Introduction: For the manufacture of small molecule drugs, many pharmaceutical innovator companies have recently invested in continuous processing, which can offer significant technical and economic advantages over traditional batch methodology. This Expert Review will describe the reasons for this interest as well as many considerations and challenges that exist today concerning continuous manufacturing. Areas covered: Continuous processing is defined and many reasons for its adoption are described. The current state of continuous drug substance manufacturing within the pharmaceutical industry is summarized. Current key challenges to implementation of continuous manufacturing are highlighted, and an outlook provided regarding the prospects for continuous within the industry. Expert commentary: Continuous processing at Lilly has been a journey that started with the need for increased safety and capability. Over twelve years the original small, dedicated group has grown to more than 100 Lilly employees in discovery, development, quality, manufacturing, and regulatory designing in continuous drug substance processing. Recently we have focused on linked continuous unit operations for the purpose of all-at-once pharmaceutical manufacturing, but the technical and business drivers that existed in the very beginning for stand-alone continuous unit operations in hybrid processes have persisted, which merits investment in both approaches.

• Eli Lilly & Company

• API
• PAT

1. Active pharmaceutical ingredient
2. API
3. continuous manufacturing
4. continuous processing
5. Drug substance
6. flow chemistry
7. manufacturing
8. pat
9. Review article
10. small molecules