From the Journals

Is the FDA serotonin syndrome warning unnecessary?



The oral antibiotic linezolid does not increase risk for serotonin syndrome in patients taking antidepressants, new research suggests – contradicting a U.S. Food and Drug Administration 2020 warning.

Results from a study that included more than 1,100 patients who were prescribed linezolid, about 20% of whom were also taking antidepressants, showed that serotonin syndrome occurred in fewer than 0.5% of participants – and that the percentage was actually lower among those who took antidepressants, compared with those who did not.

A comparison of participants who took antidepressants to propensity-matched patients who did not take antidepressants showed similar rates of altered mental status, hospitalization, and death between the two groups.

“In this cohort study of older patients who were prescribed linezolid, serotonin syndrome occurred rarely [and] concurrent antidepressants did not significantly increase the risk of serotonin syndrome,” Anthony Bai, MD, division of infectious diseases, department of medicine, Queen’s University, Kingston, Ont., and colleagues write.

“These findings suggested that linezolid is likely safe for patients receiving antidepressants. Nevertheless, prescribers should remain vigilant for this potential drug interaction,” they warn.

The findings were published online in JAMA Network Open.

Scarce data

Linezolid, a synthetic oxazolidinone antibiotic active against resistant gram-positive bacteria, has bioavailability of 100%, “making it ideal as first-line or step-down oral antibiotic therapy for bacteremia and pneumonia as well as skin and soft tissue infections,” the researchers write.

However, they note its use has been “limited because of concerns of drug interactions,” since it can reversibly inhibit monoamine oxidase (MAO).

Thus, “coadministration with antidepressants, such as nonselective MAO inhibitors, selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and bupropion, may precipitate serotonin syndrome,” they write.

The investigators note that many patients who were taking antidepressants and who also needed linezolid for an infection “could not receive it because of this relative contraindication.” They add that data on the risk of serotonin syndrome associated with linezolid are “scarce” and are based largely on case reports or case series from passive surveillance.

Although a previous review of linezolid trials found “no conclusive evidence” that it increased risk for serotonin syndrome in patients taking serotonergic medication, data on patients outside of trials “are lacking.” In addition, an observational study suggested that an increased risk had a small sample size that “likely led to imprecise estimates with a wide CI and inconclusive results,” the researchers write.

Therefore, they sought to fill the knowledge gap by retrospectively analyzing data drawn from the ICES database, an independent nonprofit research institute funded by the Ontario Ministry of Health. This was done in order to “estimate the incidence of serotonin syndrome and how this risk changes because of concomitant antidepressant use in patients receiving linezolid treatment,” they write.

The study included a convenience sample of Ontario-based adults (n = 1,134, 52.5% men) who were dispensed oral linezolid 600 mg twice daily between Oct. 1, 2014, and Jan. 1, 2021. All patients were followed for 30 days.

Of these participants, 19% were also taking antidepressants. Close to half (47.9%) were taking an SSRI, 16.7% were taking an SNRI, 7% were taking a tricyclic antidepressant, and 3.3% were taking a norepinephrine and dopamine reuptake inhibitor.

Patients were divided into groups on the basis of age: 66-69 years (19.8%), 70-79 years (41.7%), and 80 years or older (38.4%).


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