Impact of the national centralized volume-based procurement policy on antihypertensive drug procurement, price, and volume in Guangxi: an interrupted time series analysis of procurement data

Introduction: The impact of China's national centralized volume-based procurement (NVBP) policy on antihypertensive drug procurement in underdeveloped, multi-ethnic regions remains understudied. This study evaluated changes in procurement prices, volumes, and costs for four antihypertensive drugs following the second NVBP batch in Guangxi, an economically disadvantaged region in southwestern China. Methods: Monthly procurement data for four NVBP antihypertensive drugs (Olmesartan Medoxomil, Candesartan Cilexetil, Terazosin Hydrochloride, and Indapamide) were collected from January 2019 to April 2021, covering 16 months before and 12 months after policy implementation (May 1, 2020). Interrupted time series (ITS) analysis with Newey-West standard errors was used to assess immediate and sustained changes in log-transformed defined daily doses (DDDs) and defined daily dose costs (DDDc). Sensitivity analyses examined robustness to a January 2021 procurement spike. Results: > 0.05). A sharp DDDs spike occurred in January 2021, followed by a decline. Sensitivity analyses confirmed that the spike did not affect the direction or significance of the main estimates. Discussion: The second NVBP batch was associated with substantial and sustained reductions in procurement prices and costs for these four antihypertensive drugs in Guangxi. However, procurement volumes showed marked volatility without stable long-term growth. These findings, based on procurement records rather than patient-level data, suggest that price reductions alone may not ensure consistent procurement patterns. Strengthening supply chain resilience and aligning procurement schedules with clinical demand may support more stable drug supply in disadvantaged regions.