezolid
Wait at least 5 weeks after stopping fluoxetine before starting linezolid to prevent potentially fatal serotonin syndrome. 1
Rationale for the 5-Week Washout Period
The extended washout period is driven by fluoxetine's unique pharmacokinetic profile:
Fluoxetine has an exceptionally long elimination half-life of 4-6 days after chronic administration, and its active metabolite norfluoxetine has an even longer half-life of 4-16 days. 1
After chronic dosing, active drug substance persists in the body for weeks after discontinuation, primarily depending on individual patient characteristics, previous dosing regimen, and length of therapy. 1
The FDA drug label explicitly states that "at least 5 weeks (perhaps longer, especially if fluoxetine has been prescribed chronically and/or at higher doses) should be allowed after stopping Prozac before starting an MAOI." 1
Why This Matters: Serotonin Syndrome Risk
Linezolid is a reversible, nonselective monoamine oxidase inhibitor (MAOI) that can trigger serotonin syndrome when combined with serotonergic drugs like SSRIs. 2, 3
The clinical consequences are severe:
Serotonin syndrome presents with mental status changes (confusion, agitation, anxiety), neuromuscular hyperactivity (tremors, clonus, hyperreflexia, muscle rigidity), and autonomic hyperactivity (hypertension, tachycardia, arrhythmias, diaphoresis). 2
Advanced symptoms include fever, seizures, arrhythmias, and unconsciousness, which can lead to fatalities. 2
Symptoms can arise within 24 to 48 hours after combining medications. 2
Clinical Context and Caveats
While retrospective data suggest that only 2-3% of patients receiving linezolid with SSRIs develop serotonin syndrome 4, the FDA contraindication and drug label guidance must take precedence given the potentially fatal outcome.
Important considerations:
The 5-week washout applies specifically to fluoxetine due to its uniquely long half-life; other SSRIs with shorter half-lives (sertraline, citalopram, paroxetine) require only a 14-day washout before starting an MAOI. 1
If fluoxetine was prescribed chronically or at higher doses, consider waiting even longer than 5 weeks. 1
Linezolid should generally not be administered to patients taking any serotonergic agents because of the potential for serious CNS reactions. 3
If serotonin syndrome develops, treatment requires immediate discontinuation of all serotonergic agents, hospital-based supportive care, and continuous cardiac monitoring. 2