Simultaneous quantification of (E) and (Z) isomers of rilpivirine and four degradation products in bulk and tablets by reversed-phase ultra-high-performance liquid chromatography and confirmation of all by molecular weight.

The (E)-isomer of rilpivirine is an approved antiretroviral drug used to treat human immunodeficiency virus. A simple, fast, accurate, and precise analytical method is required to confirm the quality, purity, efficacy, and safety of drug substances and drug products containing rilpivirine. This research article offers a comprehensive ultra-high performance liquid chromatography method for the simultaneous separation and quantification of (E) and (Z) isomers of rilpivirine, including two amide impurities, one nitrile impurity, and one dimer impurity, in both bulk and tablet forms. After complete validation, the proposed reversed-phase ultra-high-performance liquid chromatography method has proven to be simple, fast, linear, accurate, and precise, with a lower limit of quantification and detection of 0.05 and 0.03 µg/ml, respectively, for all six analytes. Separation was achieved on a Waters Acquity ethylene bridged hybrid Shield RP18 (150 × 2.1 mm, 1.7 µm) column maintained at 35.0°C using a gradient elution of acetonitrile and 0.05% formic acid in 10 mM ammonium formate at a flow rate of 0.30 ml/min. A systematic forced degradation study on the undissolved rilpivirine revealed the formation of acid-base hydrolyzed amide impurities (Impurity-A and Impurity-B), oxidative nitrile impurities (Impurity-C), and Z-isomer and dimer impurities of rilpivirine (Impurity-D and Impurity-E) due to alkaline hydrolysis and photodegradation. The proposed method is primarily appropriate for applications requiring the precise determination of desired and undesired isomers of rilpivirine and its degradation products, such as those involving the safety, efficacy, and quality roles of rilpivirine in bulk and tablet forms. Additionally, the proposed ultra-high-performance liquid chromatography method in combination with a mass spectrometer and photo-diode array detector is helpful for the confirmation and correct identification of all analytes.