Quality by design with design of experiments approach for development of a stability-indicating LC method for enzalutamide and its impurities in soft gel dosage formulation.

A novel ultra-performance liquid chromatographic (UPLC) method has been developed and approved for the quantitative determination of enzalutamide (ENZ) and its impurities in drug product dosage form by applying the quality by design with design of experiments approach. An efficient chromatographic separation was achieved on a Waters ACQUITY CSH C18 (100 × 2.1 mm × 1.7 µm) column in gradient elution mode. A mixture of potassium phosphate monobasic buffer and acetonitrile (10 mm, adjusted to pH 4.0 with 1% orthophosphoric acid) at a flow rate of 0.2 mL min-1 (column temperature at 40°C) under ultraviolet detection at 270 nm was used for quantitation. The peak resolution among ENZ and its impurities (Impurity-1, Impurity-2, Impurity-3, Impurity-4, Impurity-5, Impurity-6 and Impurity-7) was greater than 2.5. Regression analysis confers an R2 value (correlation coefficient) higher than 0.999 for the active substance and impurities. The detection level for ENZ impurities was at a level below 0.015% (0.12 µg/mL). The accuracy levels for different compounds were close to 100%. The inter- and intra-day precisions for ENZ and impurities were evaluated and their relative standard deviation (%) values were less than 3.5. Our results show that the UPLC-UV stability-indicating method will be an essential tool that could determine the drug product's impurities and be useful in regular quality control and stability studies of the ENZ drug product dosage form.