Control of methylxanthines in the competition horse: pharmacokinetic/pharmacodynamic studies on caffeine, theobromine and theophylline for the assessment of irrelevant concentrations

Abstract

Methylxanthines positives in competition samples have challenged doping control laboratories and racing jurisdictions since methylxanthines are naturally occurring prohibited substances and often constituents of feed. For theobromine, an international threshold (renamed in International Residue Limit, IRL) of 2 µg/mL in urine has been established. On the basis of the data presented herein, a threshold or rather an IRL for theobromine in plasma of 0.3 µg/mL was proposed and was thereupon approved by the International Federation of Horseracing Authorities (IFHA). Official recommendations for reporting caffeine and theophylline are still lacking. The aim of the study was to investigate IRLs for theobromine in blood and for caffeine and theophylline in blood and urine. Therefore, a set of six administrations were carried out including both single i.v. and single oral administrations of caffeine, theobromine and theophylline. Plasma and urine concentrations were determined using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS). Applying the Toutain model approach an effective plasma concentration (EPC) of caffeine was estimated at 3.05 µg/mL, irrelevant concentrations in blood (IPC) and urine (IUC) approached 6 and 12 ng/mL, respectively. EPC of theobromine was calculated with 3.80 µg/mL, and irrelevant concentrations of theobromine were determined at 8 ng/mL in plasma and at 142 ng/mL in urine. Toutain modelling of the theophylline data produced an EPC, IPC, and IUC of 3.20 µg/mL, 6 ng/mL, and 75 ng/mL, respectively. The obtained irrelevant concentrations were used to postulate IRLs for theobromine in plasma and for caffeine and theophylline in plasma and urine. Copyright © 2016 John Wiley & Sons, Ltd.

Systematic analysis to assess the scientific validity of the international residue limits for caffeine and theophylline in horse‐racing

“…The IRL for cafeine of 50 ng/ml urine is in accordance with the IUC of 14 ng/ml calculated in this study. This IUC is almost equal to the IUC of 12 ng/ml calculated by Machnik et al 21 These concentrations are much lower than those expected ater the administration of the HNED (2-2.5 mg/kg) in horses. 1 22 As shown by Fredholm, 23 adenosine receptors in the brain are the main pharmacological targets of cafeine within the therapeutic concentration range in human beings and animals.…”

“…Paraxanthine is a major metabolite of both cafeine and theophylline and can be present in the urine of horses at higher concentrations than the original substances. 21 It exhibits stimulatory efects similar or stronger than cafeine in laboratory animals 39 and human beings, 40 and is therefore classiied as a prohibited substance in horse-racing and equine sports. Currently, no IRL or analytic cut-of has been published for paraxanthine.…”

Plant-Derived Antioxidants Protect the Nervous System From Aging by Inhibiting Oxidative Stress

“…The main derivatives of astragalus are methylxanthine, theophylline (1,3-dimethylxanthine), theobromine (3,7-dimethylxanthine), and caffeine (1,3,7-trimethylxanthine) ( Li et al, 2017 ). Caffeine is considered to be a more beneficial derivative of astragalus to humans ( Machnik et al, 2017 ) and can excite the central nervous system. Therefore, proper caffeine intake can be very beneficial to the nervous system in general ( Cappelletti et al, 2015 ).…”

Advances in equine anti‐doping

“…On the ‘small molecule’ front these cover in vitro phase I metabolic studies of the selective estrogen receptor modulators (SERMs) tamoxifen and toremifene, and population studies of 5‐Aminoimidazole‐4‐carboxamide ribonucleotide (AICAR) in the horse . Equine pharmacokinetic studies are well represented with a focus on methylxanthines, betamethasone, and meldonium …”

“…On the 'small molecule' front these cover in vitro phase I metabolic studies of the selective estrogen receptor modulators (SERMs) tamoxifen and toremifene, [7] and population studies of 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) in the horse. [8] Equine pharmacokinetic studies are well represented with a focus on methylxanthines, [9] betamethasone, [10] and meldonium. [11] Recent progress in inductively coupled plasma mass spectrometry (ICP-MS) analysis is highlighted by the large-scale collaborative work of Popot et al [12] presenting interlaboratory reproducibility for the measurement of cobalt in equine urine and plasma.…”