Factors affecting pharmacokinetics of inhaled salbutamol in athletes: Application of 4O sulfate metabolite analysis to improve predictive value of AAFs

Code: 18C08MH

Salbutamol is a short-acting beta2-agonist used for asthma and exercise induced bronchoconstriction and is permitted in inhaled doses up to 1600 μg in 24 h, not exceeding 800 μg in 12 h. A corresponding urine threshold of 1000 ng/mL and decision limit of 1200 ng/mL has been established to discriminate permitted inhalation from prohibited misuse. If an athlete exceeds the decision limit in doping control, this is recorded as an Adverse Analytical Finding (AAF) that may result in the athlete being charged with an anti-doping violation.

While salbutamol has been available for half a century, knowledge about its pharmacokinetics in relation to athletes and anti-doping control is incomplete. A handful of clinical trials underpin that high urine concentrations of salbutamol, relative to the dose inhaled, can occur, indicating that the risk of AAFs reported for salbutamol is possibly greater than previously assumed. These observations are further substantiated by the fact that several supplements and medications may interfere with the metabolism and subsequent excretion of salbutamol, which to our knowledge, are unexplored with respect to the salbutamol decision limit. Thus, athletes are exposed to several factors that may affect the pharmacokinetics of inhaled salbutamol, including, but not limited to strenuous exercise, dehydration, diet and supplements, and other medication.

This project will provide a comprehensive investigation into the factors that affect the intra- and inter-individual pharmacokinetics of salbutamol in female and male athletes. The primary objective is to model the peak urine excretion rate and peak urine concentrations of unchanged salbutamol and its major 4'O sulfate metabolite after permitted inhalation and prohibited oral ingestion to possibly improve the predictive value and accuracy of the decision limit for salbutamol.

Main Findings

The 2021 Prohibited List allows athletes to administer salbutamol at inhaled doses up to 1600 µg in 24 hours, not exceeding 800 µg in 12 hours. A urine threshold of 1000 ng/mL with a corresponding decision limit of 1200 ng/mL has been established to discriminate permitted therapeutic use from prohibited supratherapeutic use during doping control. Despite many studies investigating the pharmacokinetics of salbutamol, limited data are available on factors that may confound its pharmacokinetics. In this project, we investigated the effect of dietary flavonoid intake, dehydration, combined flavonoid intake and dehydration, and consecutive days of salbutamol inhalation on urine pharmacokinetics in highly trained females and males who were subjected to prolonged strenuous exercise. Additionally, we evaluated the diagnostic performance of the current threshold and decision limit in discriminating permitted inhaled doses (1600 µg in 24 hours) from prohibited oral doses of 8 mg salbutamol. In this comprehensive repeated measures study, we collected and analyzed more than 750 urine samples and demonstrated that the current decision limit approach, whereby concentrated urine samples are adjusted to a specific gravity (SG) of 1.020, has robust sensitivity and specificity for application in doping control. Only 1 sample, collected from a female participant following consecutive days of inhalation, exceeded the decision limit after SG-adjustment (reaching 1303 ng/mL), and only 4 samples (from 3 different participants; also all from consecutive days of inhalation) exceeded the threshold with SG adjustment. As such, employing SG-adjusted data from 0-6 h at all trials, which is the most relevant window of detection, sensitivity at the decision limit was 40% with 99% specificity, while at the threshold, sensitivity was 47% with 98% specificity. Females generally presented with higher urine concentrations of salbutamol than males, and 3 of the 4 samples exceeding the threshold were from female participants. Consecutive days of inhalation resulted in higher urine concentrations of salbutamol, indicating that 24 hours are insufficient for complete urine 2 elimination of salbutamol for most individuals. Prior bioflavonoid intake lowered urine concentrations of salbutamol after inhalation, while dehydration, as expected, led to higher urine concentrations of salbutamol which could be accounted for with SG adjustment. In conclusion, the current threshold approach with SG adjustment displays robust sensitivity and specificity, even in the face of dehydration, bioflavonoid intake, and consecutive days of treatment. Female athletes generally present with higher urine concentrations than male athletes.