Safety of long-acting beta2-agonists in the treatment of asthma

Pharmacology and Therapeutics of Bronchodilators Revisited

Bronchodilators remain the cornerstone of the treatment of airway disorders such as asthma and chronic obstructive pulmonary disease (COPD). There is therefore considerable interest in understanding how to optimize the use of our existing classes of bronchodilator and in identifying novel classes of bronchodilator drugs. However, new classes of bronchodilator have proved challenging to develop because many of these have no better efficacy than existing classes of bronchodilator and often have unacceptable safety profiles. Recent research has shown that optimization of bronchodilation occurs when both arms of the autonomic nervous system are affected through antagonism of muscarinic receptors to reduce the influence of parasympathetic innervation of the lung and through stimulation of β ₂-adrenoceptors (β ₂-ARs) on airway smooth muscle with β ₂-AR-selective agonists to mimic the sympathetic influence on the lung. This is currently achieved by use of fixed-dose combinations of inhaled long-acting β ₂-adrenoceptor agonists (LABAs) and long-acting muscarinic acetylcholine receptor antagonists (LAMAs). Due to the distinct mechanisms of action of LAMAs and LABAs, the additive/synergistic effects of using these drug classes together has been extensively investigated. More recently, so-called "triple inhalers" containing fixed-dose combinations of both classes of bronchodilator (dual bronchodilation) and an inhaled corticosteroid in the same inhaler have been developed. Furthermore, a number of so-called "bifunctional drugs" having two different primary pharmacological actions in the same molecule are under development. This review discusses recent advancements in knowledge on bronchodilators and bifunctional drugs for the treatment of asthma and COPD. SIGNIFICANCE STATEMENT: Since our last review in 2012, there has been considerable research to identify novel classes of bronchodilator drugs, to further understand how to optimize the use of the existing classes of bronchodilator, and to better understand the role of bifunctional drugs in the treatment of asthma and chronic obstructive pulmonary disease.

Ultra-LABAs for the treatment of asthma

The term ultra-LABA indicates once-daily β2-AR agonists (abediterol, indacaterol, olodaterol and vilanterol) that are single enantiomers of the (R)-configuration. All have a near full-agonist profile at human β2-AR. They can be prescribed in asthmatics only when associated with an with ICS, although further confirmations need to clarify what really these agents add if used in association to ICS and in what asthmatic patients this association may have more value. They are also under development in triple inhalers that include an ultra-LABA, a LAMA and an ICS. The once-daily posology might increase adherence in long-term treatment of asthma but superiority to twice-daily LABAs has not yet been fully demonstrated. In any case, still no ultra-LABA can be recommended as preferred.

Salmeterol with Liver Depot Gene Therapy Enhances the Skeletal Muscle Response in Murine Pompe Disease

Gene therapy for Pompe disease with adeno-associated virus (AAV) vectors has advanced into early phase clinical trials; however, the paucity of cation-independent mannose-6-phosphate receptor (CI-MPR) in skeletal muscle, where it is needed to take up acid α-glucosidase (GAA), has impeded the efficacy of Pompe disease gene therapy. Long-acting selective β2 receptor agonists previously enhanced the CI-MPR expression in muscle. In this study we have evaluated the selective β2 agonist salmeterol in GAA knockout mice in combination with an AAV vector expressing human GAA specifically in the liver. Quadriceps glycogen content was significantly decreased by administration of the AAV vector with salmeterol, in comparison with the AAV vector alone (p < 0.01). Importantly, glycogen content of the quadriceps was reduced to its lowest level by the combination of AAV vector and salmeterol administration. Rotarod testing revealed significant improvement following treatment, in comparison with untreated mice, and salmeterol improved wirehang performance. Salmeterol treatment decreased abnormalities of autophagy in the quadriceps, as shown be lower LC3 and p62. Vector administration reduced the abnormal vacuolization and accumulation of nuclei in skeletal muscle. Thus, salmeterol could be further developed as adjunctive therapy to improve the efficacy of liver depot gene therapy for Pompe disease.

Air pollution and resistance to inhaled glucocorticoids: Evidence, mechanisms and gaps to fill

Substantial evidence indicates that cigarette smoke exposure induces resistance to glucocorticoids, the primary maintenance medication in asthma treatment. Modest evidence also suggests that air pollution may reduce the effectiveness of these critical medications. Cigarette smoke, which has clear parallels with air pollution, has been shown to induce glucocorticoid resistance in asthma and it has been speculated that air pollution may have similar effects. However, the literature on an association of air pollution with glucocorticoid resistance is modest to date. In this review, we detail the evidence for, and against, the effects of air pollution on glucocorticoid effectiveness, focusing on results from epidemiology and controlled human exposure studies. Epidemiological studies indicate a correlation between increased air pollution exposure and worse asthma symptoms. But these studies also show a mix of beneficial and harmful effects of glucocorticoids on spirometry and asthma symptoms, perhaps due to confounding influences, or the induction of glucocorticoid resistance. We describe mechanisms that may contribute to reductions in glucocorticoid responsiveness following air pollution exposure, including changes to phosphorylation or oxidation of the glucocorticoid receptor, repression by cytokines, or inflammatory pathways, and epigenetic effects. Possible interactions between air pollution and respiratory infections are also briefly discussed. Finally, we detail a number of therapies that may boost glucocorticoid effectiveness or reverse resistance in the presence of air pollution, and comment on the beneficial effects of engineering controls, such as air filtration and asthma action plans. We also call attention to the benefits of improved clean air policy on asthma. This review highlights numerous gaps in our knowledge of the interactions between air pollution and glucocorticoids to encourage further research in this area with a view to reducing the harm caused to those with airways disease.

Protection against severe hypokalemia but impaired cardiac repolarization after intense rowing exercise in healthy humans receiving salbutamol

Intense exercise induces pronounced hyperkalemia, followed by transient hypokalemia in recovery. We investigated whether the β₂ agonist salbutamol attenuated the exercise hyperkalemia and exacerbated the postexercise hypokalemia, and whether hypokalemia was associated with impaired cardiac repolarization (QT hysteresis). Eleven healthy adults participated in a randomized, counterbalanced, double-blind trial receiving either 1,000 µg salbutamol (SAL) or placebo (PLAC) by inhalation. Arterial plasma potassium concentration ([K⁺]_a) was measured at rest, during 3 min of intense rowing exercise, and during 60 min of recovery. QT hysteresis was calculated from ECG ( n = 8). [K⁺]_a increased above baseline during exercise (rest, 3.72 ± 0.7 vs. end-exercise, 6.81 ± 1.4 mM, P < 0.001, mean ± SD) and decreased rapidly during early recovery to below baseline; restoration was incomplete at 60 min postexercise ( P < 0.05). [K⁺]_a was less during SAL than PLAC (4.39 ± 0.13 vs. 4.73 ± 0.19 mM, pooled across all times, P = 0.001, treatment main effect). [K⁺]_a was lower after SAL than PLAC, from 2 min preexercise until 2.5 min during exercise, and at 50 and 60 min postexercise ( P < 0.05). The postexercise decline in [K⁺]_a was correlated with QT hysteresis ( r = 0.343, n = 112, pooled data, P = 0.001). Therefore, the decrease in [K⁺]_a from end-exercise by ~4 mM was associated with reduced QT hysteresis by ~75 ms. Although salbutamol lowered [K⁺]_a during exercise, no additive hypokalemic effects occurred in early recovery, suggesting there may be a protective mechanism against severe or prolonged hypokalemia after exercise when treated by salbutamol. This is important because postexercise hypokalemia impaired cardiac repolarization, which could potentially trigger arrhythmias and sudden cardiac death in susceptible individuals with preexisting hypokalemia and/or heart disease. NEW & NOTEWORTHY Intense rowing exercise induced a marked increase in arterial potassium, followed by a pronounced decline to hypokalemic levels. The β₂ agonist salbutamol lowered potassium during exercise and late recovery but not during early postexercise, suggesting a protective effect against severe hypokalemia. The decreased potassium in recovery was associated with impaired cardiac QT hysteresis, suggesting a link between postexercise potassium and the heart, with implications for increased risk of cardiac arrhythmias and, potentially, sudden cardiac death.

The effect of tiotropium in combination with olodaterol on house dust mite-induced allergic airway disease

One of the major goals of asthma therapy is to maintain asthma control and prevent acute exacerbations. Long-acting bronchodilators are regularly used for the treatment of asthma patients and in clinical studies the anti-cholinergic tiotropium has recently been shown to reduce exacerbations in patients with asthma. So far it is unclear how tiotropium exerts this effect. For this purpose, we designed an allergen-driven rechallenge model of allergic airway inflammation in mice, to assess the effectiveness of tiotropium and the long-acting β-2 adrenoceptor agonist olodaterol on allergen-induced exacerbations of airway disease. Female C57BL/6J mice were sensitized intranasally (i.n.) with 1 μg of house dust mite (HDM) extract followed by a challenge regime (5 consecutive days 10 μg HDM extract i.n.) after one week. Mice were exposed to a secondary challenge five weeks after sensitization and were treated i.n. with different concentrations of tiotropium or olodaterol (1, 10 and 100 μg/kg) or a combination thereof (10 μg/kg each) prior to and during the secondary challenge period. Three days after the last challenge, bronchoalveolar lavage (BAL) fluid and lung tissue were collected for flow cytometry and histologic analysis, respectively. Secondary challenge with HDM extract strongly induced allergic airway disease reflected by inflammatory cell infiltration and goblet cell metaplasia. Treatment with tiotropium, but not with olodaterol reduced tissue inflammation and goblet cell metaplasia in a dose-dependent manner. The combination of tiotropium and olodaterol was more effective in significantly reducing tissue inflammation compared to tiotropium treatment alone, and also led to a decrease in BAL cell counts. These data suggest that in a model of relapsing allergic airway disease tiotropium directly prevents exacerbations by reducing inflammation and mucus production in the airways. In addition, the combination of tiotropium and olodaterol exerts synergistic effects.

Efficacy and Safety of Roflumilast in Korean Patients with COPD

PURPOSE

Roflumilast is the only oral phosphodiesterase 4 inhibitor approved to treat chronic obstructive pulmonary disease (COPD) patients [post-bronchodilator forced expiratory volume in 1 second (FEV₁) <50% predicted] with chronic bronchitis and a history of frequent exacerbations. This study evaluated the efficacy and safety of roflumilast in Korean patients with COPD and compared the efficacy based on the severity of airflow limitation.

MATERIALS AND METHODS

A post-hoc subgroup analysis was performed in Korean COPD patients participating in JADE, a 12-week, double-blinded, placebo-controlled, parallel-group, phase III trial in Asia. The primary efficacy endpoint was the mean [least-squares mean adjusted for covariates (LSMean)] change in post-bronchodilator FEV₁ from baseline to each post-randomization visit. Safety endpoints included adverse events (AEs) and changes in laboratory values, vital signs, and electrocardiograms.

RESULTS

A total of 260 Korean COPD patients were recruited, of which 207 were randomized to roflumilast (n=102) or placebo (n=105) treatment. After 12 weeks, LSMean post-bronchodilator FEV₁ increased by 43 mL for patients receiving roflumilast and decreased by 60 mL for those taking placebo. Adverse events were more common in the roflumilast group than in the placebo group; however, the types and frequency of AEs were comparable to those reported in previous studies.

CONCLUSION

Roflumilast significantly improved lung function with a tolerable safety profile in Korean COPD patients irrespective of the severity of airflow limitation.

The Lipid-lowering Effects of R-bambuterol in Healthy Chinese Volunteers: A Randomized Phase I Clinical Study

Background

Existing treatments are inadequate for patients at high risk of coronary heart disease caused by elevated levels of plasma low-density lipoprotein cholesterol (LDL-C). Bambuterol is a prodrug of β2-agonist commonly used for the treatment of asthma and chronic obstructive pulmonary disease (COPD) with the advantage of once daily dosing and favorable side effect profile. The potential lipid-lowering effects of bambuterol were unclear, possibly due to the racemic bambuterol (rac-bambuterol) that was used in previous studies.

Methods

The lipid-lowering effects of R-bambuterol were examined in a randomized phase I trial in 48 healthy Chinese volunteers aged 18–45 years. Participants were randomly assigned to five groups to receive a single dose (2.5 mg, 5 mg or 10 mg) or multiple doses (5 mg) of oral medications of R-bambuterol, or a single dose of rac-bambuterol (10 mg). Plasma lipid levels were measured at baseline, time to peak concentration (T_max) and 24 h after the treatment.

Findings

Administration of a single-dose of R-bambuterol resulted in dose-dependent reductions in the levels of plasma LDL-C, high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC), apolipoprotein B (ApoB) and apolipoprotein A1 (ApoA1) at T_max. Levels of LDL-C exhibited the most reductions, which were statistically significant in all three single-dose R-bambuterol groups (all P values < 0.05). R-bambuterol was more potent in LDL-C lowering compared to rac-bambuterol at T_max (P = 0.08). At 24 h after dosing, the significant lipid lowering effects of R-bambuterol sustained for LDL-C (P = 0.01), ApoB (P = 0.001) and ApoA1 (P = 0.03), but not for HDL-C. The ratio of ApoA1/ApoB was marginally increased (P = 0.06). In the multiple-dose group, LDL-C levels again were significantly reduced (all P values < 0.05), whereas the ratios of ApoA1/ApoB were marginally increased.

Interpretation

R-bambuterol can lower the plasma levels of LDL-C, and marginally raise the ratio of ApoA1/ApoB (indicator of HDL-C/LDL-C) with both a single dose and multiple doses. R-bambuterol was more potent in LDL-C lowering than rac-bambuterol.

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Oral administration of R-bambuterol, a long-acting bronchodilator, can significantly lower LDL cholesterol in healthy Chinese volunteers.

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R-bambuterol was more potent than rac-bambuterol in lowering LDL-C and raising the ratio of ApoA1/ApoB.

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It may provide an alternative for treating high cholesterol, especially for those also suffering from COPD.

The anti-asthma herbal medicine ASHMI acutely inhibits airway smooth muscle contraction via prostaglandin E2 activation of EP2/EP4 receptors

Our previous studies have shown that the anti-asthma traditional Chinese medicine herbal formula ASHMI (anti-asthma simplified herbal medicine intervention) inhibits acetylcholine-induced contractions of tracheal rings from ovalbumin-sensitized and naive mice in a β-adrenoceptor-independent manner. We sought to determine whether acute in vivo ASHMI administration inhibits airway hyperreactivity (AHR) in a murine model of allergic asthma and acetylcholine-induced tracheal ring constriction ex vivo and to elucidate the cellular mechanisms underlying these effects. Ovalbumin-sensitized mice received a single oral ASHMI dose 2 h before intravenous acetylcholine challenge. AHR was determined by invasive airway measurements. Myography was used to determine the effects of ASHMI on acetylcholine-induced constriction of tracheal rings from asthmatic mice with or without epithelial denudation. The effect of cyclooxygenase inhibition and EP2/EP4 receptor blockade on ASHMI attenuation of acetylcholine contractions was evaluated. Tracheal cAMP and PGE2 levels were measured by ELISA. A single acute oral dose of ASHMI dramatically reduced AHR in response to acetylcholine provocation in ovalbumin-sensitized mice (P < 0.001). In ex vivo experiments, ASHMI significantly and dose-dependently reduced tracheal ring constriction to acetylcholine (P < 0.05-0.001), which was epithelium independent and associated with elevated cAMP levels. This effect was abrogated by cyclooxygenase inhibition or EP2/EP4 receptor blockade. ASHMI also inhibited contraction to high K(+) (P < 0.001). ASHMI increased tracheal ring PGE2 release in response to acetylcholine or high K(+) (P < 0.05 for both). ASHMI produced direct and acute inhibition of AHR in vivo and blocked acetylcholine-induced tracheal ring constriction via the EP2/EP4 receptor pathway, identifying the mechanism by which ASHMI is an orally active bronchoprotective agent.

In vitro effects of Beta-2 agonists on skeletal muscle differentiation, hypertrophy, and atrophy

Background

Beta-2 agonists are widely used in the treatment of asthma and chronic obstructive pulmonary disease for their effect on airway smooth muscle relaxation. They also act on skeletal muscle, although their reported ergogenic effect is controversial.

Aim

To evaluate the in vitro effects of short-acting and long-acting beta-2 agonists on adrenergic receptor (ADR) expression, hypertrophy, and atrophy markers, in a skeletal muscle cell line.

Methods

The C2C12 cell line was used as a model of skeletal muscle differentiation. ADR messenger RNA expression was evaluated in proliferating myoblasts, committed cells, and differentiated myotubes, in basal conditions and after treatment with 10^-6 M clenbuterol, salbutamol, salmeterol, and formoterol. Effect of beta-2 agonists on gene and protein expression of hypertrophy and atrophy markers was assessed in differentiated myotubes.

Results

Our study shows that beta-2 ADR messenger RNA was expressed and progressively increased during cell differentiation. Beta-2 agonist treatment did not affect its expression. Skeletal muscle hypertrophy markers (fast and slow myosin, myogenin) were not modulated by any of the beta-2 agonists evaluated. However, clenbuterol induced a significant, dose-dependent downregulation of skeletal muscle atrophy genes (atrogin-1, MuRF-1, and cathepsin L).

Conclusions

The reported ergogenic effect of beta-2 agonists, if any, should be considered as drug-specific and not class-specific and that of clenbuterol is mediated by the inhibition of the atrophic pathway.

Pharmacotherapy for exercise-induced asthma: allowing normal levels of activity and sport

Exercise-induced bronchoconstriction (EIB) is experienced by the majority of an estimated 300 million individuals who have asthma, a condition that affects all ages and is increasing globally. Respiratory water loss with dehydration of the airways causing mediator release and airway narrowing is considered the cause of EIB, the severity of which will be increased if the inhaled air is cold or polluted. Adequate control of asthma is essential to minimize or prevent EIB and permit normal levels of physical activity and sport. This is important because exercise is a necessary component of daily living, assists in obtaining and maintaining a healthy body and has been demonstrated to benefit asthmatics. Inhaled glucocorticosteroids and inhaled β(2)-adrenoceptor agonists (IβA) are the pharmacological agents of choice to manage asthma and minimize EIB, assisted when necessary, by other drugs including leukotriene receptor antagonists and chromones. Tolerance from daily use of IβA is of concern and more flexible drug therapy needs to be considered. Optimal use of inhalers to deliver drugs effectively requires closer attention. Pharmacogenetics may hold the key to future drug therapy.

Pharmacology and therapeutics of bronchodilators

Bronchodilators are central in the treatment of of airways disorders. They are the mainstay of the current management of chronic obstructive pulmonary disease (COPD) and are critical in the symptomatic management of asthma, although controversies around the use of these drugs remain. Bronchodilators work through their direct relaxation effect on airway smooth muscle cells. at present, three major classes of bronchodilators, β(2)-adrenoceptor (AR) agonists, muscarinic receptor antagonists, and xanthines are available and can be used individually or in combination. The use of the inhaled route is currently preferred to minimize systemic effects. Fast- and short-acting agents are best used for rescue of symptoms, whereas long-acting agents are best used for maintenance therapy. It has proven difficult to discover novel classes of bronchodilator drugs, although potential new targets are emerging. Consequently, the logical approach has been to improve the existing bronchodilators, although several novel broncholytic classes are under development. An important step in simplifying asthma and COPD management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence. Several once-daily β(2)-AR agonists or ultra-long-acting β(2)-AR-agonists (LABAs), such as indacaterol, olodaterol, and vilanterol, are already in the market or under development for the treatment of COPD and asthma, but current recommendations suggest the use of LABAs only in combination with an inhaled corticosteroid. In addition, some new potentially long-acting antimuscarinic agents, such as glycopyrronium bromide (NVA-237), aclidinium bromide, and umeclidinium bromide (GSK573719), are under development, as well as combinations of several classes of long-acting bronchodilator drugs, in an attempt to simplify treatment regimens as much as possible. This review will describe the pharmacology and therapeutics of old, new, and emerging classes of bronchodilator.

Efficacy of tiotropium in COPD patients from Asia: a subgroup analysis from the UPLIFT trial

BACKGROUND AND OBJECTIVE

Studies in respiratory diseases other than chronic obstructive pulmonary disease suggest potentially differing responses to medications among patients from different regions. We report a subgroup analysis of patients recruited to Asian centres from a previously reported 4-year COPD trial.

METHODS

Subgroup analysis from a randomized, double-blinded, placebo-controlled trial of tiotropium 18 µg daily in COPD. Primary end-point was rate of decline in FEV(1) . Secondary end-points included spirometry at individual time points, health-related quality of life (St George's Respiratory Questionnaire), exacerbations and mortality.

RESULTS

Of 5992 patients, 362 were from Asian centres (100 from Japan). Mean age 66 years, 95% men, 13% current smokers, BMI: 21 kg/m(2) ; post-bronchodilator FEV(1) : 44% predicted; St George's Respiratory Questionnaire total score: 44 units. No treatment effect was observed for rate of decline in FEV(1) although annual decline was less in Asian patients. Morning pre-bronchodilator FEV(1) and forced vital capacity improved in Asian patients (P < 0.05). Tiotropium reduced number of exacerbations (rate ratio (95% confidence interval (CI)): 0.73 (0.57-0.94)). Hazard ratios (95%CI) for exacerbations and hospitalized exacerbations (tiotropium/control) were 0.81 (0.62-1.05) and 0.85 (0.61-1.19), respectively. St George's Respiratory Questionnaire total score improved by 1.5-6.1 units (P < 0.05 for months 18, 24, 30 and 36) with tiotropium. Fatal events occurred in 34 tiotropium (18.5%) and 42 control (23.6%) patients.

CONCLUSIONS

In COPD patients from Asia, tiotropium improves lung function, improves health-related quality of life and reduces exacerbations over 4 years of treatment.

Salmeterol or doxycycline do not inhibit acute bronchospasm and airway inflammation in cats with experimentally-induced asthma

The objective of this study was to determine if inhaled salmeterol, a long-acting β(2)-adrenergic agonist, and oral doxycycline, a tetracycline antibiotic displaying matrix metalloproteinase (MMP) inhibitory activity, reduce airway inflammation and obstruction in cats with experimentally-induced asthma. Eight Ascaris suum (AS)-sensitised cats were enrolled in a prospective study in which they underwent four AS-challenges at 1 month intervals. The challenged animals were given no treatment or were treated on 4 consecutive days with either: (1) oral prednisolone (1mg/kg twice daily), (2) inhaled salmeterol (50 μg twice daily), or (3) oral doxycycline (5mg/kg twice daily), according to a randomised cross-over design. Inhibition of allergen-induced early (EAR) and late (LAR) asthmatic reactions were assessed by barometric whole-body plethysmography. Cytology and measurement of MMP-2 and -9 activities were carried out on bronchoalveolar lavage fluid (BALF). Although none of the treatments prevented the EAR, prednisolone treatment inhibited the LAR. Relative to untreated cats, the eosinophil percentage and MMP-2 activity in BALF were significantly reduced following prednisolone treatment (P<0.05). Short-term therapy with either salmeterol or doxycycline had no effect on the EAR or LAR or on airway inflammation. Given the chronic nature of this disease in cats, long-term therapy may be required to produce more favourable functional and clinical outcomes.

β(2) -adrenoceptor agonists: current and future direction

Despite the passionate debate over the use of β(2) -adrenoceptor agonists in the treatment of airway disorders, these agents are still central in the symptomatic management of asthma and COPD. A variety of β(2) -adrenoceptor agonists with long half-lives, also called ultra long-acting β(2) -adrenoceptor agonists (ultra-LABAs; indacaterol, olodaterol, vilanterol, carmoterol, LAS100977 and PF-610355) are currently under development with the hopes of achieving once-daily dosing. It is likely that the once-daily dosing of a bronchodilator would be a significant convenience and probably a compliance-enhancing advantage, leading to improved overall clinical outcomes. As combination therapy with an inhaled corticosteroid (ICS) and a LABA is important for treating patients suffering from asthma, and a combination with an inhaled long-acting antimuscarinic agent (LAMA) is important for treating COPD patients whose conditions are not sufficiently controlled by monotherapy with a β(2) -adrenoceptor agonist, some novel once-daily combinations of LABAs and ICSs or LAMAs are under development.

Evaluation of the effects of the R- and S-enantiomers of salbutamol on equine isolated bronchi

BACKGROUND

Equine obstructive pulmonary disease, also known as heaves or recurrent airway obstruction (RAO) is a common equine pulmonary disease with some similarities to human asthma and COPD, which represents a major cause of morbidity and loss of lung performance. Salbutamol has been widely used for the treatment of human airway diseases and has usually been prepared as the racemic form of the drug. However, recently the R-enantiomer of salbutamol has been introduced into clinical practice in the treatment of asthma in humans and this has been suggested to be an improvement on the racemic form of the drug; therefore thus the S-enantiomer has been demonstrated to have adverse effects in the lung and thus using the R-enantiomer may improve the therapeutic ratio. However, little is known about the properties of the R- and S-enantiomers of salbutamol in equine airways and the present study has evaluated the relaxant effects of racemic β(2)-agonists in comparison with the R- and S-enantiomers in isolated equine isolated bronchi, as well as the bronchoprotective effects of these drugs on cholinergic and histaminergic pathway.

METHODS

We have studied the effects of the R- and S-enantiomers of salbutamol on bronchi isolated from RAO-affected or unaffected horses. The first study assayed the relaxant effects of R- and S-salbutamol on isolated bronchial rings contracted with carbachol or histamine at a sub-maximal concentration (EC70). A second study evaluated the effects of R- and S-salbutamol on semi-logarithmic cumulative concentration-response curves induced by carbachol or histamine. Specific software was used to calculate statistical significance and the appropriate sigmoidal curve-fitting model.

RESULTS

Neither enantiomers of salbutamol caused a relaxant effect on the sub-maximal plateau contractile effects of carbachol; in fact, both R- and S-salbutamol induced a slight, but significant contraction (P ≤ 0.05) compared to the controls. In contrast, R-salbutamol induced a significant relaxation of bronchi pre-contracted with histamine (RAO-unaffected: 92.06% ± 2.00; RAO-affected 100.20 ± 3.99; P ≤ 0.01). S-salbutamol induced a weak relaxation (RAO-unaffected: 15.81% ± 5.65; RAO-affected 12.36 ± 5.15) when compared to that induced by papaverine. The incubation with either R- or S-salbutamol shifted rightward (P ≤ 0.001) the carbachol contraction curve in RAO-unaffected bronchi, but not in RAO-affected bronchi, compared to control tissues. R-salbutamol induced a reduction in E(max) values (C: 9.07 gr ± 0.68; R-salb.: 6.36 gr ± 0.21; P ≤ 0.01) in normal bronchi. On the contrary it reduced the histamine potency in RAO-affected bronchi (EC50 7.10 μM ± 0.35, P < 0.001). The incubation with S-salbutamol shifted leftward the histamine concentration curve in both normal bronchi (C: 7.00 μM ± 0.29; S-salb.: 2.25 μM ± 0.19; P ≤ 0.001) and bronchi from RAO-affected horses (C: 2.80 μM ± 0.26; S-salb.: 1.50 μM ± 0.80; P ≤ 0.05).

CONCLUSION

Our studies have demonstrated that S-salbutamol elicited a modest increase in contraction of equine airway smooth muscle induced by carbachol and induced a significant hyperresponsiveness to histamine. These results confirm the ability of the S-enantiomer of salbutamol to potentiate the contractile effect of certain spasmogens on airway smooth muscle. Such an adverse effect would be determined in the airways of horses with RAO and suggest that if salbutamol is to be used in the treatment of symptoms of RAO in horses, the R-enantiomer, rather than the racemic mixture should be considered.

Use and safety of long-acting β2-agonists for pediatric asthma

Asthma guidelines recommend the use of long-acting β2-agonists (LABAs) as the preferred add-on therapy for adults and children over 5 years of age when asthma is inadequately controlled by inhaled corticosteroids alone. It has been suggested that LABA use may be associated with an increased risk of morbidity and mortality; however, this view is controversial since study findings have been inconsistent. While the safety profile of LABA monotherapy has been questioned, the value of concomitant inhaled corticosteroids to eliminate possible risks remains unproven. There is a paucity of efficacy and safety data for LABA use in children, and existing evidence is not sufficiently convincing to demonstrate a clear position for LABAs in the management of childhood asthma. The main aims of this article are to place LABAs in context in the management of childhood asthma and evaluate the current evidence for safety and efficacy.

Long-term safety of nebulized formoterol: Results of a twelve-month open-label clinical trial

Formoterol fumarate is a long-acting β2-agonist that is an effective bronchodilator for the maintenance management of patients with chronic obstructive pulmonary disease. The safety profile of the newly developed nebulized formoterol was evaluated over a twelve-month period in an open-label, active-control study. After completing a twelve-week double-blind double-dummy period, 569 subjects with chronic obstructive pulmonary disease entered an open-label extension study and received twice-daily 20 µg formoterol fumarate inhalation solution for nebulization (FFIS) or 12 µg formoterol fumarate dry powder inhalation (FA) for 52 weeks. Most of the FFIS-treated subjects (86%) completed at least six months of open-label treatment with over 90% compliance, comparable to the FA group (88%). Results of safety monitoring for adverse events, laboratory values, and cardiac changes were similar between treatment groups. Three hundred forty (73%) of FFIS-treated subjects and 83 (78%) of FA-treated subjects experienced an adverse event over the course of the study, the majority of which were mild to moderate and considered unrelated to treatment. COPD exacerbation occurred in 15.8% of FFIS-treated and 17.9% of FA-treated subjects. Deaths, serious adverse events, and discontinuations for adverse events occurred in 1.3, 16.2, and 5.4% of the nebulized group versus 1.9, 17.9, and 7.5% of the inhaled group, respectively. There were no clinically important changes from baseline in laboratory tests, including serum potassium and glucose, or vital signs and no treatment-related increases in cardiac arrhythmias, heart rate, or QTc prolongation. We conclude that nebulized formoterol fumarate twice daily is well tolerated over long-term treatment in moderate-to-severe COPD subjects and has a similar safety profile to the DPI formulation.