AUTOMATED AND SENSITIVE METHOD FOR THE DETERMINATION OF FORMOTEROL INHUMAN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND ELECTROCHEMICAL DETECTION

An automated high-performance liquid chromatography (HPLC) method for the determination of formoterol in human plasma with improved sensitiv ity has been developed and validated. Formoterol and CGP 47086, the in ternal standard, were extracted from plasma (1 ml) using a cation-exch ange solid-phase extraction (SPE) cartridge. The compounds were eluted with pH 6 buffer solution-methanol (70:30, v/v) and the eluate was fu rther diluted with water. An aliquot of the extract solution was injec ted and analyzed by HPLC. The extraction, dilution, injection and chro matographic analysis were combined and automated using the automate (A SPEC) system. The chromatographic separations were achieved on a 5 mu m, Hypersil ODS analytical column (200 mmx3 mm I.D.), using (pH 6 phos phate buffer, 0.035 M+20 mg/l EDTA)-MeOH-CH3CN (70:25:5, v/v/v) as the mobile phase at a flow-rate of 0.4 ml/min. The analytes were detected with electrochemical detection at an operating potential of +0.63 V. Intra-day accuracy and precision were assessed from the relative recov eries of calibration/quality control plasma samples in the concentrati on range of 7.14 to 238 pmol/l of formoterol base. The accuracy over t he entire concentration range varied from 81 to 105%, and the precisio n (C.V.) ranged from 3 to 14%. Inter-day accuracy and precision were a ssessed in the concentration range of 11.9 to 238 pmol/l of formoterol base in plasma. The accuracy over the entire concentration range vari ed from 98 to 109%, and precision ranged from 8 to 19%. At the limit o f quantitation (LOQ) of 11.9 pmol/l for inter-day measurements, the re covery value was 109% and C.V. was 19%. As shown from intra-day accura cy and precision results, favorable conditions (a newly used column, a newly washed detector cell and moderate residual cell current level) allowed us to reach a LOQ of 7.14 pmol/l of formoterol base (3 pg/ml o f formoterol fumarate dihydrate). Improvement of the limit of detectio n by a factor of about 10 was reached as compared to the previously de scribed methods. The method has been applied for quantifying formotero l in plasma after 120 mu g drug inhalation to volunteers. Formoterol w as still measurable at 24 h post-dosing in most subjects and a slow el imination of formoterol from plasma beyond 6-8 h after inhalation was demonstrated for the first time thanks to the sensitivity of the metho d. (C) 1997 Elsevier Science B.V.