This study evaluated the theoretical clinical outcome of three marbofloxacin posology regimens in two groups of pigs (weaners and fatteners) for the treatment of Actinobacillus pleuropneumoniae (App) and Haemophilus parasuis (Hp) infection and the appearance of resistant bacteria due to the antibiotic treatment. The probability of target attainment (PTA) for pharmacokinetic/pharmacodynamics (PK/PD) ratios associated with clinical efficacy and with the appearance of antimicrobial resistance for fluoroquinolones at each minimum inhibitory concentration (MIC) or mutant prevention concentration (MPC) were calculated, respectively. The cumulative fraction of response (CFR) was calculated for the three posology regimens against App and they ranged from 91.12% to 96.37% in weaners and from 93% to 97.43% in fatteners, respectively. In the case of Hp, they ranged from 80.52% to 85.14% in weaners and from 82.01% to 88.49% in fatteners, respectively. Regarding the PTA of the PK/PD threshold associated with the appearance of antimicrobial resistance, results showed that marbofloxacin would prevent resistances in most of the animals up to the MPC value of 1 μg/mL.