Determination by HPLC with electrochemical detection of formoterol RR and SS enantiomers in urine

A method is described for the determination of the R,R- and S,S-enantiomer of the long-acting beta 2-adrenoceptor agonist formoterol, which is marketed as a racemate for the treatment of asthma. The methodology is a modification of a previously published assay for formoterol. The sample clean-up from urine takes place by liquid liquid extraction followed by solid phase extraction. An AGP-column combined with electrochemical detection is used for the separation and detection of the enantiomers. A diastereomer of formoterol (R,S- or S,R- configuration) is used as internal standard. The lower limits of detection of R,R-formoterol and S,S-formoterol were 60 and 75 pmol/L respectively. The method was validated by a cross-check of spiked urine samples with a GC/MS method for ''racemic'' formoterol (correlation of the sum of the enantiomers measured by HPLC with GC/MS results: r=0.999, n=17). The method appears to be well suited for pharmacokinetic studies of formoterol enantiomers in human subjects after inhalation of therapeutic doses of formoterol.