title: Pharmacokinetics of Oral and Inhaled Terbutaline after Exercise in Trained Men.
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Respiratory Research Unit, Bispebjerg Hospital Copenhagen, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Dyreborg
authors.affiliation: Respiratory Research Unit, Bispebjerg Hospital Copenhagen, Denmark.
authors.forename: Nanna
authors.initials: N
authors.lastname: Krogh
authors.affiliation: Respiratory Research Unit, Bispebjerg HospitalCopenhagen, Denmark; IOC Sports MedicineCopenhagen, Denmark.
authors.forename: Vibeke
authors.initials: V
authors.lastname: Backer
authors.affiliation: Norwegian Doping Control Laboratory, Oslo University Hospital Oslo, Norway.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Rzeppa
authors.affiliation: Norwegian Doping Control Laboratory, Oslo University Hospital Oslo, Norway.
authors.forename: Peter
authors.initials: P
authors.lastname: Hemmersbach
authors.affiliation: Respiratory Research Unit, Bispebjerg HospitalCopenhagen, Denmark; IOC Sports MedicineCopenhagen, Denmark; Department of Nutrition, Exercise, and Sports, University of CopenhagenCopenhagen, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Hostrup
keywords: WADA; asthma; doping analysis; pharmacology; β2-agonist