Enantioselective disposition of (R,R)-formoterol, (S,S)-formoterol and their respective glucuronides in urine following single inhaled dosing and application to doping control

Formoterol is a long‐acting beta2‐adrenoceptor agonist (LABA) used for treatment of asthma and exercise‐induced bronchoconstriction. Formoterol is usually administered as a racemic (rac‐) mixture of (R,R)‐ and (S,S)‐enantiomers. While formoterol is restricted by the World Anti‐Doping Agency (WADA), inhalation of formoterol is permitted to a predetermined dose (54 μg/24 hours) and a urine threshold of 40 ng/mL. However, chiral switch enantiopure (R,R)‐formoterol is available, effectively doubling the therapeutic advantage for the same threshold. The aim of this study was to investigate whether formoterol exhibits enantioselective urinary pharmacokinetics following inhalation. Six healthy volunteers were administered a 12 μg inhaled dose of rac‐formoterol. Urine was collected over 24‐hours and analysed by enantioselective UPLC‐MS/MS assay. Total (free drug plus conjugated metabolite) median (min‐max) rac‐formoterol urine levels following inhalation were 1.96(1.05‐13.4) ng/mL, 1.67(0.16‐9.67) ng/mL, 0.45(0.16‐1.51) ng/mL, 0.61(0.33‐0.78) ng/mL, and 0.17(0.08‐1.06) ng/mL at 2, 4, 8, 12 and 24 hours, respectively, well below the 2019 urine threshold. The proportion of conjugation differed between enantiomers with glucuronide conjugation much greater for (R,R)‐formoterol (around 30‐60% of total) compared to (S,S)‐formoterol (0‐30%). There was clear evidence of inter‐individual enantioselectivity observed in the ratios of (R,R):(S,S)‐formoterol, where (S,S)‐ was predominant in free formoterol, and (R,R)‐ predominant in the conjugated metabolite. In conclusion, rac‐formoterol delivered by inhalation exhibits enantioselective elimination in urine following single dose administration. Enantioselective assays should be employed in doping control to screen for banned beta2‐agonist chiral switch products such as (R,R)‐formoterol, and total hydrolysed rac‐formoterol is warranted to account for inter‐individual differences in enantioselective glucuronidation.