The sensitivity of bacteria to antibiotics in microbiological study is determined by the MIC ( minimal inhibitory concentration) expressed in mg/L and is the amount of antibiotics that in vitro cause inhibition of growth in 90 % of the pathogen.
As a rule, for the optimal theraupeutic effect, the concentration of antibiotic in the blood must exceed the MIC 3-4 times. However, in patients with immunodeficiency(1) and in hard-to-reach foci of infection (abscesses, meningitis) (2) antibiotics should be used in doses that are much higher than the MIC. The dose-dependent antibiotics of choice include aminoglycosides, fluoroquinolones.
(1) Immunodeficiency - There is a risk that the therapeutic dose of the antibiotic will not lead to the destruction of all bacteria. The immune system is unable to coordinate the destruction of residual bacteria and completely eliminate them from the macro-organismas it is depressed. Several or even one microorganism that have prodused resistance to antibiotics and not killed by immune system cause a relapse of the disease that can not be treated to a previously used antibiotic.
(2)abscesses, meningitis - hard-to-reach foci require higher dosases of antibiotics to cross biological barriers of abscess wall or the blood-brain barrier and reach the cells of the pathogen.