Abstract
Background/Objectives: Antimicrobial resistance poses a severe global threat, particularly in low- and middle-income countries. Hospitalized patients in internal medicine wards are vulnerable to inappropriate antibiotic exposure. This study aimed to evaluate antibiotic utilization patterns, standardize volumetric consumption, and assess the appropriateness of antibiotic prescribing against national guidelines in the Internal Medicine service of a secondary-care hospital in Mexico. Methods: A retrospective descriptive drug-utilization study based on hospital records was conducted from July 2023 to December 2024. During this period, 1127 admissions to the Internal Medicine service were recorded; 413 eligible patients who received at least one systemic antimicrobial agent were included, accounting for 769 prescription events. Antimicrobial consumption was expressed as Defined Daily Doses (DDDs) per 100 admissions according to WHO ATC/DDD methodology. A focused prescribing-appropriateness assessment was performed for the five most frequently prescribed antimicrobial agents (n = 439 prescription events). Results: The cohort had a mean age of 61.4 ± 18.2 years, and 51.3% were aged ≥65 years. Cephalosporins (30.4%) and carbapenems (16.1%) were the most frequently prescribed pharmacological classes. Ceftriaxone had the highest standardized utilization density (49.69 DDDs/100 admissions) and an 80.6% prescribing-alignment rate. Meropenem followed with 44.72 DDDs/100 admissions despite substantially fewer prescription events. The largest proportions of prescription events classified as opportunities for optimization were observed for levofloxacin (48.5%), vancomycin (41.4%), and meropenem (36.1%). Conclusions: High overall guideline alignment (73%) coexisted with substantial use of broad-spectrum antimicrobials. Stewardship prioritization should integrate quantitative utilization with qualitative prescribing assessment rather than interpret total DDD burden as avoidable exposure. These findings provide a baseline for targeted antimicrobial stewardship and clinical-pharmacy interventions in a resource-constrained secondary-care setting.