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Antimicrobial Principles


Appropriate antimicrobial pharmacotherapy requires knowledge of infecting pathogen, host characteristics and the drug's expected activity against the pathogen.

Pharmacokinetics- describes the relationship of the antimicrobial concentration to time. Pharmacokinetics is associated with absorption, distribution, metabolism, elimination, half-life, volume of distribution and area under the concentration-time (AUC) curve.

Pharmacodynamics- relates the fluctuating drug concentration in blood and at the site of infection administration of dose to the time course of the antimicrobial effects. Pharmacodynamics is associated with peak to MIC ration (peak/MIC), AUC to MIC ratio (AUC/MIC) and the time the drug concentration remains above the MIC (T > MIC).

Bacteriostatic- refers to the property by which the antimicrobial is able to inhibit organism multiplication.

Examples include: macrolides, clindamycin, tetracyclines, sulfonamides and linezolid

Bactericidal- refers to the property by which the antimicrobial is able to kill the organism.

Examples include: beta-lactams, vancomycin, aminoglycosides, fluoroquinolines, daptomycin and metronidazole

Minimum inhibitory concentration (MIC)- defined as the lowest concentration of the antimicrobial that completely inhibits growth of the organism.

Minimum bactericidal concentration (MBC)- defined as the lowest concentration of the antimicrobial that kills the organism.

Time dependent killing- refers to the duration of time that the antimicrobial level exceeds the MIC relative to the dosing interval (T > MIC or AUC/MIC). Antimicrobials that demonstrate time dependent killing typically demonstrate slow bactericidal action and have no or short post antibiotic effect (PAE).

Time Dependent Killing Graph

Examples include: Beta-lactams, vancomycin, macrolides, clindamycin and tetracyclines

Concentration dependent killing- refers to the rate and extent of organism kill are a function of the antimicrobial concentration (peak/MIC or AUC/MIC). Antimicrobials that demonstrate concentration dependent killing typically demonstrate rapid bactericidal action and have prolonged PAEs.

Concentration Dependent Killing Graph

Examples include: aminoglycosides, fluoroquinolones, daptomycin and metronidazole