The pharmacodynamic and pharmacokinetic (PK/PD) characteristics of antimicrobial agents are the two fundamental pharmacological components which provide a rationale for choosing therapy for intra-abdominal infections, especially when they are serious. It is well known which of the important PK/PD parameters can potentiate therapeutic efficacy. Antimicrobial agents can be subdivided into categories based on whether their activity depends on concentration or exposure time. Therefore, a correct dosing regimen for the time-dependent molecules (i.e. beta-lactams, linezolid, tigecycline) should prolong the maximum exposure time to maintain serum levels over the minimum inhibitory concentration (MIC). The concentration-dependent molecules, on the other hand, which include aminoglycosides and fluoroquinolones, should be administered to reach maximum concentrations, since they are bactericidal in direct proportion to their concentrations and possess a prolonged post-antibiotic effect.