Degradation Pathway for Eplerenone by Validated Stability Indicating UP-LC Method

Synthesis and Physicochemical Characterization of the Process-Related Impurities of Eplerenone, an Antihypertensive Drug

Two unknown impurities were observed during the process development for multigram-scale synthesis of eplerenone (Inspra^®). The new process-related impurities were identified and fully characterized as the corresponding (7β,11α,17α)-11-hydroxy- and (7α,11β,17α)-9,11-dichloroeplerenone derivatives 12a and 13. Seven other known but poorly described in the literature eplerenone impurities, including four impurities A, B, C and E listed in the European Pharmacopoeia 8.4 were also detected, identified and fully characterized. All these contaminants result from side reactions taking place on the steroid ring C of the starting 11α-hydroxy-7α-(methoxycarbonyl)-3-oxo-17α-pregn-4-ene-21,17-carbolactone (12) and the key intermediate (7α,17α)-9(11)-enester 7, including epimerization of the C-7 asymmetric center, oxidation, dehydration, chlorination and lactonization. The impurities were isolated and/or synthesized and fully characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectrometry/electrospray ionization (HRMS/ESI). Their ¹H- and ¹³C-NMR signals were fully assigned. The molecular structures of the eight impurities, including the new (7β,11α,17α)-11-hydroxy- and (7α,11β,17α)-9,11-dichloroeplerenone related substances 12a and 13, were solved and refined using single-crystal X-ray diffraction (SCXRD). The full identification and characterization of these impurities should be useful for the quality control and the validation of the analytical methods in the manufacture of eplerenone.

Purity Indicating TLC Method for Quantitative Determination of Phenylephrine and Dimethindine Maleate in Presence of Dimethindine Maleate Impurity: 2-ethyl pyridine in Nasal Gel

The aim of this work was to establish, optimize and validate a sensitive, selective and accurate thin layer chromatographic (TLC) method for determination of Phenylephrine (PHE), Dimetindene maleate (DM) and its major toxic impurity; 2-ethyl pyridine (EP), in raw material and nasal gel. The proposed method was applied for analysis of PHE, DM and EP over the concentration range of 1.00–10.0, 0.50–8.00 and 2.00–20.0 µg/band, respectively. The method is based on the separation of three components followed by densitometric measurement of the separated peaks at 254 nm. The separation was carried out on silica gel TLC F254 plates, using toluene: acetone: isopropyl alc.: ammonia (5.3: 2.7: 1.8: 0.4, by volume) as a developing system. The suggested method was validated according to International Conference on Harmonization guidelines and can be applied for routine analysis in quality control laboratories. The results obtained by the proposed method were statistically com-pared with the official method revealing high accuracy and good precision.

The influence of ionizing radiation, temperature, and light on eplerenone in the solid state

Eplerenone was subjected to the influence of ionizing radiation in the form of a high-energy electron beam (25–400 kGy), high temperature (90°C RH 0% and 60°C RH 76.4%), and light (6 mln lux h). An HPLC method was used to determine the content of eplerenone and to establish the impurity profile of all samples. As eplerenone was found to be a compound of great resistance to the above stress factors with the exception of high doses of ionizing radiation (≥200 kGy) when its degradation was above 1%, it is possible to sterilize eplerenone by radiation method with the standard dose of 25 kGy. Based on the analysis of impurities and degradation products, the mechanism of radiodegradation was demonstrated to differ from the mechanisms of photo- and thermodegradation. The observation that the DSC curves for the nondegraded and degraded samples of eplerenone were significantly different only under exposure to the electron beam confirmed the applicability of DSC for studies of radiolytic degradation of eplerenone.