The current study represents the concurrent analysis of diacerein and meloxicam in their binary mixture by two simple spectrophotometric methods, for the first time without prior separation, namely the dual-wavelength and the zero-crossing derivative spectrophotometry methods. Firstly, the dual wavelength method involves the selection of two wavelengths at the original absorption spectra for each drug in such a way that the subtraction of absorbance readings equals zero for the second drug. Wavelengths at 256.0 and 308.5 nm were chosen for the estimation of diacerein where meloxicam showed equal absorption values. Similarly, wavelengths at 357.0 and 281.0 nm were selected for the determination of meloxicam without any contribution of diacerein. Secondly, the other method depends on derivative spectrophotometry with zero-crossing measurement to solve the spectral overlap problem where diacerein was easily assayed using ²D amplitudes at 265.5 nm with no contribution from meloxicam.
Also, meloxicam was determined by calculating the sum of the absolute values of ¹D amplitudes at 339 and 395 nm, where diacerein was zero-crossing at these wavelengths. The ICH guidelines were used to validate the analytical performance of the adopted methods. For the two adopted methods, diacerein and meloxicam showed perfect linearities in the ranges 2-14 µg/mL and 3-24 µg/mL, respectively, with high correlation coefficients (≥ 0.99975). The validated procedures were effectively used in the concurrent quantification of both drugs either in bulk powders, synthetic mixtures, or laboratory-prepared capsules. Finally, the greenness and whiteness of the adopted methods were assessed and compared among other reported procedures.