A GLP tissue residue depletion study in sheep following oral / buccal administration of meloxicam

Summary

Various forms of surgical husbandry procedures are necessary in sheep under good animal husbandry practices.  Animal welfare, in particular pain management, following surgical husbandry procedures has evolved into a political issue that could impact the Australian sheep meat and sheep wool industries.  While alternate technologies are developed to minimise invasive procedures, there will always be a need for non-steroidal anti-inflammatory drug (NSAID) therapy in sheep and currently, no NSAID is registered in Australia for use in this species.  Any use of NSAIDs in sheep is ‘off-label’.  The additional issue is that NSAID therapy is currently administered by injection.  This is undesirable from an on-farm occupational health and safety risk minimisation perspective.
Meloxicam, an oxicam derivative, is a selective cyclooxygenase-2 inhibitor and potent NSAID.  It is used as a veterinary drug for dogs, cats, cattle, pigs and horses either as an injectable solution or oral suspension.  
Buccal administration of specifically formulated medications can result in rapid absorption.  Comparison of the bioavailability of oral and buccal meloxicam formulations administered to sheep showed that high serum levels of meloxicam were detected within 8 minutes of buccal dosing.  These levels approximate reported therapeutic levels in other species.           
A residue depletion study was required to establish a meat withholding period (WHP) and export slaughter interval (ESI) to satisfy product registration requirements.  The GLP (Good Laboratory Practice) study described in this report determined the meloxicam tissue residue depletion profile in sheep following buccal administration of a meloxicam formulation (10 mg meloxicam/mL) at the maximum proposed dose rate of 1 mg meloxicam per kg bodyweight.
The study complied with national and international standards such as the OECD’s Series on Principles of Good Laboratory Practice and Compliance Monitoring; APVMA RGL23 and VICH GL1 and GL49.
Forty sheep were randomly allocated to 8 groups (six groups of 6 and two groups of 2) One of the groups of 2 acted as the untreated control group, the other contained treated spares.  Sheep were treated with the test formulation according to individual bodyweight at a dose rate of 1mg meloxicam/kg bodyweight and sacrificed at pre-determined time intervals.  Following euthanasia, muscle, liver, kidney, peri-renal fat and masseter muscle (treatment side) tissue samples were collected, processed, frozen and sent for analysis.
Analysis of meloxicam in ovine tissues was performed using a validated liquid chromatography – tandem mass spectrometry (LC/MS/MS) method.  Sample preparation was based on acidic hydrolysis prior to neutralisation.  Following addition of an internal standard and extraction into an organic solvent by salt-induced liquid-liquid partitioning the samples were analysed by LC/MS/MS.
The analytical methodology had a validated limit of quantitation (LOQ) of 5.0 µg/kg.  A limit of detection (LOD) of 1.08 µg/kg, 1.26 µg/kg1.29 µg/kg, 1.29 µg/kg and 1.76 µg/kg was established for liver, kidney, muscle, masseter muscle and peri-renal fat respectively.  The results showed that there were no detectable residues for meloxicam in any tissue matrix from (and inclusive of) Day 10 onwards post-treatment.