Effect of flunixin meglumine on the pharmacokinetics of enrofloxacin and marbofloxacin in preweaning calves.

Flunixin prolongs fluoroquinolone elimination in calves without compromising efficacy.

This pharmacokinetic study investigated potential drug interactions between flunixin meglumine (an NSAID) and two fluoroquinolone antibiotics (enrofloxacin and marbofloxacin) in preweaning dairy calves aged 20-30 days. Ten Holando Argentino calves received each antimicrobial alone and then co-administered with flunixin in a crossover design with 15-day washout periods. Plasma drug concentrations were measured over 24 hours using HPLC, and pharmacokinetic parameters were derived through non-compartmental analysis. Results demonstrated that flunixin meglumine significantly prolonged the elimination half-life of both fluoroquinolones without altering the area under the concentration-time curve. Additionally, flunixin reduced enrofloxacin's biotransformation to its active metabolite ciprofloxacin. Pharmacokinetic/pharmacodynamic target analysis showed adequate coverage against Pasteurella multocida and Histophilus somni but insufficient coverage for Mannheimia haemolytica and Mycoplasma bovis. The authors acknowledge limitations including the small sample size, use of healthy calves only, reliance on published MIC values, and plasma-based analysis. Clinically, the findings suggest flunixin co-administration extends fluoroquinolone elimination without compromising estimated efficacy in some bovine respiratory pathogens.

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