Minimum Inhibitory Concentration (MIC) is the lowest concentration of an antibiotic that inhibits visible growth of a microbial isolate. In critically ill patients there is great variability of antibiotic concentrations in serum due to organ failure which greatly affects pharmacokinetics. MICs should be considered for life threatening infections (i.e. endocarditis, meningitis, osteomyelitis, sepsis, pneumonia), infection sites with poor diffusion of antibiotics or protected from host defences (i.e. CNS, eye, osteomyelitis, endocarditis, cystic fibrosis), immunocompromised patients (i.e. transplant, neonates, hematology, oncology, rheumatology) and critically ill, high risk or unstable patients (i.e. ICU, renal, burns). MICs helps to select antibiotics with a lower MIC relative to the achievable levels and the S breakpoint, adapt antibiotic dose and/or dosing interval for better efficacy and fewer side effects and when considering combination of antibiotics. MIC with Therapeutic Drug Monitoring are becoming essential for treatment customization, improve patient outcome, reduce antibiotic side effects, limit resistance and protect existing antibiotics and may help contain healthcare costs. Automated MIC detection methods benefits the clinician, pharmacist, and infection control team by providing AST results faster (with autoposting to the LIS), assisting with infection control by helping detect resistance and making therapeutic corrections to AST results based on phenotype detected, eg. forcing beta-lactam antibiotics (except ceftaroline and ceftobiprole) resistant when organism is MRSA. The conventional broth dilution method is cumbersome and time consuming and laboratories must use automated AST system for early initiation of the accurate antibiotic therapy in the patients.