i don't mean to sound like a broken record, but you can always find out this information on the prescribing information that the FDA requires all medications to have.
simply go to www.zyvox.com.
when i went there, this is what I found:
"Unless patients are carefully observed for signs and/or symptoms of serotonin syndrome,
linezolid should not be administered to patients with carcinoid syndrome and/or patients
taking any of the following medications: serotonin re-uptake inhibitors [lexapro is an ssri], tricyclic antidepressants, serotonin 5-HT1 receptor agonists (triptans), meperidine or buspirone"
"Spontaneous reports of serotonin syndrome associated with the co-administration of
ZYVOX and serotonergic agents, including antidepressants such as selective serotonin
reuptake inhibitors (SSRIs), have been reported.
"Where administration of ZYVOX and concomitant serotonergic agents is clinically
appropriate, patients should be closely observed for signs and symptoms of serotonin
syndrome such as cognitive dysfunction, hyperpyrexia, hyperreflexia and
incoordination. If signs or symptoms occur physicians should consider discontinuation
of either one or both agents. If the concomitant serotonergic agent is withdrawn,
discontinuation symptoms can be observed (see package insert of the specified agent(s)
for a description of the associated discontinuation symptoms)."
"Serotonergic Agents: Co-administration of linezolid and serotonergic agents was not
associated with serotonin syndrome in Phase 1, 2 or 3 studies. Spontaneous reports of
serotonin syndrome associated with co-administration of ZYVOX and serotonergic agents,
including antidepressants such as selective serotonin reuptake inhibitors (SSRIs), have been
reported. Patients who are treated with ZYVOX and concomitant serotonergic agents
should be closely observed as described in the PRECAUTIONS, General Section. "
If I were you, I would just make sure you were closely monitored. I know being on Lexapro has helped you a lot (and SSRI's help many CFer's.... our bodies are under such stress dealing with CF it's not uncommon for us to not have enough serotonin) so hopefully your doc will be open to letting you take both at the same time and just monitor for serotonin syndrome.
take care