Optimizing critical care pharmacotherapy: dynamic prospective evaluation of the medication regimen complexity-intensive care unit (MRC-ICU) score in critically ill patients.

Medication regimens in critically ill patients are generally complex, increasing the risk of drug-related problems (DRPs) and unfavorable outcomes. This study aimed to evaluate associations between medication complexity and clinical pharmacist (CP) interventions as well as clinical outcomes using the Medication Regimen Complexity-Intensive Care Unit (MRC-ICU) scoring tool. This prospective cohort study was conducted between June 2024 and April 2025 in a medical ICU of a tertiary university hospital. Throughout the study period, medication regimen complexity was assessed daily. CP interventions were systematically documented, and their potential impact was evaluated using the Clinical, Economic and Organizational (CLEO) tool. A total of 202 patients over 2,287 patient-days were evaluated, during which 748 CP interventions were performed. The number of identified DRPs and CP interventions was significantly higher in patients with high MRC-ICU scores (≥ 8) (p < 0.001), among whom interventions with a moderate clinical impact (p < 0.001) and cost-decreasing economic impact (p = 0.002) were also more frequently observed. The MRC-ICU score at 24 h correlated with the number of CP interventions (r = 0.554; p < 0.001). Multivariable regression analysis revealed each one-point increase in the MRC-ICU score at 24 h was associated with a 3.9% increase in the number of CP interventions [incidence rate ratio (IRR): 1.039; p < 0.001]. According to the patient-day analysis, each one-point increase in the daily MRC-ICU score was associated with an 8.4% increase in daily interventions (IRR: 1.084; p < 0.001). Additionally, strong correlations were observed between the MRC-ICU score and the Acute Physiology and Chronic Health Evaluation II (APACHE II) (r = 0.618), the Sequential Organ Failure Assessment (SOFA) (r = 0.720), and the Modified Nutrition Risk in the Critically Ill (mNUTRIC) (r = 0.614) (for all p < 0.001). Furthermore, the MRC-ICU score demonstrated good predictive performance for ICU mortality, with an area under the curve (AUC) of 0.813. The MRC-ICU score stands out not only as a tool to evaluate regimen complexity but also as a valuable and dynamic instrument for predicting the need for CP interventions, supporting patient prioritization, and integrating with clinical risk scoring systems.