Health-system drivers of outpatient antibiotic use: evidence from prescribing, centralized supply, and catchment populations in public tertiary hospitals in Bihar, India

Background: In low- and middle-income countries (LMICs), antibiotic use is shaped not only by clinical decision-making but also by health-system factors such as centralized drug procurement, supply availability, and population catchment pressures. However, empirical evidence linking outpatient prescribing patterns with state-level antibiotic supply and catchment characteristics remains limited. Bihar, one of India's most populous and resource-constrained states, represents a critical yet under-studied setting for understanding these interactions. Methods: = 8,822). These data were triangulated with state-level antibiotic supply records from the Bihar Medical Services and Infrastructure Corporation Limited (BMSICL) for 2022-2025 and secondary data describing hospital catchment populations. Prescribing indicators, WHO AWaRe classification, essential drug list (EDL) status, and supply-prescription concordance were analysed to assess alignment with antimicrobial stewardship goals. Results: Across all sites, outpatient antibiotic use was characterized by high polypharmacy (4-4.7 drugs per prescription), extensive empirical prescribing, and minimal use of culture-based diagnostics (≤2.6%). Broad-spectrum antibiotics dominated prescribing, with Amoxicillin-Clavulanic acid (42.8%), Azithromycin (13.1%), and Cefixime (6.9%) being most frequently used. While Access-category antibiotic use exceeded 50% at two sites, Watch-category use was disproportionately high at JLNMCH (58%), a hospital serving an extensive rural catchment with long patient travel times. Supply-prescription analysis revealed strong alignment for commonly used antibiotics, indicating stable state-level procurement patterns; however, the continued use of Watch-category and non-EDL antibiotics, including Moxifloxacin, raised stewardship concerns. Notably, irrational fixed-dose combinations were prescribed despite not being supplied, indicating parallel private-sector access. Generic prescribing exceeded 97% across all sites, reflecting a positive institutional norm. Conclusions: Antibiotic prescribing in Bihar's public tertiary hospitals is influenced by the interactions of centralized supply stability, diagnostic constraints, and catchment-level pressures rather than prescriber behaviour alone. Persistent availability of broad-spectrum antibiotics through state procurement may be associated with entrenched prescribing patterns, particularly in high-volume, rural-serving facilities. Effective antimicrobial stewardship in such settings requires context-sensitive strategies that integrate supply-chain reform, strengthened diagnostic pathways, and locally tailored prescriber support, moving beyond uniform, guideline-only approaches.