Lifecycle regulation of narrow therapeutic index drugs: Chinese practices, international benchmarks, and optimization pathways.

Given the narrow therapeutic window, high inter-individual variability, and inherent risks of Narrow Therapeutic Index Drugs (NTIDs), this study systematically analyzes global NTID regulatory policies to explore pathways for optimizing China's lifecycle management system. The ultimate goals are to ensure clinical medication safety and promote the healthy development of the generic drug industry. This research conducts a systematic comparative policy review and narrative synthesis of the current regulatory landscape of NTIDs in China, covering both pre-market and post-market stages. We systematically identified and screened regulatory documents, technical guidelines, and policy statements from major international jurisdictions, including the United States Food and Drug Administration (USFDA), the European Medicines Agency (EMA), Health Canada, and Japan's Pharmaceuticals and Medical Devices Agency (PMDA). The analysis focused on four core pillars: catalog status, bioequivalence (BE) requirements, generic substitution policies, and post-market risk monitoring. China's NTID regulatory system currently under development but has not yet formed a comprehensive, systematic, and dynamically updated framework. Globally, regulatory bodies generally impose stricter lifecycle controls, particularly by narrowing BE acceptance intervals (e.g., AUC to 90.00-111.11%) and requiring replicated study designs (e.g., USFDA). However, significant differences persist in catalog management methods (explicit lists in the US and Japan vs. implicit guidance in the EU), BE limits (e.g., Health Canada's AUC of 90.00-112.00%), and generic substitution policies (e.g., the USFDA's BX rating and state-level substitution restrictions). Deficiencies in China persist in areas such as official catalog establishment and the lack of a scientific, graded substitution system. China should draw on international experience to optimize its NTID regulatory system. Recommended actions include strengthening catalog management and technical standards, improving the regulatory policy framework, establishing a scientific, graded substitution system, prudently advancing volume-based procurement (VPB), and enhancing post-market safety monitoring and risk governance capabilities.