Evaluation of different PK/PD ratios of three enrofloxacin preparations on the clinical response of pneumonic calves.

Importance: Enrofloxacin preparations are available for administration daily or every 3 days. This study presents clinical evidence to define which preparation is adequate to treat clinical cases of bovine respiratory disease (BRD) in calves.

Objective: To correlate the pharmacokinetics/pharmacodynamics (PK/PD) ratios of three pharmaceutical preparations of enrofloxacin with their clinical efficacy in treating BRD.

Methods: The PK/PD ratios of three enrofloxacin preparations were determined in healthy calves. Then, 48 BRD-affected calves initially treated IV with 2.2 mg/kg of flunixin-meglumine, were randomly assigned to treatment with: enrofloxacin dihydrate-hydrochloride (enro-C) 10% water suspension daily (10 mg/kg subcutaneous for three to six days); enro-C with alginate (enro-C/Al), and reference enrofloxacin (enro-R), both intended for treatment every 72-h in two occasions (10 mg/kg).

Results: The highest maximum plasma concentration (Cmax)/minimum inhibitory concentration (MIC) ratio was obtained with enro-C and the highest area under the curve (AUC)₀₋₇₂/MIC ratio with enro-R, and enro-C/Al exhibited an AUC₀₋₇₂/MIC smaller, but Cmax/MIC higher than enro-R. Based on repeated statistical measurements, clinical progress revealed that the best outcomes were observed with enro-C ( < 0.05), and no statistical differences resulted by comparing enro-C/Al with enro-R.

Conclusions And Relevance: If the priority in calves affected by BRD is to speed up their recovery, and despite the more significant amount enro-C injected, using of lower doses of enrofloxacin as in the long-acting preparations is unsustainable. This study demonstrates that the clinical efficacy of enrofloxacin in cattle is optimally linked to Cmax/MIC rather than to AUC/MIC, which occurs better when injecting enro-C.