Pharmacokinetic, Protein Binding, and Tissue Distribution Investigations of Viloxazine Enantiomers in Rat Plasma by HPLC–MS/MS Using Polysaccharide-Based Immobilized Chiral Column: A Preclinical Approach to Possible Chiral Switch

Viloxazine has a long past of medical use to treat depression in Europe, and it has lately been repurposed for the treatment of attention-deficit/hyperactivity disorder in the USA in an extended-release formulation. For the first time in this study, viloxazine enantiomers in rat plasma (both male and female) were determined using a sensitive and enantioselective HPLC–MS/MS approach. The enantio-separation was carried out using a Chiralpak IC column with a mobile phase consisting of 10 mM ammonium bicarbonate: methanol (5:95% v/v). The chosen internal standard was lamivudine. The mass detection in multiple reaction monitoring mode (MRM) was used to identify both viloxazine enantiomers and the internal standard with a positive electrospray ionization source. The transitions for viloxazine enantiomers and lamivudine were detected at m/z 238.2 → 100.0 and 229.9 → 112.0, respectively. The lower limit of quantification was 1 ng mL⁻¹, and the technique was verified through a validation varied from 1 to 2000 ng mL⁻¹ in rat plasma and 1–500 ng mg⁻¹ in heart, liver, kidney, and brain tissue for individual viloxazine enantiomers. The intra-day and inter-day precision's relative standard deviations were 5.57% in rat plasma and 5.86% in tissues, while the accuracy's relative errors varied from -12.92% to 11.85%. The validated method was applied to the pharmacokinetic and tissue distribution study of viloxazine enantiomers by following oral administration of 10 mg kg⁻¹ to individual enantiomers and racemic viloxazine to both male and female Sprague Dawley rats. It was established that the pharmacokinetic profile of S-Viloxazine was not statistically different from R-Viloxazine.