This review discusses the pharmacokinetic and pharmacodynamic parameters that influence the dosing of antibacterials in both animals and humans. Pharmacokinetics refers to the absorption, distribution, and elimination of drugs, while pharmacodynamics relates to the drug's effect on the body. The time course of antimicrobial activity is determined by the interplay between these two factors. Pharmacodynamic parameters such as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) are used to assess the activity of antibacterial drugs. However, they do not provide information on the time course of antimicrobial activity. Parameters like the postantibiotic effect (PAE) and postantibiotic sub-MIC effect (PAE-SME) are important in understanding the duration of antimicrobial activity after drug exposure. The bactericidal activity of antibacterials varies, with some drugs showing concentration-dependent killing and others showing minimal concentration-dependent killing. For example, aminoglycosides and fluoroquinolones exhibit concentration-dependent killing, while β-lactams, vancomycin, clindamycin, and macrolides show minimal concentration-dependent killing. The duration of the postantibiotic effect (PAE) varies among antibacterials. Aminoglycosides and fluoroquinolones have prolonged PAEs, while β-lactams and some other antibiotics have shorter PAEs. The PAE can be influenced by the presence of leukocytes and the simulation of human pharmacokinetics. Pharmacokinetic and pharmacodynamic parameters such as the area under the concentration-time curve (AUC)/MIC ratio and the peak/MIC ratio are important in determining the efficacy of antibacterials. For β-lactams, the time above the MIC is a key parameter, while for aminoglycosides and fluoroquinolones, the AUC/MIC and peak/MIC ratios are important. Studies have shown that the magnitude of these parameters required for efficacy is similar in animal models and humans. However, there is still much to learn, and further research is needed to correlate these parameters with therapeutic efficacy in various infections. The use of pharmacokinetic/pharmacodynamic parameters as guides for establishing optimal dosing regimens for new and old drugs, as well as for new emerging pathogens and resistant organisms, is important for reducing the cost of drug development and improving patient outcomes.This review discusses the pharmacokinetic and pharmacodynamic parameters that influence the dosing of antibacterials in both animals and humans. Pharmacokinetics refers to the absorption, distribution, and elimination of drugs, while pharmacodynamics relates to the drug's effect on the body. The time course of antimicrobial activity is determined by the interplay between these two factors. Pharmacodynamic parameters such as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) are used to assess the activity of antibacterial drugs. However, they do not provide information on the time course of antimicrobial activity. Parameters like the postantibiotic effect (PAE) and postantibiotic sub-MIC effect (PAE-SME) are important in understanding the duration of antimicrobial activity after drug exposure. The bactericidal activity of antibacterials varies, with some drugs showing concentration-dependent killing and others showing minimal concentration-dependent killing. For example, aminoglycosides and fluoroquinolones exhibit concentration-dependent killing, while β-lactams, vancomycin, clindamycin, and macrolides show minimal concentration-dependent killing. The duration of the postantibiotic effect (PAE) varies among antibacterials. Aminoglycosides and fluoroquinolones have prolonged PAEs, while β-lactams and some other antibiotics have shorter PAEs. The PAE can be influenced by the presence of leukocytes and the simulation of human pharmacokinetics. Pharmacokinetic and pharmacodynamic parameters such as the area under the concentration-time curve (AUC)/MIC ratio and the peak/MIC ratio are important in determining the efficacy of antibacterials. For β-lactams, the time above the MIC is a key parameter, while for aminoglycosides and fluoroquinolones, the AUC/MIC and peak/MIC ratios are important. Studies have shown that the magnitude of these parameters required for efficacy is similar in animal models and humans. However, there is still much to learn, and further research is needed to correlate these parameters with therapeutic efficacy in various infections. The use of pharmacokinetic/pharmacodynamic parameters as guides for establishing optimal dosing regimens for new and old drugs, as well as for new emerging pathogens and resistant organisms, is important for reducing the cost of drug development and improving patient outcomes.