Two simple and selective methods were developed for the simultaneous determination of tenofovir fumarate (TEN) and emtricitabine (EMT) in combined tablets. The first method involves the application of first derivative spectrophotometry where the first derivative amplitudes were measured at 298.5 nm for determination of EMT in presence of TEN. The second method involves first derivative of ratio spectra spectrophotometry where the amplitudes at 251.5 nm have been used for quantitation of TEN in the presence of EMT. Different variables affecting each method were carefully investigated and optimized. Reliability and analytical performance of the proposed methods, including linearity, range, precision, accuracy, detection, and quantitation limits, were statistically validated. The methods were successfully applied for the determination of EMT and TEN in laboratory-prepared mixtures and in their combined tablets.

Summary.A simple and selective liquid chromatographic method was developed for the simultaneous determination of tenofovir disoproxil fumarate (TEN) and emtricitabine (EMT) in combined tablets. The method is based on separation of TEN and EMT on a Zorbax SB-C8 column, 5 μm, 4.6 × 250 mm, with a mobile phase consisting of 50 mM disodium hydrogen phosphate-acetonitrile (50:50, v/v). The mobile phase contains 0.1% triethylamine (TEA) and was adjusted to pH 6.0. Quantification of the analytes is achieved with diode array -ultraviolet detector (DAD-UV) at 260 and 280 nm for TEN and EMT, respectively, based on peak area. Different variables affecting the method were carefully investigated and optimized. Reliability and analytical performance of the proposed method, including linearity, range, precision, accuracy, and detection and quantitation limits, were statistically validated. The high-performance liquid chromatography (HPLC) method was successfully applied for determination of each drug in their binary tablets.