2019 Volume 26 Issue 2 Pages 107-110
Serotonin syndrome is caused by excessive serotonin stimulation at the central and peripheral nerve postsynaptic synapse. Patients present with changes in mental status and symptoms of neuromuscular and autonomic dysfunction. We report 3 cases of serotonergic disorder in patients with chronic pain who received a small dose of duloxetine and tramadol. Patients presented with mental symptoms, sweating, palpitations, and tremor after receiving duloxetine and tramadol. Notably, immediate symptomatic improvement was observed with discontinuation of both medicines or of duloxetine alone. Patients were diagnosed with serotonin syndrome based on careful history-taking. Tramadol metabolism is inhibited by duloxetine (which inhibits CYP2D6). Therefore, it is speculated that the increase in blood concentration of tramadol caused serotonin excess in these patients. Inhibition of tramadol metabolism was attributed to the administration of bicalutamide (CYP3A4 inhibitor) in 1 patient. Clinicians must be aware of drug-drug interactions and closely monitor adverse effects, particularly in patients with chronic pain who receive polypharmacy.
