Topically used corticosteroids: What is the big picture of drug product degradation?

Corticosteroids are widely used in topical formulations such as creams (aqueous) and ointments (non-aqueous). The generally used corticosteroids show large molecular resemblance, where especially the 20-keto-21-hydroxyl group bound to the 17 carbon is important for their chemical stability. Oxidation in both aqueous and non-aqueous environment occurs for triamcinolone acetonide (TCA), hydrocortisone (HC) and desoximethasone (DS). Besides the 20-keto-21-hydroxyl group, TCA, HC and DS have different other moieties attached to the same C17. These moieties are shown to influence not only the type of degradation product formed but also the degradation kinetics. Seven degradation products are found in total and a degradation mechanism is proposed. Furthermore the transesterfication of betamethasone-17-valerate to betamethasone-21-valerate is shown to occur both in aqueous and non-aqueous environment. Finally, a comprehensive scheme of degradation pathways is presented that is applicable for both aqueous and non-aqueous formulations.

Development and validation of a stability-indicating HPLC-UV method for the determination of triamcinolone acetonide and its degradation products in an ointment formulation.

A stability indicating high performance liquid chromatography method has been developed for the determination of triamcinolone acetonide (TCA) and its main degradation products in ointment formulations. The method, based on extensive stress testing using metal salts, azobisisobutyronitrile, acid, base and peroxide, showed that TCA undergoes oxidative degradation. All degradation products were identified using HPLC mass spectrometry. Separation and quantification was achieved using an Altima C18 RP18 HP column (250×4.6mm2, with 5µm particles) using a mobile phase consisting of acetonitrile and water buffered at pH 7 using 10mM phosphate buffer. A gradient mode was operated at a flow rate of 1.5ml/min and detection was at 241nm. The method showed linearity for TCA and Impurity C in 0.02-125% of the workload, both square roots of the correlation coefficients were larger than 0.9999. Repeatability and intermediate precision were performed by six consecutive injections of both 1.25% and 125% of the work load for both TCA and Impurity C divided equally over two days. RSD were 0.6% and 0.7% for TCA and 0.5% and 0.1% for Impurity C respectively. Accuracy was determined as well, the average recoveries were 99.5% (±0.1%, n=3) for TCA and 96.9% (±1.3%, n=3) for impurity C respectively from spiked ointment samples. The robustness was also evaluated by variations of column (old vs new), mobile phase pH and filter retention. The applicability of the method was evaluated by analysis of a commercial ointment formulation. Interestingly, the extensive stress tests were able to predict all degradation products of TCA in a long term stability ointment sample.