PII-080 - IN VITRO COMPARATIVE INHIBITORY PROFILES OF SEVERAL CYP2D6 INHIBITORS AND METABOLIC CAPABILITIES OF CYP2D6*1, CYP2D6*2, CYP2D6*10, AND CYP2D6*17 ON TRAMADOL METABOLISM

N. Nahid¹, S. Kanumuri^2,3, A. Sharma^2,3, D. Wang¹, J. Johnson^1,4; ¹Department of Pharmacotherapy and Translational Research and Center for Pharmacogenomics and Precision Medicine, University of Florida College of Pharmacy, Gainesville, FL, USA, ²Department of Pharmaceutics, University of Florida College of Pharmacy, Gainesville, FL, USA, ³Translational Drug Development Core, University of Florida Clinical and Translational Science Institute, Gainesville, FL, USA, ⁴Division of Cardiovascular Medicine, University of Florida College of Medicine, Gainesville, FL, USA.

Background: Tramadol, prescribed to treat moderate to severe pain, was the 35th most prescribed drug in the US in 2020, and is a prodrug that relies on activation by CYP2D6. 20-30% of pain patients take tramadol concomitantly with FDA-designated strong or moderate CYP2D6 inhibitors, potentially leading to treatment failure. Previous studies showed enzyme-inhibitor affinity varied between different CYP2D6 allelic variants with dextromethorphan and atomoxetine metabolism. However, to our best knowledge, no study compared the metabolism of tramadol in different CYP2D6 alleles in the presence of different CYP2D6 inhibitors. We hypothesize the inhibitory effects of CYP2D6 inhibitors on CYP2D6 mediated tramadol metabolism are inhibitor and CYP2D6 allele-specific.

Methods: Comparative quantitative analyses of four CYP2D6 alleles (CYP2D6*1, CYP2D6*2, CYP2D6*10, and CYP2D6*17) in metabolizing tramadol (substrate) to O-desmethyltramadol (O-dm-tramadol) with or without the presence of CYP2D6 inhibitors (quinidine, paroxetine, and duloxetine) were carried out using recombinant CYP2D6 enzyme Bactosomes. O-dm-tramadol was measured via UPLC-MS/MS. Michaelis constant (Km) and maximum velocity (Vmax) for each CYP2D6 allele and IC50 values for different inhibitors were determined by nonlinear regression analysis using GraphPad Prism software. Intrinsic clearance (CLint) was calculated as Vmax/Km.

Results: Compared to CYP2D6*1, *10 and *17 showed higher Km and lower Vmax, while CYP2D6*2 showed similar Km but higher Vmax. The CLint of tramadol to O-dm-tramadol was almost double for CYP2D6*2 (170%) but was much lower for CYP2D6*10 and *17 (9% and 5%, respectively) compared to CYP2D6*1. The table shows that variant alleles exhibit greater resistance to inhibition (higher IC50) by quinidine in comparison to CYP2D6*1. A similar trend is also evident for duloxetine and paroxetine, though of a lesser magnitude.

Conclusion: Three common CYP2D6 allelic variants showed different metabolic capacities toward tramadol and genotype-dependent enzyme-inhibitor affinity as compared to CYP2D6*1. Further studies are warranted to understand the clinical consequences of drug and CYP2D6 genotype-specific-inhibitor interactions on tramadol activation.