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 US Food and Drug Administration (FDA) 2020 warning.

Results from a study that included more than 1100 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 in comparison 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, Ontario, Canada, 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 December 19 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 that suggested 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 = 1134, 52.5% men) who were dispensed oral linezolid 600 mg twice daily between October 1, 2014, and January 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%).

Reassuring Findings

Serotonin syndrome occurred in fewer than six patients (< .5%), although the exact numbers were not reported, owing to patient privacy concerns. However, on the basis of fewer than six events, the investigators calculated the risk difference for serotonin syndrome as ranging from −0.5% to 2.3%.

Fewer patients who were taking antidepressants experienced serotonin syndrome compared with those who were not taking antidepressants.

The investigators estimated a propensity score for antidepressant use that incorporated several patient baseline characteristics, including age, sex, rural home address, Charlson Comorbidity Index, estimated glomerular filtration rate, history of substance use disorder, and days of use of linezolid and other serotonergic medications. They then matched patients who were not taking antidepressants with those who were taking antidepressants (n = 166 each).

The adjusted risk difference for serotonin syndrome was lower in the antidepressant group than in the no-antidepressant group (−1.2%; 95% CI, −2.9% to 0.5%).

“Within this 95% CI, the worst-case scenario would be a 0.5% increase in the risk of serotonin syndrome due to antidepressants, which is equivalent to a number needed to harm of 200,” the researchers write.

For secondary outcomes, they found “similar rates” of altered mental status or confusion, hospitalization, and death within 30 days between the two propensity score–matched groups.

The investigators note that their findings have “limitations, due to the nature of retrospective observational studies.” Moreover, these types of studies are “not efficient because they often focus on a particular adverse event.”

Future research should move beyond observational studies to phase 4 studies, which would “prospectively monitor for all types of adverse events,” they write.

Still, “while waiting for higher-quality evidence, our study adds to the existing evidence for the safety of linezolid even in the context of concomitant antidepressants,” the researchers note.

“Based on the existing evidence, clinicians should be reassured that it appears safe to prescribe oral linezolid to patients taking antidepressants, especially if there are limited antibiotic options or alternative antibiotic options would be inferior,” they add.

“Consequential Relevance”

Commenting for Medscape Medical News, Ipsit Vahia, MD, associate chief of geriatric psychiatry and director of digital psychiatry translation at McLean Hospital, Boston, Massachusetts, noted that although studies of drug interactions across age groups “may not accurately reflect the rates of risk for older adults,” the current study focused on linezolid use among older patients.

“One may expect higher rates of serotonin syndrome in older adults, who generally tend to be more sensitive to adverse reactions,” said Vahia, who is also director of the Technology and Aging Lab at McLean and was not involved with the current research.

“However, the study finds the risk to be low with a number needed to harm of 200,” Vahia said.

“This retrospective epidemiologic study does not shed light on why this number may be lower than expected, but it has consequential relevance in clinical practice for the management of severe infections among older adults using antidepressants,” he added.

The study was funded by a Queen’s University Research Initiation Grant. Bai and three of the four other investigators report no relevant financial relationships. Co-investigator Mark Loeb, MD, reports having received personal fees from the Paladin Labs Advisory Committee, the International Centre for Professional Development in Health and Medicine Advisory Committee, and the Sunovion Advisory Committee outside the submitted work. Vahia serves as a consultant for Otsuka, has a research collaboration with Emerald Innovations, and receives honorarium as editor for The American Journal of Geriatric Psychiatry.

JAMA Netw Open. Published online December 19, 2022. Full article

Batya Swift Yasgur, MA, LSW is a freelance writer with a counseling practice in Teaneck, NJ. She is a regular contributor to numerous medical publications, including Medscape and WebMD, and is the author of several consumer-oriented health books as well as Behind the Burqa: Our Lives in Afghanistan and How We Escaped to Freedom(the memoir of two brave Afghan sisters who told her their story).

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