Febuxostat is a selective inhibitor of xanthin oxidase, a potent drug used in gout therapy, and is registered in the Republic of Croatia in 2012. Febuxostat still does not have an official monograph in any Pharmacopoeia. In this graduate thesis the development of a capillary electrophoretic method for the analysis of the effect of acid on febuxostat extracted from the Adenuric® tablet was started, within stress studies necessary for the development of the stability-indicating method. Micellar electrokinetic chromatography was chosen as the most suitable method, due to the possibility that with the addition of a surfactant (sodium dodecile sulphate, SDS) both neutral and charged compounds can be differentiated. Several working buffers were tested and the one composed of 20 mM borate buffer pH 9.3 and 50 mM SDS without the addition of organic solvent was shown as the most appropriate one. Ketoprofen was chosen as a suitable internal standard, since the addition of acid did not cause changes in height and area of its peak, unlike pravastatin which, by addition of acid, lactonized and epimerized. The concentration of hydrochloric acid in the amount of 0.1 M was found to be suitable for analysis, while the concentration in the amount of 1 M caused excessive degradation of febuxostat. The exposure time of hydrochloric acid to 0.1 M for 2 hours and 50 minutes resulted in excessive degradation of febuxostat, so it is necessary to determine the appropriate exposure time to the acid as well as the volume and concentration of sodium hydroxide necessary to stop acid hydrolysis. It goes beyond the frameworks of this graduate work and remains a challenge in future research.