ABSTRACT

Introduction: The “Breakpoint MIC Quotient” (BMQ), defined as the ratio of an isolate’s minimum inhibitory concentration (MIC) to the susceptible clinical breakpoint for a given drug–pathogen pair, has been proposed as a simple surrogate of pharmacokinetic/pharmacodynamic (PK/PD) target attainment and therapeutic margin. Although formal definitions are lacking, the BMQ and related indices (e.g., Breakpoint/MIC) are grounded in PK/PD principles and aim to provide a simplified surrogate for estimating the probability of achieving therapeutic success.

Methods: We critically examined available literature describing the concept, rationale, and clinical correlates of the BMQ, focusing on its role in antimicrobial therapy decision-making. Illustrative studies involving Gram-negative and Gram-positive infections were reviewed to explore its relevance and limitations.

Results: Evidence suggests that higher MICs, even within the susceptible range, may narrow the therapeutic margin and increase the risk of treatment failure. Clinical studies, such as those involving cefepime against Pseudomonas aeruginosa and vancomycin against MRSA, show associations between elevated MICs and poorer outcomes, including increased mortality. Quantitative assessments using the BMQ may support antimicrobial optimization through higher dosing or prolonged infusions in severe or high-risk infections. However, limitations include oversimplification of host-pathogen interactions, variability in MIC testing (±1 log₂ dilution), dependence on accurate breakpoints, and reduced applicability in scenarios like biofilm-associated or heteroresistant infections.

Conclusions: The BMQ is a promising conceptual tool for risk stratification and antimicrobial stewardship. While it may inform individualized therapy, its clinical utility requires standardization and validation through well-designed prospective clinical trials before widespread adoption.