Breakpoint Mic

The choice of an antibiotic to be used in case of bacterial infection is one of the most difficult and demanding tasks for a doctor. Knowledge of the characteristics of the antibiotic and the ability to make a correct diagnosis is essential.

The lower MIC (minimum inhibitory concentration) does not always identify the most effective antibiotic, as the relationship between breakpoint (BP) and MIC is more predictive, eg: an antibiotic with MIC = 0.5 and BP = 1 (BP / MIC = 2) is to be considered less effective in vitro than one with MIC = 2 and BP = 32 (ratio = 16).

The effectiveness of an antibiotic therapy is influenced by many factors such as the degree of sensitivity of the microorganism, the pharmacokinetics of the antibiotic (eg ADME absorption, metabolism, distribution, excretion), pharmacodynamics (eg interactions between microorganism and antibiotic) and the factors related to the patient such as his degree of immunocompetence, the site of infection and the presence of prosthetic implants. However, in vitro sensitivity is the most easily measured parameter and clinical studies have demonstrated the clinical importance of sensitivity results expressed in MIC. Therefore the need for an accurate and reliable test can only be confirmed; the therapeutic regimen is one of the few factors that can be modified to improve the patient's prognosis unlike his age, co-morbidities, type of infection. In severe infections, in infections localized in sites where the antibiotic penetrates with difficulty and in immunocompromised patients the result expressed with categories S, I, R has a limited predictive value. In these cases a quantitative sensitivity result is very important since it is clear that there is a difference in the clinical response between an antibiotic with MIC of 0.06 µg / ml and one with MIC of 1 µg / ml when the sensitivity breakpoint for both is "1μg / ml. I dedicate this application to the tenacity of my wife Marina. Knowledge must be transmitted if it can save lives.