Mechanistic understanding of underperforming enteric coated products: Opportunities to add clinical relevance to the dissolution test

Over the last 70 years several cases of in vivo failure of enteric coated (EC) formulations have been reported. The observed failures seem to be due to the slower than expected in vivo performance of EC products. Upon reaching the intestinal lumen, the dosage form is exposed to a bicarbonate buffered environment at much lower interfacial buffering capacity compared to those applied in compendial phosphate buffers. Hence, there is an urgent need to understand the behavior of EC products in bicarbonate buffer (BCB) and to revaluate the current dissolution methods used for such products. The current pilot study mechanistically investigated the performance of five EC products available in the Canadian market. The evaluated parameters were the buffer system (bicarbonate buffer vs. phosphate buffer), buffer capacity and medium pH. We hypothesized that the performance of EC products in BCB would be different compared with compendial phosphate buffer, giving more physiological insight, and that API properties would impact the dissolution behavior in BCB. The objective of this study was to examine the effect of the aforementioned parameters on the drug release applying physiologically relevant conditions (bicarbonate buffer at low molarities). A first step towards making the use of bicarbonate-based systems more feasible in a quality control setting is also reported. All formulations displayed a fast release in phosphate buffer and complied with the compendial performance specifications. On the other hand, they all had a much slower drug release in bicarbonate buffer and failed the USP acceptance criteria. Also, the nature of the drug (acid vs base) impacted the dissolution behavior in BCB. This pilot study indicates that compendial dissolution test for enteric coated tablets lacks physiological relevance and it needs to be reevaluated. Thus, an in vivo relevant performance method for EC products is needed.