(T1330-08-51) Polarized Light Microscopy: A Versatile Technique in the Reverse Engineering of Entacapone Tablets

Purpose: Having a competitive advantage by being the first to market is a fundamental aspect of the generic pharmaceutical industry, as multiple companies strive to develop generic versions of products going off patent^[1]. Successful launch of a generic product requires comparability to the innovator Reference Listed Drug (RLD). Reverse engineering, also known as deformulation, is a scientific process combining various analytical techniques to decode innovator product’s formulation and process parameters, shortening the timeframe required for generic development^[2]. The Polarized Light Microscope (PLM) is one such analytical instrument for research and identification of bifringent substances, using polarization characteristics of light. It provides comprehensive coverage of key microscopic parameters of innovator formulation. In the present study, reverse engineering was performed on marketed tablets of entacapone (COMTAN^®) using PLM with an aim to understand the grades of excipients used in the RLD. PLM was also useful to identify the granulation process and the stage of addition of super disintegrant. Reverse engineering of Entacapone tablets was thus successfully accomplished.

Methods: COMTAN^® film coated tablets were gently scraped to separate the film coating from the core tablets. Identification of granulation process: The core tablets of RLD were lightly ground to separate granules without breaking and were observed under PLM at 100x magnification. These PLM images were compared with granules separated from placebo tablets produced by direct compression and granulation process. Deciphering diluent grade: Core RLD tablets were placed in a petri dish filled with purified water and were allowed to completely disintegrate. After 24 h, the undissolved particles were observed under PLM at 100x magnification. These PLM images were compared with PLM images of different grades of Micro Crystalline Cellulose (MCC) to identify excipient grade used in RLD. Identifying the stage of super disintegrant addition: To determine whether the super disintegrant was added extra granularly or intra granularly, the granules from the core RLD tablets were observed under PLM directly as well as after being hydrated with few drops of water in a petri plate.

Results: Granulation process: Higher proportion of granules separated from the core RLD tablets were observed to be large and opaque (Figure 1A). The morphology, size and shape of these granules were found to be like granules from placebo tablets manufactured by granulation (Figure 1B) and were different from those granules manufactured by DC process (Figure 1C). Based on the comparison of these PLM images, it appears that the RLD formulation was likely produced using the granulation process. MCC grade: Several insoluble particles were observed after complete disintegration of core RLD tablets in water after 24h. From the product label^[3], these insoluble particles were identified as being composed of API, MCC and Croscarmellose Sodium (CCS). By comparing the PLM images of the disintegrated RLD particles (Figure 2A) with PLM images of various grades of MCC (Figure 2B and 2C), it can be confirmed that the insoluble MCC particles in the RLD formulation are of PH 101 grade, based on their morphology and particle size. Stage of Super disintegrant addition: Figure 1A reveals the presence of free CCS particles, which indicates that CCS has been added extra-granularly in RLD Entacapone tablets. On hydrating the granules from core RLD tablet, disintegration of granules into smaller particles was observed which also showed presence of CCS (Figure 3A) indicating that croscarmellose sodium has been added intra granularly as well. This was compared with hydrated Ac-Di-Sol ^® (CCS) particles for confirmation (Figure 3B). The addition of super disintegrant intra as well as extra granularly could be to aid quicker disintegration of this BCS class IV drug.

Conclusion: The present work demonstrates a simple and universal method to decode RLD’s qualitative formula and manufacturing process using polarized light microscopy as a powerful tool. This can also be combined with several other analytical techniques such as SEM, Raman spectroscopy, powder X-ray diffraction, HPLC and atomic absorption to get more qualitative and quantitative information of the RLD. Cost and speed to market are keys to success for a generic pharmaceutical company and thus, a sound reverse engineering strategy using polarized light microscopy may prove to be effective in reducing development timelines and cost.

References: 1. The Role of Reverse Engineering in the Development of Generic Formulations, Arvind K. Bansal, Vishal Koradia, Pharmaceutical Technology, Aug 02, 2005, Volume 29, Issue 8.
2. Role of Innovator Product Characterization in Generic Product Development, Bhushan Munjal, Vishal Koradia et al., Excipient Applications in Formulation Design and Drug Delivery, Jan 01, 2015, pp 521-538
3. The U.S. Food and Drug Administration. Drugs@FDA: FDA-Approved Drug.

Acknowledgements: The authors would like to thank International Flavors and Fragrances Inc. (IFF) for providing excipient support and to James Du from IFF for technical guidance.