Antioxidative Activity of Remimazolam as a Direct Free Radical Scavenger in Comparison With Midazolam

Introduction Remimazolam, a novel ultra-short-acting benzodiazepine, has seen increasing use in recent years as a general anesthetic for patients with poor cardiac function and older adults due to its hemodynamic stability and rapid recovery profile. Alternatively, it has also become clear through several basic and clinical studies that it suppresses inflammation and oxidative stress. However, its direct free-radical-scavenging activity remains largely unreported. In this study, we aimed to evaluate its direct non-enzymatic scavenging activity against multiple free radical species. Materials and methods A constant amount of eight types of free radicals or singlet oxygen, a reactive oxygen species, was generated in disposable cells. After adding various concentrations of remimazolam to the free radical generation system, the radical scavenging activity of the drug was measured using electron spin resonance spectroscopy with the spin-trapping method. Concentration-response curves for the scavenging activity against free radicals and singlet oxygen were constructed. The 50% inhibitory concentration (IC₅₀) values derived from these curves, and the concentrations of spin traps, were used to estimate the reaction rate constants between remimazolam and free radicals as indicators of the scavenging activity of remimazolam. The IC₅₀ of midazolam against free radicals was also evaluated for comparison. Results Remimazolam scavenged hydroxyl radicals, superoxide anions, ascorbyl free radicals, and singlet oxygen, with reaction rate constants of 4.2×10¹⁰ (standard error=1.5×10¹⁰) M^-1s^-1, 8.6 (5.5) <i>k_G</i> _-CYPMPO, 0.31 (0.13) <i>k</i> _edaravone, and 1.9×10 (3) <i>k</i> _{4-OH_TEMP}, respectively. However, remimazolam did not scavenge nitric oxide, 2,2-diphenyl-1-picrylhydrazyl, or tyrosyl radicals. The reaction rate constant of remimazolam toward the hydroxyl radical was comparable to that of the radical scavenger edaravone (5.2×10¹⁰ M⁻¹s⁻¹). Remimazolam had a higher reaction rate constant against hydroxyl radical than midazolam (1.3×10⁸ M⁻¹s⁻¹). Discussions Remimazolam exhibited a higher radical-scavenging activity than midazolam against multiple free radicals. Notably, remimazolam possesses high scavenging activity, comparable to that of edaravone, particularly against the highly injurious hydroxyl radical. It also demonstrated scavenging activity against the superoxide anion, a reactive oxygen species produced upstream of the chain reactions of free radical generation during ischemia-reperfusion injury. These properties of remimazolam potentially offer beneficial antioxidant effects in anesthetic management.