Dextromethorphan-Bupropion-Esketamine Triadic Pharmacology: Molecular Targets, Enzymatic Interactions, and Risk-Benefit Assessment of a Three-Agent Combination for Treatment-Resistant Depression
- 1Department of Molecular and Developmental Medicine, University of Siena, Viale Bracci 16, 53100 Siena, Italy
- 2European Biomedical Research Institute of Salerno, EBRIS, Via Salvatore De Renzi 50, 84125 Salerno, Italy
- 3Mental Health and Addictions Research Group, Institut d’Investigació Biomèdica de Girona (IDIBGI-CERCA), Departament de Salut, Generalitat de Catalunya, Parc Hospitalari Martí i Julià, Edifici M2, 17190 Salt, Spain
Abstract
Dextromethorphan is extensively O-demethylated by cytochrome P450 2D6 (CYP2D6) to dextrorphan, and the two molecules do not share a target profile. Dextrorphan is the more potent N-methyl-D-aspartate (NMDA) channel blocker; the parent compound is the more potent serotonin transporter inhibitor; their sigma-1 affinities are comparable, so differences in sigma-1 engagement depend on exposure rather than intrinsic affinity. CYP2D6 activity therefore does not scale exposure to a fixed pharmacology; it determines which pharmacology is expressed. This review develops that principle and extends it to a three-agent system. From published unbound concentrations and functional potencies, we calculate a model-derived fractional-target-engagement index. Under the base-case inputs, CYP2D6 inhibition raises the serotonergic index approximately fourfold while reducing the NMDA channel index; deterministic sensitivity analysis shows that the direction is robust to one-at-a-time 0.5-fold to 2-fold perturbations but not to all joint extreme assumptions. Quinidine and bupropion are analyzed as mechanistically distinct proofs of concept, and quinidine-derived exposure estimates are not treated as quantitative surrogates for the dextromethorphan–bupropion steady state. The framework is then applied to the untested question of whether a boosted dextromethorphan combination and esketamine are redundant or complementary. The agents share an NMDA channel mechanism, while CYP2B6 pathway overlap remains a hypothesis-generating observation rather than evidence of clinically relevant competition. No controlled data on the three-agent combination exist, and no therapeutic recommendation is made.
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BibTeX
@article{fagiolini2026dextromethorphanbupropionesketamine,
title = {{Dextromethorphan-Bupropion-Esketamine Triadic Pharmacology: Molecular Targets, Enzymatic Interactions, and Risk-Benefit Assessment of a Three-Agent Combination for Treatment-Resistant Depression}},
author = {Andrea Fagiolini and Alessandro Cuomo and Giulio Corrivetti and Mario Pinzi and Pietro Carmellini and Alessandra Marenna and Francesco Monaco and Annarita Vignapiano and Eva Frigola-Capell and the OPADE Group},
journal = {International Journal of Molecular Sciences},
year = {2026},
month = nov,
doi = {10.3390/ijms272110036},
url = {https://www.mdpi.com/1422-0067/27/21/10036},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Dextromethorphan-Bupropion-Esketamine Triadic Pharmacology: Molecular Targets, Enzymatic Interactions, and Risk-Benefit Assessment of a Three-Agent Combination for Treatment-Resistant Depression
AU - Andrea Fagiolini
AU - Alessandro Cuomo
AU - Giulio Corrivetti
AU - Mario Pinzi
AU - Pietro Carmellini
AU - Alessandra Marenna
AU - Francesco Monaco
AU - Annarita Vignapiano
AU - Eva Frigola-Capell
AU - the OPADE Group
PY - 2026
DA - 2026/11/09
JO - International Journal of Molecular Sciences
DO - 10.3390/ijms272110036
UR - https://www.mdpi.com/1422-0067/27/21/10036
AB - Dextromethorphan is extensively O-demethylated by cytochrome P450 2D6 (CYP2D6) to dextrorphan, and the two molecules do not share a target profile. Dextrorphan is the more potent N-methyl-D-aspartate (NMDA) channel blocker; the parent compound is the more potent serotonin transporter inhibitor; their sigma-1 affinities are comparable, so differences in sigma-1 engagement depend on exposure rather than intrinsic affinity. CYP2D6 activity therefore does not scale exposure to a fixed pharmacology; it determines which pharmacology is expressed. This review develops that principle and extends it to a three-agent system. From published unbound concentrations and functional potencies, we calculate a model-derived fractional-target-engagement index. Under the base-case inputs, CYP2D6 inhibition raises the serotonergic index approximately fourfold while reducing the NMDA channel index; deterministic sensitivity analysis shows that the direction is robust to one-at-a-time 0.5-fold to 2-fold perturbations but not to all joint extreme assumptions. Quinidine and bupropion are analyzed as mechanistically distinct proofs of concept, and quinidine-derived exposure estimates are not treated as quantitative surrogates for the dextromethorphan–bupropion steady state. The framework is then applied to the untested question of whether a boosted dextromethorphan combination and esketamine are redundant or complementary. The agents share an NMDA channel mechanism, while CYP2B6 pathway overlap remains a hypothesis-generating observation rather than evidence of clinically relevant competition. No controlled data on the three-agent combination exist, and no therapeutic recommendation is made.
SN - 1422-0067
ER -