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Serotonin syndrome probably triggered by a morphine-phenelzine interaction
Hector Mateo-Carrasco1, Eva María Muñoz-Aguilera2, Juan Manuel García-Torrecillas3
1Cancer Services, Pharmacy Department, Northampton General Hospital NHS Trust, Northampton, UK.
Pharmacotherapy
|April 24, 2015
Summary
This case report highlights a probable link between morphine and phenelzine (a monoamine oxidase inhibitor) triggering serotonin syndrome. Discontinuing these drugs resolved the patient's symptoms, suggesting a significant drug interaction risk.
Area of Science:
- Neuroscience
- Clinical Pharmacology
- Toxicology
Background:
- Serotonin syndrome is a severe condition from excessive serotonin receptor stimulation, typically due to serotonergic drug interactions.
- Limited evidence exists for non-serotonergic opioids like morphine causing serotonin syndrome.
- This report investigates a potential interaction between morphine and phenelzine.
Observation:
- A 57-year-old woman developed symptoms including hallucinations, confusion, tachycardia, and neck stiffness.
- She was recently prescribed oral morphine for pain while taking phenelzine and other medications.
- Physical examination revealed elevated blood pressure and lower extremity clonus.
Findings:
- The patient's symptoms resolved within 48 hours after discontinuing both morphine and phenelzine.
- The Drug Interaction Probability Scale suggested a probable association (score of 6) between morphine, phenelzine, and serotonin syndrome.
- Restarting phenelzine post-discharge did not cause further complications.
Implications:
- This case suggests a potential risk of serotonin syndrome when morphine is co-administered with monoamine oxidase inhibitors like phenelzine.
- The exact mechanism of this interaction requires further research.
- Clinicians should exercise caution when prescribing morphine to patients on MAOIs or other serotonergic agents.