The stability of prostaglandin E₁ ethylester

The purpose of this study was to identify the conversion pathways of prostaglandin E₁ (PGE₁) ethylester during the stability tests in phosphate buffers (pH 7.4) and saline system at various temperature. A reversed phase HPLC system with a photodiode array detector was used to differentiate the UV spectrum of degradation species. By the comparison of UV spectrum of each chromatographic peak, it was confirmed that the dominate degradation pathway of PGE₁ ethylester in phosphate buffer, as well as in 0.9 % NaCl solution, was the sequential formation of PGA₁ ethylester and then PGB₁ ethylester. A first-order reaction model could be used to describe the degradation of PGE₁ ethylester via this route. The activation energy calculated by Arrhenius equation was 19.83 (2.11) and 21.67 (3.33) kcal/mole, respectively, for the reaction in these two media.