The development of a radioimmunoassay for formoterol

Assay for the determination of low dosage form of formoterol dry syrup by capillary electrophoresis with head-column field-amplified sample stacking

The development of a capillary zone electrophoresis method with head-column field-amplified sample stacking injection for the determination of formoterol (FMTR) in a low dosage dry syrup form was described. To obtain the highest sensitivity, the sample solution was prepared by high content of organic solvent with the presence of a small amount of H+ (60-100 microM) and the capillary inlet end was dipped in water before electroinjection. This method was fully validated in terms of repeatability (RSDs for migration time, peak area of FMTR and peak area ratio between FMTR and I.S. at 1 microg/ml of FMTR was 0.76, 1.10 and 0.55% respectively), reproducibility (RSDs from different capillaries, analytes, days and instruments were 1.52%, 1.04%, 1.16% and 1.93% respectively), linearity (y = 0.827x - 0.085, r = 0.9993 (n = 6) over the range of 0.25-2.0 microg/ml), limits of quantitation, ruggedness and robustness. The method was applied to the determination of the drug in commercial dry syrup preparation (recovery was 100.9%, RSD = 1.5%, n = 5) and proved to be fast and reliable for the quantitation analysis of FMTR in the pharmaceutical form.

Automated and sensitive method for the determination of formoterol in human 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 sensitivity has been developed and validated. Formoterol and CGP 47086, the internal standard, were extracted from plasma (1 ml) using a cation-exchange solid-phase extraction (SPE) cartridge. The compounds were eluted with pH 6 buffer solution-methanol (70:30, v/v) and the eluate was further diluted with water. An aliquot of the extract solution was injected and analyzed by HPLC. The extraction, dilution, injection and chromatographic analysis were combined and automated using the automate (ASPEC) system. The chromatographic separations were achieved on a 5 microm, Hypersil ODS analytical column (200 mm x 3 mm I.D.), using (pH 6 phosphate 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 recoveries of calibration/quality control plasma samples in the concentration range of 7.14 to 238 pmol/l of formoterol base. The accuracy over the entire concentration range varied from 81 to 105%, and the precision (C.V.) ranged from 3 to 14%. Inter-day accuracy and precision were assessed in the concentration range of 11.9 to 238 pmol/l of formoterol base in plasma. The accuracy over the entire concentration range varied from 98 to 109%, and precision ranged from 8 to 19%. At the limit of quantitation (LOQ) of 11.9 pmol/l for inter-day measurements, the recovery value was 109% and C.V. was 19%. As shown from intra-day accuracy 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 of formoterol fumarate dihydrate). Improvement of the limit of detection by a factor of about 10 was reached as compared to the previously described methods. The method has been applied for quantifying formoterol in plasma after 120 microg drug inhalation to volunteers. Formoterol was still measurable at 24 h post-dosing in most subjects and a slow elimination of formoterol from plasma beyond 6-8 h after inhalation was demonstrated for the first time thanks to the sensitivity of the method.

Enantioselective disposition of albuterol in humans

The study of enantioselective disposition of chiral drugs is important to provide a rationale of plasma concentration-effect relationships, which are often misleading when based on total drug concentration. It is also important when considering new dosage routes or formulations in order to optimize therapeutic plasma concentrations of the active enantiomer. Improvements in the sensitivity and selectivity of biological assays coupled with the developments in chiral analysis have made it possible to study the enantioselective disposition of drugs. Although valuable pharmacokinetic data were obtained for the beta 2-agonists by nonenantioselective methodology, more recent chiral studies have revealed the existence of extensive enantioselectivity in the disposition of these agents. The most significant features of the enantioselective disposition of albuterol are the relatively rapid plasma clearance and low bioavailability of the eutomer. Although this in itself does not necessarily justify the development of a single enantiomer formulation, the implications of the high levels of distomer after i.v. and oral dosing await clarification. Similarly, more work is required to elucidate the consequences of the major difference in disposition between albuterol and terbutaline in humans through both in vivo and in vitro studies of the mechanisms giving rise to this phenomenon. The enantioselective disposition of the other clinically used beta 2-agonists, such as fenoterol, formoterol, and salmeterol also needs to be characterized. The metabolism of the majority of beta 2-agonists is generally by conjugation to give one major metabolite. The situation is therefore uncomplicated by multiple metabolic pathways, which may differ in the extent and direction of their enantioselectivity. Many beta 2-agonists are excreted largely unchanged in the urine making studies of urinary excretion accessible without the requirement for very sensitive assays. The realization that the enantiomers of beta 2-agonists previously thought of as "inactive" may be associated with toxic effects is a further compelling reason to study the enantioselective pharmacokinetics of this class of drugs. In addition, the role of enantiomers in producing side effects, such as tremor and reduction in renal function, needs to be reassessed. The beta 2-agonists can be looked on as textbook examples of the inherent danger of ignoring chirality in the study of pharmacokinetics and pharmacodynamics. The growing body of information on the enantioselective disposition of beta 2-agonists in humans will enhance the rational use of these drugs in the future management of patients.

Formoterol. A review of its pharmacological properties and therapeutic potential in reversible obstructive airways disease

Formoterol, a long-acting beta 2-selective adrenoceptor agonist, produces dose-proportional bronchodilation in patients with obstructive airways disease with a reversible component. A significant effect occurs within minutes of inhalation of a therapeutic formoterol dose and persists for approximately 12 hours. Oral formoterol has a slower onset of action than the inhaled formulations, but also produces prolonged bronchodilatory effects. Inhaled formoterol has shown a therapeutic efficacy equivalent to or better than comparable dosages of the conventional beta 2-agonists salbutamol, fenoterol and terbutaline in short and long term trials, in both adults and children with asthma. Its prolonged duration of action permits a twice-daily dosage regimen and results in improved control of nocturnal symptoms by reducing the 'morning dip'. Formoterol also compares well with oral slow release theophylline. In addition, significantly more patients with chronic obstructive airways disease (COAD) had an improvement in symptoms when treated with formoterol compared with salbutamol or fenoterol. Noncomparative studies indicate formoterol also provides effective prophylaxis of exercise-induced asthma. Development of tachyphylaxis has not been observed. Formoterol is generally well tolerated. Adverse effects observed represent predictable extensions of its pharmacology. Tremor and palpitations are most frequently reported. The incidence of adverse events is dose-proportional and therefore related to the route of administration, being more frequent following oral than inhalation therapy. The long-acting beta 2-agonists, including formoterol, represent a significant advance over current maintenance or prophylactic bronchodilator therapy with intermediate-acting beta 2-agonists such as salbutamol, fenoterol and terbutaline, predominantly because of the twice daily administration regimen. However, comparisons with other long-acting beta 2-agonists, such as salmeterol, evaluation of its role in improving symptom control in patients failing to respond to prophylactic therapy, and clarification of the optimal role of beta 2-agonists in asthma maintenance therapy are required to fully determine the value of formoterol in the management of obstructive airways disease.