Linezolid-associated serotonin toxicity after escitalopram discontinuation: concomitant drug considerations

Blockade of Serotonin 5-HT6 Receptor Constitutive Activity Alleviates Cognitive Deficits in a Preclinical Model of Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a common inherited disorder caused by mutations of the NF1 gene that encodes the Ras-GTPase activating protein neurofibromin, leading to overactivation of Ras-dependent signaling pathways such as the mTOR pathway. It is often characterized by a broad range of cognitive symptoms that are currently untreated. The serotonin 5-HT₆ receptor is a potentially relevant target in view of its ability to associate with neurofibromin and to engage the mTOR pathway to compromise cognition in several cognitive impairment paradigms. Here, we show that constitutively active 5-HT₆ receptors contribute to increased mTOR activity in the brain of Nf1^+/− mice, a preclinical model recapitulating some behavioral alterations of NF1. Correspondingly, peripheral administration of SB258585, a 5-HT₆ receptor inverse agonist, or rapamycin, abolished deficits in long-term social and associative memories in Nf1^+/− mice, whereas administration of CPPQ, a neutral antagonist, did not produce cognitive improvement. These results show a key influence of mTOR activation by constitutively active 5-HT₆ receptors in NF1 cognitive symptoms. They provide a proof of concept that 5-HT₆ receptor inverse agonists already in clinical development as symptomatic treatments to reduce cognitive decline in dementia and psychoses, might be repurposed as therapies alleviating cognitive deficits in NF1 patients.

Clinical Relevance of Pharmacogenetics in Serotonin Syndrome

Serotonin syndrome is a predictable life-threatening condition that is caused by serotonergic stimulation of the central and peripheral nervous systems. A patient's genetic profile can amplify exposure risk as many serotonergic drugs are metabolized by CYP450 enzymes, and these enzymes may be altered in functionality. We report a case of an elderly man who presented with serotonin syndrome after a dose change in valproic acid 5 weeks prior. His medication list consisted of low-dose serotonergic agents, which is unusual as most cases of serotonin syndrome involve higher doses. A review of his pharmacogenetic profile is presented to retrospectively evaluate the additive risk for serotonin syndrome and implications on resuming serotonergic agents.

Linezolid-induced serotonin syndrome

Linezolid is an oxazolidinone antibiotic, which is a weak, reversible, nonselective monoamine oxidase A and B inhibitor; is known to increase serotonin levels, and has been implicated in the development of serotonin syndrome (SS). There is limited literature on the development of SS with linezolid, when used alone. In this report, we present the case of a 70-year-old female who developed features of SS while being treated with linezolid 600 mg twice daily for pneumonia. The SS in her case was managed with stoppage of linezolid, administration of cyproheptadine, and supportive measures.