Because of the development resistance to antibiotics; enfections, which is treat hardly, become widespread. Unavailable dosage managements (dose, dose interval, route ect.) cause to development of bacterial resistance. Dosage regimen must be considered for rationale antibiotic therapy, which is prevent selection and spread of resistant patogens so therapy can be guarantee. Nowadays; an approach called PK/PD which combines pharmacokinetic and pharmacodynamic properties of antibiotics and so that explain relationship of antibacterial effect with time by dosage, is the most interesting subject for antibiotherapy. Aim of this article to underline basis of PK/PD relation in antibiotherapy and this subject's importance for veterinary medicine.