The assessment of the activity of an antibiotic is crucial to the successful outcome of antimicrobial therapy. Non-microbiological factors such as host defense mechanisms, the location of an infection, the underlying disease as well as the intrinsic pharmacokinetic and pharmacodynamic properties of the antibiotic. Fundamentally, antibiotics are classified as either having lethal (bactericidal) action against bacteria or are bacteriostatic, preventing bacterial growth. The bactericidal activity of antibiotics may be growth phase-dependent, and, in most but not all cases, the action of many bactericidal antibiotics requires ongoing cell activity and cell division for the drugs' killing activity.

These classifications are based on laboratory behavior; in practice, both of these are capable of ending a bacterial infection. In vitro characterisation of the action of antibiotics to evaluate activity measure the minimum inhibitory concentration and minimum bactericidal concentration of an antimicrobial and are excellent indicators of antimicrobial potency. However, in clinical practice, these measurements alone are insufficient to predict clinical outcome. By combining the pharmacokinetic profile of an antibiotic with the antimicrobial activity, several pharmacological parameters appear to be significant markers of drug efficacy. The activity of antibiotics may be concentration-dependent and their characteristic antimicrobial activity increases with progressively higher antibiotic concentrations.They may also be time-dependent, where their antimicrobial activity does not increase with increasing antibiotic concentrations; however, it is critical that a minimum inhibitory serum concentration is maintained for a certain length of time. A laboratory evaluation of the killing kinetics of the antibiotic using kill curves is useful to determine the time- or concentration-dependence of .