Abstract
Aim: The aim of the study was to investigate pharmacokinetics of terbutaline after oral and inhaled administration in healthy trained male subjects in relation to doping control.Methods: Twelve healthy well-trained young men (27 ±2 years; mean ± SE) underwent two pharmacokinetic trials that compared 10 mg oral terbutaline with 4 mg inhaled dry powder terbutaline. During each trial, subjects performed 90 min of bike ergometer exercise at 65% of maximal oxygen consumption. Blood (0–4 h) and urine (0–24 h) samples were collected before and after administration of terbutaline. Samples were analyzed for concentrations of terbutaline by high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS).Results: Pharmacokinetics differed between the two routes of administration. Serum Cmax and area under the serum concentration-time curve (AUC) were lower after oral administration compared to inhalation (Cmax: 4.2 ± 0.3 vs. 8.5 ± 0.7 ng/ml, P ≤ 0.001; AUC: 422 ± 22 vs. 1308 ± 119 ng/ml × min). Urine concentrations (sum of the free drug and the glucuronide) were lower after oral administration compared to inhalation 2 h (1100 ± 204 vs. 61 ± 10 ng/ml, P ≤ 0.05) and 4 h (734 ± 110 vs. 340 ± 48 ng/ml, P ≤ 0.001) following administration, whereas concentrations were higher for oral administration than inhalation 12 h following administration (190 ± 41 vs. 399 ± 108 ng/ml, P ≤ 0.05). Urine excretion rate was lower after oral administration than inhalation the first 2 h following administration (P ≤ 0.001). Systemic bioavailability ratio between the two routes of administration was 3.8:1 (inhaled: oral; P ≤ 0.001).Conclusion: Given the higher systemic bioavailability of inhaled terbutaline compared to oral, our results indicate that it is difficult to differentiate allowed inhaled use of terbutaline from prohibited oral ingestion based on urine concentrations in doping control analysis. However given the potential performance enhancing effect of high dose terbutaline, it is essential to establish a limit on the WADA doping list.
Highlights
The prevalence of asthma and exercise-induced bronchoconstriction is high in the athletic population (Carlsen et al, 2008; Fitch et al, 2008; Price et al, 2014; Couto et al, 2015)
In 2014, β2-agonists accounted for 4% (122/3079) of analytical finding (AAF) reported by World Anti-Doping Agency (WADA) accredited doping control laboratories
Of the 122 AAFs involving β2-agonists in 2014, terbutaline accounted for 76%, whereas salbutamol and formoterol only accounted for 12% together (The World Anti-Doping Agency, 2014a)
Summary
The prevalence of asthma and exercise-induced bronchoconstriction is high in the athletic population (Carlsen et al, 2008; Fitch et al, 2008; Price et al, 2014; Couto et al, 2015). The prevalence has been reported to be as high as 30–50% (Parsons and Mastronarde, 2005; Aavikko and Helenius, 2012) compared to the general population prevalence of ∼5% in Western countries (Elers et al, 2012a). Use of β2-agonists in competitive sport is restricted by anti-doping regulations in accordance with the World Anti-Doping Agency’s (WADA) list of prohibited substances (The World Anti-Doping Agency, 2015b). The 2016-list of prohibited substances restricts use of all β2-agonists except for therapeutic inhalation of salbutamol, formoterol, and salmeterol (The World Anti-Doping Agency, 2016). Of the 122 AAFs involving β2-agonists in 2014, terbutaline accounted for 76%, whereas salbutamol and formoterol only accounted for 12% together (The World Anti-Doping Agency, 2014a)
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