In vivo activity of cefquinome against Riemerella anatipestifer using the pericarditis model in the duck

Cefquinome is a fourth‐generation cephalosporin with broad‐spectrum antibacterial activity, including activity against enteric gram‐negative bacilli such as Riemerella anatipestifer. The pericarditis model was used to examine the pharmacodynamic characteristics of cefquinome against R. anatipestifer. Serum levels of cefquinome following the administration of different doses were determined by LC‐MS/MS. Ducks with ca. 10⁶ CFU/mL at the initiation of therapy were treated with cefquinome at doses that ranged from 0.0156 to 2 mg/kg of body weight/day (in 3, 6, 12, or 24 divided doses) for 24 h. The percentage of a 24‐h dosing interval that the unbound serum cefquinome concentrations exceeded the MIC (fT > MIC) were the pharmacokinetic (PK)–pharmacodynamic (PD) parameter that best correlated with efficacy (R² 86.3% for R. anatipestifer, compared with 58.9% for the area under the concentration–time curve/MIC and 10.6% for peak/MIC). A sigmoid E_max model was used to estimate the magnitudes of the %fT > MIC associated with net bacterial stasis, a 1‐log₁₀ CFU reduction from baseline, and a 2‐log₁₀ CFU reduction from baseline; the corresponding values were (22.5 ± 1.3) %, (35.2 ± 4.5) %, and (42.4 ± 2.7) %. These data showed that treatment with cefquinome results in marked antibacterial effects in qvivo against R. anatipestifer and that the host's immunity may also play a key role in the anti‐infective therapy process.