title: Serotonin syndrome probably triggered by a morphine-phenelzine interaction.
abstract: Serotonin syndrome is a potentially life-threatening condition caused by excessive central and peripheral stimulation of serotonin brainstem receptors, usually triggered by inadvertent interactions between agents with serotonergic activity. Evidence supporting an association between nonserotonergic opiates, such as oxycodone or morphine, and serotonin syndrome is very limited and even contradictory. In this case report, we describe a patient who developed serotonergic-adverse effects likely precipitated by an interaction between morphine and phenelzine. A 57-year-old woman presented to the emergency department with complaints of increasing visual hallucinations, restlessness, photophobia, dizziness, neck stiffness, occipital headache, confusion, sweating, tachycardia, and nausea over the previous week. On admission, her blood pressure was 185/65 mm Hg, and clonus was noted in the lower extremities. The patient was hospitalized 10 days earlier for cellulitis of the left breast secondary to a left mastectomy 5 months earlier, and a short course of oral morphine was prescribed for pain control. Her routine medications consisted of aspirin, atorvastatin, bisoprolol, clopidogrel, gabapentin, omeprazole, phenelzine, and ramipril. Supportive measures were initiated on admission. Phenelzine and morphine were discontinued immediately, leading to a progressive resolution of symptoms over the next 48 hours. Phenelzine was restarted on discharge without further complications. Use of the Drug Interaction Probability Scale indicated a probable relationship (score of 6) between the patient's development of serotonin syndrome and the combination of morphine and phenelzine. The mechanism underlying this interaction, however, remains unclear and warrants further investigation. Clinicians should carefully weigh the risk and benefits of initiating morphine in patients taking monoamine oxidase inhibitors or any other serotonin-enhancing drugs.
authors.affiliation: Cancer Services, Pharmacy Department, Northampton General Hospital NHS Trust, Northampton, UK.
authors.forename: Hector
authors.initials: H
authors.lastname: Mateo-Carrasco
authors.affiliation: Oral and Maxillofacial Surgery, Maxillofacial Unit and Orthodontics, Northampton General Hospital NHS Trust, Northampton, UK.
authors.forename: Eva María
authors.initials: EM
authors.lastname: Muñoz-Aguilera
authors.affiliation: Emergency Department, Torrecárdenas Hospital, Almería, Spain.
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: García-Torrecillas
authors.affiliation: UCLH London, London, UK.
authors.forename: Hiba
authors.initials: H
authors.lastname: Abu Al-Robb
mesh_terms: D000701:Analgesics, Opioid / Q000009:adverse effects*; D004347:Drug Interactions; D005260:Female; D006801:Humans; D008875:Middle Aged; D008996:Monoamine Oxidase Inhibitors / Q000009:adverse effects*; D009020:Morphine / Q000009:adverse effects*; D010624:Phenelzine / Q000009:adverse effects*; D020230:Serotonin Syndrome / Q000139:chemically induced*
chemical_list: D000701:Analgesics, Opioid; D008996:Monoamine Oxidase Inhibitors; D009020:Morphine; D010624:Phenelzine
keywords: monoamine oxidase inhibitor; morphine; opioid; phenelzine; serotonin syndrome