A new option for pain relief in donkeys: a pharmcokinetic pilot study comparing transdermal Flunixin Meglumine to oral and intravenous forms

Introduction

Donkeys are stoic animals who may endure pain without displaying feelings and complaints. Due to this behavior, donkeys may ultimately mask pain with behaviors, such as sham eating or by only showing slight indications of pain. These subtle behaviors may go unnoticed, thus concealing illness/injury. There’s a lack of analgesic drugs with marketing authorization for administration to donkeys and lack of information on dosing rates and intervals when analgesia is provided. Donkeys differ from horses behaviorally, physiologically, and pharmacologically1. Recent approval and effectiveness of transdermal flunixin meglumine in cattle has opened the door for the drug’s potential application in other species. Hypothesis was transdermal flunixin meglumine will have similar pharmacokinetics and effects on biomarkers of inflammation in donkeys compared to oral and injectable.

Materials And Methods

Oral, injectable, and transdermal flunixin meglumine (Banamine®, Merck Animal Health) were administered to six healthy donkeys dosed at 1.1 mg/kg BW for oral, intravenous and (per label) 3.3 mg/kg transdermal in a three-way crossover design. The study was carried out in Davis, California, U.S.A IACUC #22018. Whole blood samples were collected over 96 hours to measure concentrations of flunixin, 5OH flunixin, and eicosanoids using LC-MS/MS and pharmacokinetic parameters determined.

Results

Both flunixin and 5OH flunixin reached detectable levels in blood collected during transdermal trial. Drug elimination was slower following transdermal compared to IV and oral forms. Transdermal significantly decreased TXB2 1 to 96 hours post-administration, IV and oral resulted in TXB2 reduced 1 to 8 hours (P<0.001). Significant reduction in PGF2 alpha was seen 1 hour later in oral and IV but transdermal resulted in gradual decline 1 to 24 hours.

Discussion

This study suggested therapeutic doses for flunixin are 1.1mg/kg for oral and IV and 3.3 mg/kg off label use of transdermal are effective.

References

1. Ciofalo VB, Latranyi MB, Patel JB, et al. Flunixin meglumine: a non-narcotic analgesic. Pharmacol. Exp. Ther. 1977, 200(3), 501-507.