In the Pharmaceutical & Nutritional Supplement industries, Shellac is used to provide a protective coating (an excipient) on tablets and capsules, as well as to microencapsulate powders, granules, pellets and edible oils. Shellac coatings can therefore be used for the microencapsulation of nutritional supplements and probiotics. They are a natural sealer, protecting against moisture damage during storage, extending shelf life. Shellac also provides a base for printing trademarks, as well as helping to mask unpleasant tastes and odours.
Shellac was used for many years as an enteric coating because its acidic properties make it resistant to stomach acids, helping to control the rate of drug release (sustained or delayed). This enabled pharmaceutical companies to target the position in the digestive system in which the drug is to be dispersed, including the bowels (small intestine and large intestine or colon), alleviating upset stomachs. Pharmaceutical glaze has traditionally been prepared by dissolving Shellac in an ethanol solution, but its limited shelf-life (typically six to twelve months) means that it is of limited use as an enteric coating today. The limited shelf-life arises due to an esterification (chemical reaction) between the alcohol and the carboxyl groups (acids) contained in Shellac, and polymerisation due to alcohol residues trapped in the coating, which causes the Shellac coating to harden over time. This can cause a delay in the disintegration of the Shellac coating and therefore changes the release profile of the drugs contained within. The polymerisation problems are exacerbated when using Bleached Shellac since the molecular structure is partly changed due to its treatment with sodium hypochlorite. Thankfully, Shellac films prepared using Dewaxed Shellac in aqueous solutions containing ammonia can avoid the esterification and polymerisation problems and have very stable release characteristics, even after extended storage periods.
Pharmaceutical grade Shellac complies with the monographs of the European Pharmacopoeia (Ph.Eur.), the United States Pharmacopoeia (USP) and the Japanese Pharmacopoeia (JP). It is generally recognised as safe in non-parenteral medicines (oral tablets and capsules) licensed in the UK, the Food & Drug Administration’s (FDA) Inactive Ingredients Database (oral capsules and tablets) in the US, and the Canadian List of Acceptable Non-Medicinal Ingredients.
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