Population Pharmacokinetics of Esketamine Nasal Spray and its Metabolite Noresketamine in Healthy Subjects and Patients with Treatment-Resistant Depression

Background Esketamine nasal spray is approved for treatment-resistant depression. Objective The objective of this study was to characterize the pharmacokinetics of esketamine and noresketamine in healthy subjects and patients with treatment-resistant depression. Methods Esketamine and noresketamine were measured in > 9000 plasma samples collected from 820 individuals who received esketamine by the intranasal, intravenous, and oral routes. An open linear model for esketamine (three compartments) and noresketamine (two compartments) that included a hepato-portal compartment was developed using NONMEM(R) VII. The effects of covariates on esketamine pharmacokinetics and a model evaluation were performed using conventional methods. Results The fraction of a 28-mg intranasal dose absorbed through the nasal cavity (FRn) is 54% (100% of this fraction is completely absorbed); the remaining 46% is swallowed and undergoes intestinal and first-pass metabolism and 18.6% of the swallowed dose reaches the systemic circulation. The absolute bioavailability of 56 and 84 mg of intranasal esketamine is 54 and 51%, respectively. Esketamine volume at steady state and clearance were 752 L and 114 L/h, respectively. Noresketamine volume at steady state and apparent clearance were 185 L and 38 L/h, respectively. Relative to non-Asian subjects, Asian subjects showed a 64.0 and 19.4% decrease in the esketamine elimination rate constant and noresketamine apparent clearance, respectively. Japanese subjects exhibited a 34% increase in FRn vs other races. Hepatic blood flow decreased by 21.9 L/h for each decade in age in subjects aged > 60 years. These changes resulted in esketamine and noresketamine maximum concentration and area under the concentration-time curve after 24 h post-dose values that were up to 36% higher than those observed in other races or in younger adult subjects. Conclusions Esketamine and noresketamine pharmacokinetics was successfully characterized in healthy subjects and patients with treatment-resistant depression. The model quantified esketamine absolute nasal and oral bioavailability, its hepatic flow-limited clearance and biotransformation to the major metabolite noresketamine, and the influence of intrinsic and extrinsic factors on esketamine pharmacokinetics.