Pharmacokinetics of paracetamol in the Thoroughbred horse following an oral multi-dose administration.

Paracetamol is a widely used, non-opioid analgesic and antipyretic drug. Scientific evidence suggests that it is an effective pain treatment in equine medicine. However, there is very little published information about the pharmacokinetics of the drug in the horse. The aim of the research was to determine the pharmacokinetics of paracetamol in equine plasma and urine to inform treatment of Thoroughbred racehorses. In this multi-dose study, paracetamol was administered orally at 20 mg/kg to six Thoroughbred horses. Pre- and post-administration urine and plasma samples were collected and analysed using a quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Pharmacokinetic analysis of urine and plasma paracetamol clearance profiles was carried out, which enabled the calculation of possible screening limits (SL) that can regulate for a detection time of 120 h. Additionally, an estimation of orthocetamol concentration levels in urine was carried out to investigate any underlying relationship between the para- and ortho-isomers as both were suspected to contribute to basal levels, possibly due to environmental feed sources.

A novel mass spectrometry-based method for determining insulin-like growth factor 1: assessment in a cohort of subjects with newly diagnosed acromegaly.

OBJECTIVE: To develop an alternative method to immunoassay for the quantitative analysis of insulin-like growth factor 1 (IGF-1) using a mass spectrometry (MS)-based approach. STUDY DESIGN AND PATIENTS: A stable isotope dilution Ultra High Performance Liquid Chromatography tandem MS (uHPLC-MS/MS)-based method for the quantification of IGF-1 was developed. The method employed Selected Reaction Monitoring (SRM) of two tryptic peptides derived from IGF-1, and utilised solid phase extraction for enrichment of the peptide fraction containing IGF-1 rather than immunocapture, so was less susceptible to assay interference. Plasma samples from 25 consecutive unselected patients with newly diagnosed acromegaly, collected both before and after 24 weeks of primary medical therapy with Lanreotide Autogel(®), were analysed by a widely used commercial immunoassay (Siemens Immulite 2000(®)) and by uHPLC-MS/MS. RESULTS: The uHPLC-MS/MS method showed good correlation with the immunoassay over a wide range of IGF-1 concentrations. The Passing and Bablock regression was: uHPLC-MS/MS (nmol/l) = 1.37 (95% confidence interval: 1.26-1.46) × immunoassay (nmol/l) + 3.14 (95% confidence interval: -2.71 to 10.32). Six patients had discordant growth hormone (GH) and IGF-1 levels following primary medical therapy, and in all six the immunoassay and uHPLC-MS/MS platforms returned comparable results. The method was not affected by concentrations of IGFBP3 up to 12,500 ng/ml. CONCLUSIONS: uHPLC-MS/MS offers an independent method for determining/validating IGF-1 in subjects with acromegaly. Further studies, including the establishment of age- and sex-matched reference ranges and calibration to the new International IGF-1 standard IS 02/254, are now required to allow its introduction in to routine clinical use.

In vitro metabolism of tiletamine, zolazepam and nonbenzodiazepine sedatives: Identification of target metabolites for equine doping control.

Within horseracing, the detection of prohibited substance doping often requires urine analysis; hence, it is necessary to understand the metabolism of the drugs in question. Here, the previously unknown equine metabolism of eight sedatives is reported in order to provide information on target metabolites for use in doping control. Phase I metabolite information was provided by incubation with equine liver S9 fraction. In vitro techniques were chosen in order to reduce the ethical and financial issues surrounding the study of so many compounds, none of which are licensed for use in horses in the UK. Several metabolites of each drug were identified using liquid chromatography-high resolution mass spectrometric (LC-HRMS) analysis on an LTQ-Orbitrap. Further structural information was obtained by tandem mass spectrometry (MS/MS) analysis; allowing postulation of the structure of some of the most abundant in vitro metabolites. The most abundant metabolites of alpidem, etifoxine, indiplon, tiletamine, zaleplon, zolazepam, zolpidem, and zopiclone related to hydroxylation/N-oxidation, deethylation, demethylation, deethylation, hydroxylation/N-oxidation, demethylation, hydroxylation/N-oxidation and hydroxylation/N-oxidation, respectively. In many cases, further work would be required to fully elucidate the precise positioning of the functional groups involved. The results of this study provide metabolite information that can be used to enhance equine anti-doping screening methods. However, the in vitro metabolites identified are at present only a prediction of those that may occur in vivo. In the future, any positive findings of these drugs and/or their metabolites in horse urine samples could help validate these findings and/or refine the choice of target metabolites.