Marked and prolonged serotonin toxicity in a tramadol-poisoned patient with a pharmacokinetic study

Abstract

Background

Tramadol poisoning rarely causes serotonin toxicity, which mechanisms remain poorly understood. We investigated alterations in tramadol pharmacokinetics in a tramadol-poisoned patient who presented with marked and prolonged serotonin toxicity.

Case report

A 21-year-old male self-ingested 750 mg-tramadol, 200 mg-sotalol, 400 mg-propranolol and 6 mg-lorazepam. He was a kidney transplant patient treated with mycophenolate, tacrolimus, prednisone, and paroxetine. He developed transitory cardiovascular failure and prolonged serotonin toxicity requiring sedation, muscle paralysis, and cyproheptadine, with a favorable outcome.

Methods

We measured plasma concentrations of tramadol, M1, M2, and M5 using liquid-chromatography-tandem mass spectrometry, calculated elimination half-lives and metabolic ratios of the compounds, and genotyped cytochromes involved in tramadol metabolism.

Results

Elimination half-lives of tramadol (6.1 h) and M1 (7.1 h) were normal while those of M2 (26.5 h) and M5 (16.7 h) prolonged. M1 metabolic ratio (0.12) was 2-fold reduced, M2 metabolic ratio (197) 1000-fold increased and M5 metabolic ratio (0.12) normal. This metabolic profile in a patient with normal CYP2D6-metabolizer status based on genotyping supports CYP2D6 inhibition by paroxetine and propranolol, two strong mechanism‐based inhibitors. Only M2 present in sufficient concentrations up to 48 h could explain the prolonged serotonin toxicity.

Conclusion

Marked and prolonged serotonin toxicity was attributed to increased M2 production due to paroxetine- and propranolol-related CYP2D6 inhibition of tramadol metabolism.

Keywords:

• Tramadol
• serotonin syndrome
• poisoning
• drug–drug interaction
• pharmacokinetics

Authors’ contributions

B.M. and X.D. designed the study. I.M. and B.M. managed the patient. G.B., L.L. N.K., P.H., and X.D. performed the toxicological analyses. N.P. performed the genotyping. G.B. and X.D. performed the pharmacokinetic study. G.B. drafted the manuscript. B.M. and X.D. revised the initial version. All authors contributed to writing the manuscript and agreed with its final version.

Disclosure statement

The authors report no conflict of interest. The authors alone are responsible for the content and writing of this paper. The manuscript has been read and approved by all authors. The authors certify that the submission is not under review at any other publication. The authors certify that the authors have no other submissions and previous reports that might be regarded as overlapping with the current work. The authors declare no financial disclosures.