A study to compare circulating flunixin, meloxicam and gabapentin concentrations with prostaglandin E2 levels in calves undergoing dehorning

The purpose of this study was to investigate the pharmacokinetics of intravenous flunixin (2.2 mg/kg b.w.), oral meloxicam (1 mg/kg b.w.), oral gabapentin (15 mg/kg b.w.) alone or co-administrated with meloxicam as well as the effects of these compounds on prostaglandin E-2 (PGE(2)) synthesis in calves subjected to surgical dehorning. Plasma samples collected up to 24 h after drug administration were analyzed by liquid chromatography/mass spectrometry, whereas blood PGE(2) levels were measured by immunoenzymatic assay. In plasma, the terminal half-live of flunixin, meloxicam and gabapentin were 6.0 h (range, 3.4-11.0 h), 16.7 h (range, 13.7-21.3 h) and 15.3 h (range, 11-32.9 h), respectively. The co-administration of single doses of gabapentin and meloxicam did not seem to affect the pharmacokinetic profile of the two drugs except for gabapentin that reached significantly (P < 0.05) higher maximum serum concentration (C-max) when co-administered with meloxicam, than when administered alone. At 5, 360 and 720 min after dehorning, a significant (P < 0.01) decrease in PGE(2) concentration was observed in flunixin-treated animals compared with control calves. Moreover, circulating log PGE(2) concentrations were inversely proportional to log flunixin concentrations (R-2 = 0.75; P < 0.0001). None of the other drugs significantly affected blood PGE(2) levels. Further assessment of oral meloxicam and gabapentin in established pain models is required to formulate science based analgesic recommendations to enhance animal well-being after dehorning. (c) 2013 Elsevier Ltd. All rights reserved.