The lower gastro-intestinal tract plays an important role in optimizing bio-availability and drug absorption – and therefore the effectiveness of many therapies. But delivering sensitive APIs to the right location is a challenge. In a series of ‘real world’ questions, we explore the options and solutions when it comes to the targeted delivery of acid-sensitive APIs.
Question: What applications do enteric capsules have?
Answer: Enteric capsules have many applications. Their principal purpose is to prevent the release of active pharmaceutical ingredients (APIs) in the stomach and to avoid them being exposed to gastric acid. These properties enable dosage forms containing acid-sensitive APIs to transit through the stomach unchanged and fully intact. On transiting the stomach, they are then designed to dissolve when passing through the higher pH (6–7) of the small intestine. The preferred dissolution site can often be tailored to specific levels of pH to target specific site release. These properties enable the enteric delivery of both acid-labile APIs, such as biologics, and those APIs whose bioavailability can be optimized by site-specific release targeting in the distal intestinal tract.
Traditionally, to achieve acid resistance, enteric capsules were manufactured by applying a protective secondary coating to the formulation after filling. This required an additional manufacturing step, usually involving spraying the capsule with a solution or dispersion of polymers in an either aqueous or organic solvent.1 Common polymers used in coating include HPMC-P, polyvinyl acetate phthalate, diethyl phthalate, and cellulose acetate phthalate and methacrylate copolymers.1
To ensure the contents of the capsule are fully protected from acid ingress or leakage of the API, many traditional enteric capsules also require banding or heat sealing. Recent developments in polymer science, pioneered by Lonza, have yielded a unique formulation of existing enteric capsule material that does not require the secondary coating step or heat treatment to achieve full compendial acid resistance. Capsugel® Enprotect® capsules are made using a unique bi-layered polymer technology, comprising an inner shell of HPMC to provide robustness in manufacturing, bonded to an outer layer of HPMC-AS to provide acid resistance for up to 2 hours at pH levels as low as 1.2. The unique properties of this polymer combination provide full compendial protection of the formulation as it transits the stomach. On entering the environment of the intestinal tract, dissolution commences at a pH above 6.0. This creates an intrinsically acid-resistant capsule that not only provides an alternative to enteric coating but can also be customized to achieve targeted site-specific dissolution and payload release profiles.
Learn more about the Capsugel® Enprotect® capsule and how it could help solve your oral-dosage challenge.
Source: 1. Shoaib MH, et al. Polymer coatings for pharmaceutical applications. Published first in April 2020 in: https://onlinelibrary.wiley.com (accessed January 2025).