Application of DASC and AUSC metrics in evaluating antimicrobial stewardship interventions in critically ill patients

Objective Conventional metrics reflect use volume, not spectrum breadth, limiting de-escalation assessment. Using days of antibiotic spectrum coverage (DASC) and antibiotic spectrum coverage use (AUSC), we applied a dual-dimensional framework stratified by restriction level to evaluate the impact of antimicrobial stewardship interventions on consumption and spectrum coverage in critically ill patients with infections. Methods In this single-centre retrospective before–after intensive care unit study, an antimicrobial stewardship program optimized prescribing and reduced broad-spectrum exposure. Antimicrobial use was stratified by restriction level and evaluated using conventional metrics, spectrum-based metrics and derived ratio metrics. Results A total of 200 patients were included, and baseline characteristics were comparable between the two groups. Among 200 patients (100 per period), median DDDs decreased from 26.25 to 17.90 (r = 0.223, 95% CI 0.087–0.351; P = 0.002), DOT from 24.00 to 14.00 days (r = 0.294, 95% CI 0.162–0.420; P < 0.001), and DASC from 219.50 to 135.00 (r = 0.290, 95% CI 0.156–0.413; P < 0.001). No statistically significant between-period differences were detected for AUD, AUSC, DASC/DOT, or AUSC/AUD. In the non-special-use stratum, DASC (114.50–63.50; r = 0.242, 95% CI 0.106–0.368; P < 0.001), AUD (99.87–87.24; r = 0.157, 95% CI 0.018–0.289; P = 0.027), and AUSC (923.93–761.25; r = 0.151, 95% CI 0.012–0.284; P = 0.033) were lower in the intervention period; no statistically significant differences were detected in the special-use stratum. AUD correlated with AUSC (Spearman ρ = 0.75), as did AUSC with DASC (ρ = 0.40; both P < 0.01). Length of stay was also shorter (median 15.00 vs. 11.00 days; P < 0.001) and cumulative use correlated with it (ρ = 0.74–0.79); after accounting for observation time, only the treatment-day rate remained significantly lower (adjusted IRR 0.834, 95% CI 0.736–0.944, P = 0.004). Conclusion In this before-after study, cumulative DDDs, DOT, and DASC were lower during the intervention period, partly reflecting shorter length of stay. After adjustment, only the antibiotic treatment-day rate remained significantly lower, whereas DASC/DOT and AUSC/AUD were unchanged. DASC and AUSC may complement conventional metrics for describing spectrum exposure, but require further validation against prescribing appropriateness and clinical outcomes.