The lower gastrointestinal tract is critical for enhancing bioavailability and drug absorption, directly influencing therapeutic efficacy. However, ensuring that sensitive active pharmaceutical ingredients (APIs) reach their intended site remains a challenge. Through a series of practical questions, we examine strategies and technologies for the targeted delivery of acid-sensitive APIs.
Question: How does enteric coating work?
Answer: Enteric coating is used to facilitate the delivery of a drug formulation to the small intestine without it being adversely affected by the acidic environment of the stomach, specifically by premature dissolution of the capsule. Although the enteric coating provides protection from acid, it has the disadvantage of requiring a secondary step in the manufacturing process, after the capsule has been filled and closed. The coating step usually involves spraying a solution or dispersion of polymers in an either aqueous or organic solvent.1 Common polymers used in coating include hydroxypropyl methylcellulose phthalate (HPMC-P), polyvinyl acetate phthalate, diethyl phthalate, cellulose acetate phthalate and methacrylate polymers.1,2 These polymers provide acid resistance, with dissolution subsequently occurring at the higher pH levels encountered in the small intestine, which typically range between 6.0 and 7.4. Additionally, many coated capsules then require the application of heat to dry or seal them to prevent the ingress of acid or premature leakage of the active pharmaceutical ingredients (APIs).
Until recently, enteric coating was the only viable way of achieving protection from the acidic environment of the stomach; however, a new and unique polymer capsule technology developed by Lonza obviates the need for secondary coating, heating or sealing. Capsugel® Enprotect® capsules are made using a unique bi-layered combination of polymers, comprising: (1) an inner shell of hypromellose (HPMC) to provide robustness in manufacturing, bonded to (2) an outer layer of hypromellose acetate succinate (HPMC-AS) that provides compendial compliant acid resistance and dissolution in environments with a pH above 6.0. This creates an intrinsically acid-resistant capsule that not only provides an alternative to enteric coatings 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.
Sources:
1. Shoaib MH, et al. Polymer coatings for pharmaceutical applications. Published first in April 2020 in: https://onlinelibrary.wiley.com. (accessed January 2025.)
2. Sabatini V, et al. Polymers (Basel). 2021;13(5):809. doi: 10.3390.