Control of methylxanthines in the competition horse: pharmacokinetic/pharmacodynamic studies on caffeine, theobromine and theophylline for the assessment of irrelevant concentrations.
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.
Center for Preventive Doping Research - Institute of Biochemistry, German Sport University Cologne, Cologne, Germany.
Marc
M
Machnik
Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.
Simone
S
Kaiser
Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.
Sophie
S
Koppe
Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.
Manfred
M
Kietzmann
Center for Preventive Doping Research - Institute of Biochemistry, German Sport University Cologne, Cologne, Germany.
Ina
I
Schenk
German Equestrian Federation, Warendorf, Germany.
Michael
M
Düe
Center for Preventive Doping Research - Institute of Biochemistry, German Sport University Cologne, Cologne, Germany.
Mario
M
Thevis
Center for Preventive Doping Research - Institute of Biochemistry, German Sport University Cologne, Cologne, Germany.
Wilhelm
W
Schänzer
Department of Experimental Physiopathology and Toxicology, National Veterinary School of Toulouse, Toulouse, France.
Pierre-Louis
PL
Toutain
D000818:Animals; D002110:Caffeine / Q000032:analysis / Q000737:chemistry* / Q000493:pharmacokinetics*; D002853:Chromatography, Liquid / Q000379:methods; D006736:Horses; D013805:Theobromine / Q000032:analysis / Q000737:chemistry* / Q000493:pharmacokinetics*; D013806:Theophylline / Q000032:analysis / Q000737:chemistry* / Q000493:pharmacokinetics*; D014970:Xanthines / Q000737:chemistry / Q000493:pharmacokinetics*
D014970:Xanthines; C008514:methylxanthine; D002110:Caffeine; D013806:Theophylline; D013805:Theobromine
LC-MS/MS; doping control; horse; international residue limits; methylxanthines, irrelevant concentrations