<b>The Effect of Procalcitonin-Guided Use of Antibiotics for Lower Respiratory Tract Infection</b>

Background: Lower respiratory tract infections are a major cause of hospitalization and antibiotic exposure, and procalcitonin-guided strategies have been proposed to reduce unnecessary antibiotic use by improving discrimination between bacterial and non-bacterial respiratory illness. Objective: To compare procalcitonin-guided antibiotic therapy with standard clinician-directed care in terms of antibiotic-use duration and hospital length of stay among patients with lower respiratory tract infection. Methods: This comparative observational study was conducted at the Department of Medicine, Combined Military Hospital, Quetta, A total of 190 patients with clinically or radiologically diagnosed lower respiratory tract infection were included and divided equally into a procalcitonin-guided group and a standard-care group. The primary outcome was duration of antibiotic use, while the secondary outcome was hospital length of stay. Continuous variables were summarized as median with interquartile range and compared using non-parametric methods, while categorical variables were compared using the chi-square test. Results: The median age of participants was 52.50 years, and 75.79% were male. ICU admission was significantly more frequent in the procalcitonin-guided group than in standard care (27.37% vs 10.53%, p=0.003). Median hospital stay was longer in the procalcitonin-guided group (8.00 vs 6.00 days, p<0.001). Although the median antibiotic duration was 7 days in both groups, the antibiotic-use distribution was significantly shifted upward in the procalcitonin-guided group (IQR 6.00-12.00 vs 5.00-9.00 days, p=0.012). Conclusion: Procalcitonin-guided care was associated with longer hospital stay and greater overall treatment burden in this cohort; however, the markedly higher ICU burden in the procalcitonin-guided group suggests that baseline severity imbalance likely influenced these findings.