The impact of the national volume-based procurement policy on the use of policy-related drugs in Nanjing: an interrupted time-series analysis

BACKGROUND: In September 2019, the “4 + 7” centralized procurement pilot program was expanded nationwide aiming at reducing drug prices by means of volume-based procurement and using accredited generic drugs for branded drug substitutes. Given the current uncertain effect of the policy outside pilot areas, this study was conducted to evaluate the impact of the National Volume-based Procurement policy on the use of policy-related drugs after expansion. METHOD: A single-group interrupted time series was applied using drug purchase data, covering 25 months from December 2018 to December 2020. Drugs related to the centralized procurement policy were selected as samples, including 25 first-batch policy-related drugs and 56 alternative drugs. Centralized procured drugs can be divided into bid-winning and non-winning products, where non-winning products were sorted into generic and branded drugs, and alternative products were classified according to different degrees of substitution. Purchase volume, expenditures, and daily costs were measured. RESULTS: After the implementation of the policy, a significant increase was associated with the volume of bid-winning drugs (p < 0.001) and the volume of generic and branded drugs decreased immediately. The DDDc of drugs under the same generic name significantly reduced (an instantaneous drop of bid-winning drugs by approximately 25%, 7.62 CNY for generics and 3.07 CNY for branded drugs), saving 48.2 million CNY of drug expenditures. The policy has a significant effect on the drug for the treatment of cardiovascular diseases and exerted little influence on the drug for the treatment of nervous diseases, and the substitution of generics for antitumor-branded drugs was not obvious. In addition, the procurement volume of alternative drugs appeared to be a “carry-over”. CONCLUSIONS: These findings indicated that the policy demonstrated positive effects in terms of price reductions and cost savings and accelerated the substitution of generics against branded drugs. The “patent cliff” for branded drugs has gradually emerged. Besides, a short-term “spillover effect” of the volume of alternative drugs was observed, requiring special attention and vigilance. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12939-023-02006-1.