Lower Extremity Infection

One of the trickiest issues in prescribing linezolid for patients with MRSA or VRE infections is the potential for a drug-drug interaction, leading to serotonin syndrome (SS), with various serotonergic psychiatric medications.  It seems that every pharmacy computer system in the world goes crazy with warnings when you attempt to write for this antibiotic while the patient is on these meds.  The package insert for linezolid states that it is contraindicated to use linezolid in combination with SSRIs, tricyclic antidepressents, triptans, meperidine or buspirone “Unless patients are carefully observed for signs/or symptoms of serotonin syndrome…” On October 20 the FDA updated information on this potential interaction. ( http://www.fda.gov/Drugs/DrugSafety/ucm276251.htm ).  They are now saying that not all serotonergic psychiatric drugs have an equal capacity to cause SS.  Most patients reported to the FDA with SS were taking SSRIs or serotonin norepinephrine reuptake inhibitors (SNRI).  They report that it is currently unknown whether co-administration of linezolid in patients taking other psychiatric drugs carries a comparable risk.  SSRIs and SNRIs that have been implicated include the following drugs commonly seen in lower extremity practice; paroxetine (Paxil, Paxil CR), fluoxetine (Prozac), citalopram (Celexa), escitalopram (Lexapro), venlafaxine (Effexor) and duloxetine (Cymbalta).  The FDA lists the risk as “unclear” in tricyclic antidepressants, MAO inhibitors and a number of other psychiatric drugs.   The reader is directed to the above link for the full list.  What does all of this mean to the practicing provider?  A review of the literature reveals a number of isolated case reports of SS in patients receiving linezolid.  There are few large patient series reported.  In 2006 Taylor et al from the Mayo Clinic reported on a retrospective review of 52 patients who received concomitant linezolid and SSRI therapy while 20 received therapy within 14 days of each other but not concomitantly ( http://www.ncbi.nlm.nih.gov/pubmed/16779744 ).  They found only 2 patients (3%) had a “high probability of SS”