Arformoterol Tartrate : A Review of Pharmacology , Analysis and Clinical Studies

This article is a review of the therapeutic significance of arformoterol tartrate, a new generation β2 adrenergic agonist bronchodilator available in a nebulized form. Arformoterol is well absorbed through the lungs when administered via a standard jet nebulizer and is useful in long-term maintenance therapy of bronchoconstriction in chronic obstructive pulmonary disease (COPD). Much clinical evidence suggest the potentially enhanced efficacy of this drug in the treatment of COPD including chronic bronchitis and emphysema. Various hyphenated analytical methodologies have also been employed for the determination and quantification of arformoterol. This review provides an updated account on the pharmacology, pharmacokinetics, clinical studies, analytical techniques, drug-drug interactions, contraindications, and therapeutic applications of arformoterol tartrate.


INTRODUCTION
Global Initiative for Chronic Obstructive Lung Disease (GOLD) has defined chronic obstructive pulmonary disease (COPD) as a disease state characterized by airflow limitation that is not fully reversible.It is a progressive ailment generally associated with chronic reduced airflow, breathing difficulty, and pathologic pulmonary changes.It includes emphysema, an anatomically defined condition characterized by destruction and enlargement of the lung alveoli; chronic bronchitis which is a condition with chronic or recurrent excessive mucus secretion; and small airways disease, a condition in which small bronchioles are narrowed [1][2][3][4].The characteristic symptoms of COPD are chronic and progressive dyspnea, cough, and sputum production.Chronic cough and sputum production may precede the development of airflow limitation.COPD is also characterized by various pathologic changes in proximal airways, peripheral airways, lung parenchyma, and pulmonary vasculature [5].
Most of the information available on COPD prevalence, morbidity and mortality comes from developed countries [6].In 2000, over 119,000 deaths in the United States and 2.74 million deaths worldwide were attributed to COPD.Data from the National Health Interview Survey in 2001 indicates that 12.1 million people over age 25 years in the United States had COPD.Over 9 million of these individuals had chronic bronchitis; the others had emphysema or a combination of both diseases [4].A study conducted by the Global Burden of Disease under the auspices of the World Health Organization (WHO) and the World Bank concluded that the worldwide prevalence of COPD in 1990 was 9.34/1,000 and 7.33/1,000 in men and women, respectively.The prevalence of this disease is highest in those countries where cigarette smoking is very common [6].This disease accounted for 8 million medical outpatient visits, 1.5 million visits to emergency departments, and over 700,000 hospitalizations in the year 2000 [7].
COPD is the fourth leading cause of death in the United States, exceeded only by cancer, heart disease and cerebrovascular accidents, accounting for 120,816 deaths in 2002 [4,7].In the European Union, respiratory diseases accounted for a total direct cost of about 6 % of the total healthcare budget, with 56 % (€38.6 billion) of this expenditure due to COPD [5].The reported physician-diagnosed COPD prevalence is approximately 10 million people in United States but nearly 24 million persons may have COPD as indicated by self-reporting surveys.Compared to other common chronic diseases, the prevalence of COPD has steadily increased during the past 30 years and it is estimated that by the year 2020, it will become the third leading cause of death worldwide.In 2004, the economic impact of COPD was estimated at US$37.2 billion, including over US$16 billion in indirect morbidity and mortality costs [4,7].COPD was ranked sixth as the cause of death in 1990 by the study projected by Global Burden of Disease [5].
A variety of factors appear to increase the risk of developing COPD.These include asthma, air pollution, respiratory infections, chemicals, prenatal or childhood illness, nutrition and certain occupational dusts; of these, cigarette smoking remains the most important.Several investigation techniques for COPD includes the application of chest Xray, spirometry, helium dilution technique and computed tomography which allow the detection, characterization and diagnosis of this disease [8].Table 1 summarizes the various stages of COPD severity.
Inflammation of the airway wall is also associated with asthma.Increased number of various types of inflammatory cells, most notably eosinophils but also basophils, mast cells, macrophages, and certain types of lymphocytes, may be observed in airway walls [9].  1.The molecular weight of this drug is 494.5 g/mol.It is a white to off white solid powder, slightly soluble in water [11,12].Its pharmacological effects can be attributed to the increased intracellular cyclic adenosine monophosphate (cAMP) levels that result from the stimulation of intracellular adenyl cyclase.Increased intracellular cAMP level causes relaxation of bronchial smooth muscles and inhibits the release of mediators of immediate hypersensitivity from cells, especially mast cells [12].

Pharmacokinetics
Arformoterol tartrate is well absorbed through lungs when administered by a nebulizer.The mean peak plasma concentration (C max ) and systemic exposure (AUC 0-12h ) are 4.3 pg/mL and 34.5 pg.h/mL, respectively, when 15 µg arformoterol is administered every 12 h for 14 days in COPD patients.The time to achieve median steady state peak plasma concentration (t max ) is approximately half an hour after drug administration.The mean terminal half-life is 26 h in COPD patients when treated with 15 µg inhaled arformoterol twice daily for 14 days.The binding of arformoterol to human plasma proteins in vitro is 52-65% at concentrations of 0.25, 0.5 and 1.0 ng/mL of radiolabeled arformoterol.Metabolism occurs primarily by direct conjugation (glucuronidation) and secondary route of metabolism is via O-demethylation.Metabolism is mediated by atleast five human uridine diphosphoglucuronosyltransferase (UGT) isozymes as well as CYP2D6 and CYP2C19.After administration of a single oral dose of radiolabeled arformoterol, 63% of the radioactive amount was recovered in urine and 11% in feces within 48 h.A total of 89% of the total radioactive dose was recovered within 14 days, with 67% in urine and 22% in faeces [11].

Clinical studies
Several clinical studies have been conducted with arformoterol tartrate to determine its pharmacokinetics and/or pharmacodynamics efficacy.Baumgartner et al conducted clinical trials on 717 patients with COPD using arformoterol tartrate and salmeterol xinafoate versus placebo in a 12-week, multicenter, double-blind, double-dummy and randomized study.All patients, including male and female (aged ≥ 35 years), with physician-diagnosed COPD received arformoterol (15 µg bid, 25 µg bid, or 50 µg qid via nebulizer), salmeterol (42 µg bid via metered-dose inhaler, MDI), or placebo.In the study, patients with moderate to severe COPD treated with nebulized arformoterol were observed to have significant and sustained improvement in airways functions and dyspnea compared to placebo [13].
Tashkin et al conducted a clinical study which was designed to evaluate the safety and efficacy of concomitant treatment with nebulized arformoterol 15 µg bid and tiotropium 18 µg qid dry powder inhaler (DPI) in the treatment of COPD.It was a 2-week, prospective, multicenter, randomized, modified-blind, and double dummy, parallel group study.The results demonstrated mean FEV 1 AUC 0-24h improvement from baseline for arformoterol (0.10 L) and tiotropium (0.08 L) treatment groups and greater for the combined therapy (0.22 L).Peak FEV 1 , peak FVC and dyspnea were also improved in mono-therapies and greatest with combined therapy [14] Hanrahan et al also performed a doubleblind, 12-week, randomized trial to determine the effect of nebulized arformoterol on airway function in patients with COPD.Pulmonary function efficacy of nebulized arformoterol (15 µg bid, 25 µg bid, 50 µg qid) and salmeterol MDI (42 µg bid) versus placebo was assessed in 1456 subjects.The percent change in trough FEV 1 , percent change in FEV 1 average AUC 0-12h and peak percent change in FEV 1 from pre-dose were analyzed.The results demonstrated that improvement in trough FEV 1 over 12 weeks was greater for arformoterol and salmeterol versus placebo.Increase in FEV 1 AUC 0-12h and peak percent change was also greater for arformoterol than for salmeterol.After 12 weeks study, 78-87 % of arformoterol subjects had ≥ 10 % increase in FEV 1 from pre-dose (56% salmeterol, 44 % placebo).Trials demonstrated a significant and sustained improvement in lung function over 12 weeks with COPD subjects on nebulized arformoterol [17].In the same year, the authors also undertook two double-blind, randomized clinical trials to describe the pretreatment arrhythmia occurrence frequency in patients with COPD and to determine the effects of inhaled long-acting β 2 -agonists such as arformoterol and salmeterol.
In this study, 24 h Holter monitoring data were pooled from two identically designed phase III trials.The patients were randomized to LABA treatment or placebo for

Analytical techniques, pharmacokinetics and compatibility
(R, R)-formoterol and (S, S)-formoterol in human plasma have been analyzed using a sensitive and robust LC-MS-MS method with an Astec chirobiotic T2 column (250 x 2.0 mm).The mobile phase consisted of methanol/acetonitrile/H 2 O containing 10 mM NH 4 COOH: 78/20/2 (v/v/v) with 0.25 and 0.006% CH 3 COOH and NH 4 OH, respectively.The flow rate was 0.2 mL/min and injection volume 30 µL.The results showed that there was no matrix interference across the elution windows of (R,R)-formoterol and (S,S)formoterol.The mean (n = 3) correlation coefficients in human plasma were 0.9994 ± 0.0002 and 0.9985 ± 0.0005 for (R, R)formoterol and (S, S)-formoterol, respectively.Thus, a validated method has been successfully employed for the quantification of both isomers of formoterol in human plasma.No inversion of (R,R)-formoterol to (S,S)-formoterol was observed [20].
The pharmacokinetics of arformoterol tartrate inhalation solution in subjects classified as poor versus extensive Cytochrome P450 (CYP) 2D6 metabolizers or with reduced uridine diphosphate glycosyltransferase 1 polypeptide A1 (UGT1A1) activity has been characterized.
Plasma samples were collected up to 168 h post-dose and were analyzed by a validated chiral LC/MS/MS method.The results indicated that subjects with reduced CYP2D6 and/or UGT1A1 enzyme activity did not exhibit any increase in systemic exposure to (R,R)-formoterol compared with subjects with normal CYP2D6 and/or UGT1A1 enzyme activity [21].
Chemical and physical compatibility of arformoterol (15 µg/2mL) with ipratropium bromide (0.5 mg/2.5mL),acetylcysteine (800 mg/4mL), and budesonide (0.25 mg/2mL and 0.5 mg/2mL) was assessed using visual inspection, pH measurement and HPLC assay of each active component.The findings indicate that there was no visible signs of change and the pH of all admixtures ranged from 4.82 to 6.40, which was within the range of individual drugs.The content of each active component in all the admixtures ranged from 98.3 to 101.4 %, compared to the control thus indicating that the acceptance criteria of not more than 10.0 % were met [22].
In another study, human hepatoma cells were cultured in the presence of (R,R)-formoterol and Na 2 35 SO 4 to determine whether formoterol is metabolized by sulphate conjugation.The accumulated radiolabeled sulphate conjugates were determined by reversed phase HPLC and scintillation counting of peaks.Mass spectroscopy analysis of individual peaks allowed identification of the fragments of formoterol sulphate.Separation of the constituents of culture medium by reversed phase HPLC produced a major peak with a retention time of 12 min [10].
The levels of (R,R)-formoterol and (S,S)formoterol have also been measured using a validated chiral analytical method, in accordance with the United States Food and Drug Administration (USFDA) guidelines.Pharmacokinetic parameters for (R,R)-and (S,S)-formoterol were also determined by non-compartmental methods using WinNonlin Professional 5.1.1 (Pharsight, Mountainview, CA).The results indicate that in vivo chiral inversion did not occur during treatment with arformoterol [16].In yet another work, a validated chiral HPLC method was successfully applied for the determination of formoterol stereoisomers and their inversion products in an aqueous matrix stored at 5 -70 0 C up to 3 weeks.Analysis was performed on a chiral-AGP column (100 x 4 mm, 5 µm) using a variable mixture of mobile phase at a flow rate of 1.3 mL/min and UV detection at 242 nm.All four formoterol stereoisomers were adequately resolved with acceptable detection.The method showed acceptable accuracy (> 88 %), precision (RSD < 8.5 %) and good linearity (r 2 > 0.9999) over the concentration range investigated.No significant difference in inversion of the active components in racemic (R, R/S, S)-formoterol fumarate and the single isomer (R, R)arformoterol tartrate drug formulations was observed [23].
Thus, the foregoing indicate that a number of advanced analytical techniques such as chiral HPLC, LC-MS-MS, reversed phase HPLC, etc, can be suitably employed for the quantification of arformoterol tartrate.These methods have not only facilitated the biochemical analysis of the compound but also the determination of its pharmacokinetic and pharmacodynamic parameters, etc.

Dosage
The recommended dose of arformoterol for patients with COPD is 15 µg administered twice daily (morning and evening) by nebulization.It should be administered via a standard jet nebulizer connected to an air compressor.The solution requires no dilution prior to administration [11,12].However, investigational studies also emphasize that the choice of nebulizer/compressor system can influence the aerosol properties of arformoterol inhalation solution and should be considered when prescribing nebulized medications [24].

Adverse effects
The adverse effects of arformoterol in patients have been attributed to its activity at β 2 adrenergic receptors, similar to those of other β 2 -agonists.Table 2 summarizes the adverse events reported in at least 2 % of patients for arformoterol compared with placebo in clinical trials.These include arrhythmias, atrial tachycardia, pain, chest pain, diarrhea, back pain, sinusitis, rashes, leg cramps and dyspneoa.Some clinical trials also reported other adverse effects such as tremors, insomnia and nervousness [11].However, the safety profile of arformoterol has been recently documented [25,26].

Fig. 1 :
Fig. 1: Structure of arformoterol tartrate Pharmacology Arformoterol is a potent, selective, β 2 adrenergic agonist and long acting bronchodilator which acts in a way similar to that of other β 2 adrenergic agonists such as formoterol and salmeterol.Its pharmacological effects can be attributed to the increased intracellular cyclic adenosine monophosphate (cAMP) levels that result from the stimulation of intracellular adenyl cyclase.Increased intracellular cAMP level causes relaxation of bronchial smooth muscles and inhibits the release of mediators of immediate hypersensitivity from cells, especially mast cells[12].

Table 1 :
[1,2]us stages of COPD severity[1,2] . It was an open-label, two-week randomized, multicenter, multi-dose, threeway crossover study conducted on 39 subjects who received study medication twice daily, among whom 33 subjects (84.6 %) received all treatments and completed the trial.In this study, steady-state exposure to (R, R)-formoterol in COPD subjects was similar following 14 days of administration of either 15 µg nebulized arformoterol or 12 µg of racemic formoterol DPI and lower than that with 24 µg racemic formoterol DPI[16].