Capsules made from gelatin predominate; however, recent years have seen an increased interest and availability of nongelatin capsules. Such alternative shell compositions may satisfy religious, cultural, or vegetarian needs to avoid animal sources. Hard-shell capsules made from starch were developed by Capsugel, a Division of Pfizer, Inc. (Peapack, New Jersey, U.S.). These consist of two parts—fitted cap and body pieces that are made by injection molding the glassy mass formed when starch containing 13% to 14% water is heated, and then dried (4). Temperatures in the range of 140°C to 190°C reportedly produce masses that flow satisfactorily without degradation. The two parts are formed in separate molds. Unlike hard-gelatin capsules that are supplied with the caps and bodies prejoined, the two parts are supplied separately. The caps and bodies do not interlock and must be sealed together at the time of filling to prevent their separation. Capsugel has licensed this technology to West Pharmaceutical Services, Lionville, Pennsylvania, which uses the starch capsule in their TARGIT® technology for site-specific delivery to the colon. TARGIT is based on the application of enteric polymer coatings to the starch capsules (5).
Hard shells manufactured from hypromellose, the United States Pharmacopeia-National Formulary (USP-NF) official title for hydroxypropylmethylcellulose (HPMC), are also available, for example, Quali-V® (Qualicaps Inc., Whitsett, North Carolina, U.S.) and Vcaps® from Capsugel. Like hard-gelatin capsules, hard-shell HPMC capsules can be formed using a dipping technology. In the case of gelatin capsules, the shells are formed by the gelation (on cooling) of an aqueous gelatin composition that clings to the surface of mold pins (described in more detail later in this chapter). To use the dipping technology, certain additives must be added to HPMC to promote the formation of a gelling system. In one example, small quantities of carrageenan (lowers the thermal gelation temperature) and potassium chloride (promotes gelation) are added (6). In another example, the gelling system consists of gellan gum and potassium acetate (7). Both gellan gum and carrageenan are negatively charged polysaccharides; hence, the positively charged potassium cations promote gelation by reducing the electrostatic repulsion of the polysaccharide chains (7).
Nongelatin soft-shell capsules have also been introduced in recent years. For example, Catalent Pharma Solutions (Somerset, New Jersey, U.S.) has developed Vegicaps® Soft Capsules, the shells of which consist of modified starch, carrageenan, disodium phosphate, glycerin, and/or sorbitol (8). Another starch-based soft-shell capsule, VegaGels®, is available from Swiss Caps USA, Inc. (Miami, Florida, U.S.) (9). Both sources form and fill capsules in a rotary die process similar to that used to produce soft-gelatin capsules.
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