Carbapenem-based versus non-carbapenem therapy for hospital-acquired and ventilator-associated pneumonia in a resource-limited setting: a retrospective cohort study of clinical outcomes

Background Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are major causes of in-hospital mortality and antimicrobial resistance (AMR), particularly in low- and middle-income countries (LMICs). Carbapenems are commonly used due to their broad-spectrum activity; however, their efficacy in real-world clinical practices comparing carbapenem with non-carbapenem regimens in these settings is limited. Objectives To compare clinical outcomes between patients receiving carbapenem-based and non-carbapenem therapy for HAP and VAP at a tertiary care hospital in Pakistan. Methods This retrospective cohort study included 93 adult patients (HAP: n = 62, VAP: n = 31) over the period of 1 year. Demographics, comorbidities, microbial isolates, treatment regimen, and clinical outcomes were analyzed using descriptive statistics, chi-square tests, and risk ratio calculations with 95% confidence interval. Multivariable logistic regression was planned to adjust for confounders but was not feasible due to missing severity score and biomarker data. Results HAP was more common in females (63%), while VAP showed a male predominance (52%). The most common pathogens were Acinetobacter spp. (HAP: 11.3%; VAP: 19.4%) and Pseudomonas aeruginosa (HAP: 11.3%; VAP: 16.1%). The most prevalent comorbidity in HAP was diabetes mellitus (38.7%). Carbapenem-based therapy (meropenem) was used in 65.6% of cases and the most frequently prescribed non-carbapenem agents were piperacillin-tazobactam, ceftazidime, and colistin. No significant difference in mortality was observed between carbapenem and non-carbapenem therapy in HAP (31.6% vs. 29.2%; RR 1.08, 95% CI 0.50–2.36, p = 0.840) or VAP (65.2% vs. 50.0%; RR 1.30, 95% CI 0.61–2.77, p = 0.440). VAP was associated with significantly higher crude mortality than HAP (61.3% vs. 30.6%; p = 0.005). Crude mortality rates appeared highest among patients in the Acinetobacter baumannii group (70.4%) and Pseudomonas aeruginosa group (31.3%), though treatment group difference were not statistically significant. Conclusion In this single-center retrospective cohort, no statistically significant association between carbapenem-based therapy and all-cause in-hospital mortality was detected in HAP or VAP. Crude mortality appeared highest among patients with Acinetobacter and Pseudomonas isolates. However, wide confidence intervals, treatment-selection bias, and unadjusted analyses preclude definitive conclusions. These findings should be considered hypothesis-generating, requiring confirmation in adequately powered, larger prospective studies.