Spectrofluorimetric Methods for Estimation of Valbenazine Tosylate in Bulk and in Capsule Formulation

Valbenazine tosylate, a benzoquinolizidine derivative, is a highly selective vesicular monoamine transporter 2 inhibitor. The drug has been approved by the FDA as the first and only approved treatment for tardive dyskinesia. To our knowledge, this is the first report on the development and validation of simple, rapid, sensitive, and cost-effective spectrofluorimetric methods based on the native fluorescence of the drug in acidic, basic, and neutral media. The stability-indicating potential of the method was assessed by recovery studies in the forced degraded solutions of the drug. The method was validated in accordance with the International Council for Harmonisation guidelines with respect to linearity, accuracy, precision, limit of detection, limit of quantification, and robustness. Excellent linearity was noted within the concentration range 2.0–30.0 μg/mL (0.1 N hydrochloric acid), 0.5–15.0 μg/mL (0.1 N sodium hydroxide), 0.1–20.0 μg/mL (water) with corresponding correlation coefficients of 0.9963, 0.9989, and 0.9998. Limits of detection and quantitation for the proposed methods were found to range from 0.025 to 0.044 and from 0.077 to 0.1357 μg/mL, respectively, for the three methods. The proposed methods were used to quantify the drug in its marketed capsule formulation, with good recoveries suggesting their applicability to routine analysis of the drug in bulk as well as in formulation.