Pharmacokinetic/pharmacodynamic evaluation of the efficacy of flumequine in treating colibacillosis in turkeys

Flumequine (FLU) is used in the treatment of systemic bacterial infections in poultry, including colibacillosis, which is a common disease in turkeys. The pharmacokinetic (PK) behavior of FLU administered to 32 healthy turkeys as an oral bolus via gavage or as 10-h pulsed administration in drinking water were compared, using the authorized dose of 15 mg/kg and the double dose of 30 mg/kg. The minimum inhibitory concentrations (MIC) of 235 Escherichia coli field strains isolated from poultry were determined for pharmacodynamics (PD) to develop a PK/PD model. Blood samples were collected at established times over 24 h, and the obtained plasma was analyzed using a liquid chromatography tandem mass spectrometry method that was validated in-house. A monocompartmental model and a noncompartmental model were applied to the data to obtain the PK results. For both types of administration and both dosages, the ratios of the maximum concentration (Cₘₐₓ)/MIC₅₀ and the area under the plasma concentration-time curve (AUC)/MIC₅₀ achieved were considerably lower than the fluoroquinolone breakpoints usually adopted for efficacy. The Cₘₐₓ/MIC₅₀ and AUC₀–₂₄/MIC₅₀ ratios were, respectively, 0.67 ± 0.09 and 4.76 ± 0.48 and 1.18 ± 0.35 and 7.05 ± 2.40 for the 15 and 30 mg/kg bolus doses, respectively. After 10-h pulsed administration of 15 mg/kg, values of Cₘₐₓ/MIC₅₀, 0.19 ± 0.02 on d 1 and 0.30 ± 0.08 on d 5 of therapy were obtained, the AUC/MIC₅₀ ratios were 2.09 ± 0.29 and 3.22 ± 0.93 on d 1 and 5, respectively. Higher values were obtained with the doubled dose of 30 mg/kg: the Cₘₐₓ/MIC₅₀ ratios were 0.49 ± 0.11 on d 1 and 0.69 ± 0.18 on d 5; the AUC/MIC₅₀ ratios were 5.15 ± 1.15 and 6.57 ± 1.92 on d 1 and 5, respectively. Based on these results, FLU administration should be adopted when specific diagnostic findings indicate its efficacy, and revising the dosage scheme to comply with the prudent and responsible use of antimicrobials in veterinary medicine is advisable.