Tracking Vancomycin MIC Creep: A Five Year Analysis

Abstract

Methicillin resistant Staphylococcus aureus (MRSA) is a known human pathogen capable of causing community and hospital acquired infections worldwide. Treatment options available for MRSA infections are limited, with vancomycin being one of the most common drugs used. It is described in the literature that vancomycin can be ineffective against MRSA isolates with MIC values between 1-2 mg/litre. This slow and steady shift of vancomycin MIC values towards higher side over a period of time is known as “MIC creep”. The present retrospective study was carried out over five year period from January 2019 to June 2023. Staphylococcus aureus isolates from all clinical samples isolated during study period were included in the study. MIC50, MIC90, geometric mean MIC values were determined and analysed using Microsoft Excel. In the present study, the prevalence of MRSA was high (79.6%) in pus and tissue samples followed by blood sample (9.7%). Most of the MRSA isolates (55.80%) in present study exhibited vancomycin MIC of 1 µg/ml, there is no increasing trend of MIC values over a five year period. MIC creep is a slow and steady process which is multifactorial in origin. Regular monitoring of vancomycin MIC trend is advisable as vancomycin is the first-line treatment for culture proven severe infection with MRSA.