Both the fluoroquinolones and the beta-lactam antibiotics are bactericidal in action. But they work through different mechanism of action. Fluroquinolones are bacterial nucleic acid inhibitor whereas cephalosporins are bacterial cell wall synthesis inhibitor. Their main purpose is to eradicate any bacterial infection by killing the bacteria that is termed as bactericidal action. Being bactericidal their action depends on two different parameters-
I. Action of Cephalosporins depends on how long they remain on plasma above the MIC (Time dependent)
II. Action of Fluoroquinolones depends on what extent of drug in available within the tissue (Concentration dependent)
Why they differ on these two parameters, is there any biochemical factor(s) responsible for their nature of action?
beat lactam antibiotics / cephalosporins act on cell wall of bacteria which is in direct contact with the serum /blood they bind to peptidoglycan in competition to cell forming molecules directly .so as long as it is exposed to antibiotic the action occours .
flouroquinolones act on DNA gyrase enzyme which is inside the cell .So first antibiotic has to be in such concentration that it enters the cytoplasm of bacterial cell to act on DNA through DNA gyrase binding .so serum has to have a definite concentration in tissue for penetration in cytoplasm through cell wall pores .
As cephalosporins act on cell wall of bacteria ,so time is needed to show the good effect .If the fluoroquinolones and the beta-lactam antibiotics are bactericidal in action but the site of action is not same .So cephalosporins action is depended on how much time it remains with contact of the cell where as flouroquinolones on concentration for incresing penetration level for making sound effect ....
Thanks from my heart to Arjyabrata Sarker and Cesira Giordano for up voting my answer ......
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