Influence of commonly used excipients on the chemical degradation of enalapril maleate in its solid state: The role of condensed water

The physicochemical stability of enalapril maleate was investigated in the presence of fourteen different excipients divided into four different classes. The extent of a drug-excipient interaction was investigated by following the chemical stability using HPLC. It was found that there is a certain order in the stability of enalapril maleate. Enalapril maleate remained most stable in the presence of: disaccharides > celluloses > starches > superdisintegrants. The amount of degradation can be related to the excipient characteristics. A material with a higher water sorption capacity and lower crystallinity presents a more reactive particle surface. It was revealed that the condensation layer deposited on the surface of the excipient is responsible for the degradation of enalapril maleate. A confirmation was found by changing the surface of the excipient and influencing the environmental humidity that allowed a variable build-up of the condensation layer. For this particle-particle interaction, the microenvironmental pH only presents a minor effect as it was found to not be a determining factor for degradation. Moreover, there appears to be a firm relationship between the degradation of enalapril maleate and the water sorption-activity of excipients.

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About this article: Merel Rachel Bout, Herman Vromans, Influence of commonly used excipients on the chemical degradation of enalapril maleate in its solid state: The role of condensed water, European Journal of Pharmaceutical Sciences, Volume 171, 2022, 106121, ISSN 0928-0987,

Table 1. A: Overview of all used materials for experiments.

Divided class Materials Brand name, supplier, country
Enalapril maleate Enalapril maleate, Zhejiang Huahai Pharmaceutical Co. Ltd., China
Disaccharides Lactose monohydrate Pharmatose 200 M, DFE Pharma, Germany
Spray-dried lactose Supertab® 11SD, DFE Pharma, Germany
Anhydrous lactose Supertab® 21AN, DFE Pharma, Germany
Celluloses Microcrystalline cellulose Vivapur® 101, JRS Pharma, Germany
Silicified microcrystalline cellulose PROSOLV® SMCC 90, JRS Pharma, Germany
Starches Potato starch Native starch – potato based, Roquette, France
Corn starch Meritena® Pharma 141, Tereos, France
Pregelatinized starch C*Gel-Instant® 12,018, Cargill, United States
Partially pregelatinized starch Starch 1500®, Colorcon, United States
Amylopectin Amylopectin from maize, Sigma-Aldrich, The Netherlands
Super-disintegrants Sodium starch glycolate Primojel® type A, DFE Pharma, Germany
Sodium starch glycolate Glycolys® type A, Roquette, France
Croscarmellose sodium Ac-di-sol® SD-711, DuPont, United States
Crospovidone Kollidon® CL, BASF, Germany
Silicon dioxide ZEOFREE® 5162, Evonik Silica, Finland


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