Risk of serotonin syndrome in acutely ill patients receiving linezolid and opioids concomitantly: a retrospective cohort study

INTRODUCTION: Linezolid is an oxazolidinone antibiotic with a reversible, non-selective, monoamine oxidase inhibitory effect. Combining linezolid with serotonergic agents may increase serotonin syndrome (SS) risk. Linezolid is recommended in patients with suspected or confirmed resistant Gram-positive bacterial infections, especially if vancomycin cannot be used. However, it is unclear whether co-administration of linezolid with opioids increases the risk of serotonin syndrome. RESEARCH OBJECTIVE: To establish whether combining linezolid with opioids will increase the incidence of SS in acutely ill patients. METHODS: This was a retrospective observational study. All adult patients who were admitted and received linezolid between March and September 2020 were included in the study. The primary outcome was the prevalence of SS, as defined by Hunter's criteria. RESULTS: The study included 106 patients, most whom were males (91.5%). More than half of the cohort (56.6%) received a concomitant opioid agent. Morphine and fentanyl were the most prescribed opioids (37.7% and 34%, respectively). Among patients who received opioids, only one patient (1.6%) had spontaneous clonus. However, this patient developed spontaneous clonus post cardiac arrest, which made an association with the linezolid–opioids combination less likely. CONCLUSION: In this study, the incidence of SS was low in acutely ill patients who received concomitant linezolid and opioids. However, larger prospective studies are required to confirm this finding.