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Discrimination of Prohibited Oral Use of Salbutamol from Authorized Inhaled Asthma Treatment

¹ Pharmacology Research Unit, Institut Municipal d’Investigació Mèdica (IMIM), Doctor Aiguader 80, 08003 Barcelona, Spain.

² Department of Human Movement & Exercise Science, University of Western Australia, Perth, Australia 6907.

³ Universitat Pompeu Fabra, 08005 Barcelona, Spain.

⁴ Universitat Autònoma de Barcelona, Barcelona, Spain.
^a Author for correspondence. Fax 34-93-2213237; e-mail jsegura{at}imim.es

Background: The administration of salbutamol is permitted only by inhalation by the International Olympic Committee (IOC) for the management of asthma and exercise-induced asthma in athletes. The establishment of criteria to distinguish between the IOC authorized use (inhaled) and the IOC prohibited use (oral) of salbutamol appeared possible using simultaneous evaluation of variables based on the concentration of nonconjugated enantiomers of salbutamol excreted in urine.

Methods: Urine was collected from asthmatic and nonasthmatic swimmers who had received various preexercise doses of oral (five doses of 4 mg) or inhaled (two doses of 100 µg) salbutamol. Urine was also obtained from subjects who had received the maximum dosage of inhaled salbutamol advisable for competing athletes to provide protection from exercise-induced asthma and treatment of asthma (1600 µg in 24 h, 800 µg being in the last 4 h). All samples were analyzed to determine the total amount of unchanged salbutamol excreted in urine and the ratio between the S and R enantiomers.

Results: The discriminant function D = -3.776 + 1.46 x 10^-3 {[S(+)] + [R(-)]} + 1.012 {[S(+)]/[R(-)]} can be used to classify data into two groups, inhaled and oral. The confirmatory criterion suggested (cutoff at D = 1.06, 4 SD from the mean D value of the inhaled distribution) has been verified in different sets of samples showing suspicious concentrations by conventional screening procedures in doping control. An 11.8% false-negative (oral classified as inhaled) rate is assumed with the confirmatory criterion proposed, but virtually no false positives (inhaled classified as oral) are obtained (<1 in 33 000).

Conclusions: The overall procedure recommended is to screen all samples and to apply the confirmation criterion proposed to samples showing free racemic salbutamol concentrations >500 µg/L by gas chromatography-mass spectrometry or free + conjugated racemic salbutamol concentrations >1400 µg/L by ELISA.

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