Different types of antibiotics are used against different type of infections and their killing mechanism may either be concentration dependent or time dependent.
Concentration dependent antibiotics:
Those antibiotics which eradicate pathogenic bacteria by achieving high concentration at the site of binding are termed as concentration dependent antibiotics.
These antibiotics show optimum response in killing bacteria(bactericidal) when their concentration is either equal or greater than 10 times above the MIC (minimum inhibitory concentration) at the site of infection for certain target micro-organism. The pharmacodynamic parameter of such antibiotics can be simplified as a peak/MIC ratio.
Aminoglycosides and flouroquinolones are the classes of antibiotics which show concentration dependent killing of organism.
Time dependent antibiotics:
Those classes of antibiotics whose killing response is dependent on time are termed as time dependent antibiotics. Higher concentration of such drugs does not result in greater killing of organism. “The inhibitory effect can be effective because their concentration exceeds the MIC for the microorganism. Hence, these antibiotics are referred to as time-dependent antibiotics.
For time-dependent drugs, the pharmacodynamic parameter can be simplified to the time that serum concentrations remain above the MIC during the dosing interval (t>MIC)”.They show optimum killing response when the time that the drug remains above the MIC is either equal or greater than 50% of the dosing interval.
Different antibiotics whose response is time dependent are penicillins, cephalosporins, carbapenems, monobactams), clindamycin, macrolides (erythromycin, clarithromycin), oxazolidinones (linezolid).
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