Stability Indicating Derivative Spectrophotometric Methods for Determination of Valbenazine Tosylate in Bulk and in Formulation

Abstract

Valbenazine tosylate, a benzoquinolizidine derivative, is a highly selective vesicular monoamine transporter 2 (VMAT2) inhibitor. It is the first and the only drug approved by the FDA for the treatment of tardive dyskinesia. Rapid, sensitive, and cost-effective first-order derivative UV spectrophotometric methods have been developed for the estimation of valbenazine in bulk and in its marketed formulation. Preliminary spectrophotometric determination of the drug was carried out in acetonitrile and in 0.1 N HCl with a total of 19 parametric variations for the two methods. The selected three-method variants employing peak–zero (P–0) and peak–peak (P–P) techniques were assessed for their stability, indicating potential in force degraded solutions of the drug. The developed methods were validated with respect to linearity, accuracy, precision, and robustness. Linearity was observed within the concentration range 5.0–70.0 μg/mL with an excellent correlation coefficient (r²) of 0.9998. The limits of assay detection values for the proposed method variants were found to range from 0.89 to 2.75 μg/mL, and quantitation limits ranged from 1.19 to 4.32 μg/mL. The proposed methods were applied for the determination of the drug in its marketed capsule formulation, and percentage recovery was found to range from 94 to 95%.