Equine Vet J. 2021 Oct 30. doi: 10.1111/evj.13532. Online ahead of print.
ABSTRACT
BACKGROUND: For medication control in several jurisdictions, withdrawal time is the period of refrain from racing after drug administration. It is set by adding a safety period to an experimental detection time. However, there are no reports of statistical analyses of detection time for the determination of withdrawal time in flunixin meglumine-treated horses.
OBJECTIVE: To analyse the population pharmacokinetics of flunixin in horses through the generation of a dataset for detection time statistical analysis and predictions via Monte Carlo simulation.
STUDY DESIGN: Experimental study.
METHODS: Drug plasma and urine concentrations following single intravenous (i.v.) administration of flunixin 1.1 mg/kg bodyweight (BW) in 10 horses and multiple administration of q 24 h for 5 days in 10 horses were measured using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Data were modelled using a nonlinear mixed effect model followed by Monte Carlo simulation. Irrelevant plasma concentration (IPC) and irrelevant urine concentration (IUC) were calculated using the Toutain approach. Detection times were obtained considering the time after the last administration for selected quantiles of 5000 hypothetical horses under the International Screening Limit (ISL) proposed by the International Federation of Horseracing Authorities (plasma: 1 ng/ml, urine; 100 ng/ml) RESULTS: For a regimen of 1.1 mg/kg BW q 24 h, the IPC and IUC values were 2.0 and 73.0 ng/ml, respectively. Detection times in plasma above the ISL for 90% of simulated horses were estimated as 74 h after a single 1.1 mg/kg dose administration, 149 h and 199 h after multiple doses over 5 days at either 24- or 12-h intervals, respectively. Corresponding detection times in urine were 46 h, 68 h and 104 h, respectively.
MAIN LIMITATION: Only female horses were investigated.
CONCLUSIONS: Statistical detection times for different flunixin meglumine regimens indicated a delay of detection time in plasma after multiple administrations under ISL.
PMID:34719043 | DOI:10.1111/evj.13532
