THRESHOLD LEVEL FOR THEOPHYLLINE IN DOPING ANALYSIS

HPLC in the reversed-phase mode is used to assay methylxanthines inclu ding theobromine, paraxanthine, theophylline and caffeine in urine. Th e calibration graphs show good linearity in the concentration range 0- 10 mu g/ml. The limit for accurate quantitation of theophylline was 0. 25 mu g/ml. Between 6 and 20% of the parent drug is recovered in urine (0-12 h) after the oral administration of sustained release preparati ons containing 150 and 250 mg theophylline to four volunteers. Theophy lline levels above 0.25 mu g/ml were found in 1539 out of 3885 urine s amples collected from athletes during unannounced doping control in Fl anders. Statistical evaluation of the results gives a far outside valu e [75th percentile+(3x interquartile range)] of 2.25 mu g/ml. The rati o theophylline paraxanthine (TP/PX) as an indicator for the non-dietar y intake of theophylline seems to be more reliable. The far outside ra tio was 0.20. To ensure with the greatest possible degree of certainty that no false-positive result is reported, decision limits of 5 mu g/ ml and 0.50, for theophylline and the ratio TP/PX respectively, are pr oposed.