Functional and binding characteristics of long-acting beta 2-agonists in lung and heart

Identification and Characterization of Novel Bronchodilator Agonists Acting at Human Airway Smooth Muscle Cell TAS2R5

Bitter taste receptors (TAS2Rs) are recognized as being expressed on multiple cell types and organs, including human airway smooth muscle (HASM) cells, where agonists promote significant relaxation to constrictive stimuli. Thus, the HASM TAS2Rs have been targeted as novel bronchodilators for the treatment of asthma and other obstructive lung diseases. The TAS2R5 subtype, a dominant receptor on HASM, has few known agonists, all with reported low potency and efficacy. We screened multiple compounds by measuring [Ca²⁺]_i release in HASM (a consequence of receptor-G protein coupling) to establish structure-activity relationships and arrive at a potent agonist for TAS2R5. HASM physiological studies using magnetic twisting cytometry confirmed the relaxation effects of lead compounds. 1,10-Phenanthroline-5,6-dione had the greatest potency (EC₅₀ ≈ 120 nM), amounting to a >1000-fold improvement over the other compounds, and displayed maximal efficacy. These studies revealed critical structural requirements for favorable potencies and efficacies for a potential first-in-class bronchodilator targeting TAS2R5 of the airway.

The efficacy and safety of fluticasone propionate/formoterol compared with fluticasone propionate/salmeterol in treating pediatric asthma: a systematic review and meta-analysis

Objective

To evaluate the efficacy and safety of fluticasone propionate/formoterol (FP/FORM) versus fluticasone propionate/salmeterol (FP/SAL) in treating pediatric asthma during a 12-week treatment cycle.

Methods

Randomized controlled trials of FP/FORM compared with FP/SAL in treating pediatric asthma were searched systematically using Medline, Embase, and the Cochrane Controlled Trials Register.

Results

Two articles including 546 patients were evaluated. The FP/SAL group showed obvious improvements in pre-dose forced expiratory volume in 1 s (FEV₁) from day 0 to 84, asthma symptom scores, and sleep disturbance scores compared with the FP/FORM group; however, the FP/FORM group had improved peak expiratory flow rate (PEFR). In terms of 2-hour post-dose FEV₁ from day 0 to 84, 2-hour forced expiratory flow at 25%, 50%, and 75%, and 2-hour forced vital capacity, we observed no significant differences between the two groups. For safety, including patients with at least one adverse event, bronchitis, cough, or pharyngitis, both groups had similar incidences, differing only in incidence of nasopharyngitis.

Conclusion

Compared with FP/FORM, FP/SAL showed a clear improvement in pre-dose FEV₁, asthma symptom scores, and sleep disturbance scores. However, FP/FORM resulted in improved PEFR with a lower incidence of nasopharyngitis.

Why use long acting bronchodilators in chronic obstructive lung diseases? An extensive review on formoterol and salmeterol

Long-acting β2-adrenoceptor agonists, formoterol and salmeterol, represent a milestone in the treatments of chronic obstructive lung diseases. Although no specific indications concerning the choice of one molecule rather than another are provided by asthma and COPD guidelines, they present different pharmacological properties resulting in distinct clinical employment possibilities. In particular, salmeterol has a low intrinsic efficacy working as a partial receptor agonist, while formoterol is a full agonist with high intrinsic efficacy. From a clinical perspective, in the presence of low β2-adrenoceptors availability, like in inflamed airways, a full agonist can maintain its bronchodilatory and non-smooth muscle activities while a partial agonist may be less effective. Furthermore, formoterol presents a faster onset of action than salmeterol. This phenomenon, combined with the molecule safety profile, leads to a prompt amelioration of the symptoms, and allows using this drug in asthma as an "as needed" treatment in patients already on regular treatment. The fast onset of action and the full agonism of formoterol need to be considered in order to select the best pharmacological treatment of asthma and COPD.

Pathophysiological relevance of the cardiac β2-adrenergic receptor and its potential as a therapeutic target to improve cardiac function

β-adrenoceptors are members of the G protein-coupled receptor superfamily which play a key role in the regulation of myocardial function. Their activation increases cardiac performance but can also induce deleterious effects such as cardiac arrhythmias or myocardial apoptosis. In fact, inhibition of β-adrenoceptors exerts a protective effect in patients with sympathetic over-stimulation during heart failure. Although β(2)-adrenoceptor is not the predominant subtype in the heart, it seems to importantly contribute to the cardiac effects of adrenergic stimulation; however, the mechanism by which this occurs is not fully understood. This review summarizes the current knowledge on the role of β(2)-adrenoceptors in the regulation of cardiac contractility, metabolism, cardiomyocyte survival and cardiac arrhythmias. In addition, therapeutic considerations relating to stimulation of the β(2)-adrenoceptor such as an increase in cardiac contractility with low arrythmogenic effect, protection of the myocardium again apoptosis or positive regulation of heart metabolism are discussed.

Anti-inflammatory effects of β2 adrenergic receptor agonists in experimental acute lung injury

These studies were undertaken to extend emerging evidence that β(2) adrenergic receptor (β(2)AR) agonists, in addition to their bronchorelaxing effects, may have broad anti-inflammatory effects in the lung following onset of experimental acute lung injury (ALI). Young male C57BL/6 mice (25 g) developed ALI following airway deposition of bacterial LPS or IgG immune complexes in the absence or presence of appropriate stereoisomers (enantiomers) of β(2)AR agonists, albuterol or formoterol. Endpoints included albumin leak into lung and buildup of polymorphonuclear neutrophils and cytokines/chemokines in bronchoalveolar fluids. Both β(2)AR agonists suppressed lung inflammatory parameters (IC(50)=10(-7) M). Similar effects of β(2)AR agonists on mediator release were found when mouse macrophages were stimulated in vitro with LPS. The protective effects were associated with reduced activation (phosphorylation) of JNK but not of other signaling proteins. Collectively, these data suggest that β(2)AR agonists have broad anti-inflammatory effects in the setting of ALI. While β(2)AR agonists suppress JNK activation, the extent to which this can explain the blunted lung inflammatory responses in the ALI models remains to be determined.

Role of arformoterol in the management of COPD

Formoterol is a beta2-agonist that has both short and long acting bronchodilator effects. Beta2-agonists used as bronchodilators have been synthesized as racemates that comprise (R,R) and (S,S)-enantiomers. Compounds that are beta2-selective derive their bronchodilator effect from an interaction between the (R,R)-enantiomer and the beta2-adrenoceptor. Arformoterol is the (R,R)-enantiomer and is distinguished from the more commonly used racemic (RR/S,S)-diasteriomer of formoterol. Overall literature on the use of arformoterol in COPD is very preliminary. There is some in vitro data that demonstrate significant bronchodilation and inhibition of inflammation with arformoterol, and these effects may be more pronounced than those caused by racemic formoterol. There are limited clinical trial data that demonstrate that arformoterol produces significant improvement in lung function in COPD; however, many of the subjects involved had marked baseline airway reversibility. Arformoterol has been very well tolerated in clinical trials and could potentially be used only once every 24 hours (due to its prolonged effect). It can only be given in nebulized form. Arformoterol can potentially be given with other inhaled medications.

Therapeutic approaches for muscle wasting disorders

Muscle wasting and weakness are common in many disease states and conditions including aging, cancer cachexia, sepsis, denervation, disuse, inactivity, burns, HIV-acquired immunodeficiency syndrome (AIDS), chronic kidney or heart failure, unloading/microgravity, and muscular dystrophies. Although the maintenance of muscle mass is generally regarded as a simple balance between protein synthesis and protein degradation, these mechanisms are not strictly independent, but in fact they are coordinated by a number of different and sometimes complementary signaling pathways. Clearer details are now emerging about these different molecular pathways and the extent to which these pathways contribute to the etiology of various muscle wasting disorders. Therapeutic strategies for attenuating muscle wasting and improving muscle function vary in efficacy. Exercise and nutritional interventions have merit for slowing the rate of muscle atrophy in some muscle wasting conditions, but in most cases they cannot halt or reverse the wasting process. Hormonal and/or other drug strategies that can target key steps in the molecular pathways that regulate protein synthesis and protein degradation are needed. This review describes the signaling pathways that maintain muscle mass and provides an overview of some of the major conditions where muscle wasting and weakness are indicated. The review provides details on some therapeutic strategies that could potentially attenuate muscle atrophy, promote muscle growth, and ultimately improve muscle function. The emphasis is on therapies that can increase muscle mass and improve functional outcomes that will ultimately lead to improvement in the quality of life for affected patients.

Speed of onset of bronchodilator response to salbutamol inhaled via different devices in asthmatics: a bioassay based on functional antagonism

AIMS

To evaluate the speed of onset of bronchodilation following salbutamol administered via a metered-dose inhaler with a spacer (pMDI + Volumatic) and a dry-powder inhaler (Diskus), as well as the relative potencies of these devices in asthmatic patients with methacholine-induced bronchoconstriction.

METHODS

Eighteen patients inhaled methacholine (MCh) until FEV(1) decreased by 35% of control. Following administration of placebo, 200 microg salbutamol or 400 microg salbutamol through the pMDI + Volumatic or the Diskus, we calculated the time elapsed from drug administration and the appearance of a 90% increase in post-MCh forced vital capacity (FVC), FEV(1) and volume-adjusted mid-expiratory flow (recovery times). The salbutamol doses to be delivered by the two inhalation devices to achieve similar recovery times and the relative potencies of the devices were calculated by using the 2-by-2 Finney parallel regression method.

RESULTS

For all functional variables, recovery times were significantly (P < 0.01) shorter in pMDI + Volumatic than Diskus trials. The salbutamol doses to be delivered by the Diskus to achieve recovery times for FVC, FEV(1) and volume-adjusted mid-expiratory flow similar to those obtained with 200 microg salbutamol administered via the pMDI + Volumatic were 558 (95% CI 537, 579) microg, 395 (95% CI 388, 404) microg and 404 (95% CI 393, 415) microg, respectively, and corresponded to relative potencies of 2.79 (95% CI 2.68, 2.90), 1.98 (95% CI 1.94, 2.02), and 2.02 (95% CI 1.96, 2.07).

CONCLUSIONS

Administration of salbutamol via the pMDI + Volumatic provides faster reversal of induced bronchoconstriction than via the Diskus. The salbutamol dose targeting the lungs with the pMDI + Volumatic is approximately twice that with the Diskus.

Cardiac implications for the use of beta2-adrenoceptor agonists for the management of muscle wasting

There are proposals for the implementation of beta(2)-adrenoceptor agonists for the management of muscle wasting diseases. The idea has been initiated by studies in animal models which show that beta(2)-adrenoceptor agonists cause hypertrophy of skeletal muscle. Their use in clinical practice will also need an understanding of possible effects of activation of human heart beta(2)-adrenoceptors. Consequences could include an increased probability of arrhythmias in susceptible patients.

Systemic administration of beta2-adrenoceptor agonists, formoterol and salmeterol, elicit skeletal muscle hypertrophy in rats at micromolar doses

beta(2)-Adrenoceptor agonists provide a potential therapy for muscle wasting and weakness, but their use may be limited by adverse effects on the heart, mediated in part, by beta(1)-adrenoceptor activation. Two beta(2)-agonists, formoterol and salmeterol, are approved for treating asthma and have an extended duration of action and increased safety, associated with greater beta(2)-adrenoceptor selectivity. The pharmacological profiles of formoterol and salmeterol and their effects on skeletal and cardiac muscle mass were investigated in 12-week-old, male F344 rats. Formoterol and salmeterol were each administered via daily i.p. injection at one of seven doses (ranging from 1 to 2,000 microg kg(-1) day(-1)), for 4 weeks. Rats were anaesthetised and the EDL and soleus muscles and the heart were excised and weighed. Dose-response curves were constructed based on skeletal and cardiac muscle hypertrophy. Formoterol was more potent than salmeterol, with a significantly lower ED(50) in EDL muscles (1 and 130 microg kg(-1) day(-1), P <0.05), whereas salmeterol had greater intrinsic activity than formoterol in both EDL and soleus muscles (12% greater hypertrophy than formoterol). The drugs had similar potency and intrinsic activity in the heart, with a smaller leftward shift for formoterol than seen in skeletal muscle. A dose of 25 microg kg(-1) day(-1) of formoterol elicited greater EDL and soleus hypertrophy than salmeterol, but resulted in similar beta-adrenoceptor downregulation. These results show that doses as low as 1 microg kg(-1) day(-1) of formoterol can elicit significant muscle hypertrophy with minimal cardiac hypertrophy and provide important information regarding the potential therapeutic use of formoterol and salmeterol for muscle wasting.

Long-acting beta2-agonists: comparative pharmacology and clinical outcomes

Salmeterol and formoterol are both long-acting beta(2)-adrenoceptor agonists (beta(2)-agonists). They both provide excellent bronchodilating and bronchoprotective effects in patients with asthma but their are some differences between these two long-acting beta(2)-agonists in vitro and in vivo. Formoterol has a greater potency and intrinsic activity than salmeterol, which can become especially apparent at higher doses than that clinically recommended, and in contracted bronchi. Long-term use of long-acting beta(2)-agonists can induce tolerance, which can be partially reversed with corticosteroids. Long-acting beta(2)-agonists have some anti-inflammatory effects in vitro, but data in vivo are less convincing. Compared with doubling the dose of inhaled corticosteroids, the addition of inhaled long-acting beta(2)-agonists to inhaled corticosteroids improves symptom control in patients with asthma and reduces both the exacerbation rate of asthma and hospital admission rate. No enhanced airway responsiveness or loss of perception of dyspnea has been observed with the use of inhaled long-acting beta(2)-agonists. Monotherapy with long-acting beta(2)-agonists is not recommended.

Receptor imaging in the thorax with PET

This review focuses on positron emission tomography (PET)-imaging of receptors in the sympathetic and the parasympathetic systems of heart and lung and highlights the human applications of PET. For the alpha-adrenoceptor, only [11C]GB67 (N2-[6-[(4-amino-6,7-dimethoxy-2-quinazolinyl)(methyl)amino]hexyl]-N2-[11C]methyl-2-furamide hydrochloride) has been developed. Its potential for application in patients needs to be assessed. For both the beta-adrenergic and the muscarinic systems, potent PET radioligands have been prepared and evaluated in patients. It has been possible to measure receptor densities quantitatively in human heart [[11C]MQNB: [11C]methylquinuclidinyl benzilate, [11C]CGP12177: S-(3'-t-butylamino-2'-hydroxypropoxy)-benzimidazol-2-[11C]one and [11C]CGP12388: (S)-4-(3-(2'-[11C]isopropylamino)-2-hydroxypropoxy)-2H-benzimidazol-2-one] and qualitatively in lung [[11C]VC002: N-[11C]-methyl-piperidin-4-yl-2-cyclohexyl-2-hydroxy-2-phenylacetate and [11C]CGP12177]. Besides these subtype nonselective radioligands, the development of compounds that are selective for one subtype are ongoing and have not found successful application in humans yet.

Tocolytic effects of formoterol are associated with local change in the progesterone/estradiol ratio

OBJECTIVE

The aim of the study was to determine whether a beta(2)-adrenoceptor agonist, formoterol, inhibits premature delivery in connection with change in estradiol and progesterone concentrations in the amniotic fluid in ovariectomized rats.

STUDY DESIGN

Pregnant rats at the 15th day of gestation were bilaterally ovariectomized and given injection of 17beta-estradiol immediately after the operation and every 24 h. An osmotic pump filled with a solution of formoterol or saline was also implanted subcutaneously into the back of each. The animals were killed by decapitation under light ether anesthesia 18, 36, 54 or 72 h after ovariectomy, and the numbers of undelivered fetuses and newborn were counted. Amniotic fluid was collected 16, 36, and 54 h after ovariectomy.

RESULTS

Formoterol (0.15 mg/(kg h)) reversed the decline in premature delivered fetuses due to 17beta-estradiol 54 and 72 h after ovariectomy. Although no influence was evident regarding the progesterone and estradiol concentrations in amniotic fluid in ovariectomized rats supplemented with 17beta-estradiol, formoterol significantly inhibited the increment in the estradiol/progesterone ratio as well as the elevation in prostaglandin F2alpha concentration.

CONCLUSION

These findings indicate that tocolytic effects of formoterol may be associated with suppression of uterine activity due to modulation of hormone secretion.

In vitro aerosol performance and dose uniformity between the Foradile Aerolizer and the Oxis Turbuhaler

Dry powder inhalers for eformoterol fumarate dihydrate, a long-acting beta-2 agonist for bronchodilation, are currently available as the Foradile Aerolizer and the Oxis Turbuhaler. The two products are different in the formulation, the aerosol production mechanism, and the device resistance to air flow. These disparities are likely to lead to different aerosol characteristics. Our objective was to compare the in vitro performance of these two inhalers in producing eformoterol aerosols. Emitted dose uniformity was measured using a sampling apparatus described in the British Pharmacopaeia. Ten individual doses (dose number 2, 3, 15, 16, 30, 31, 45, 46, 59, and 60) of the entire content (60 doses) were collected from the Aerolizer and the Turbuhaler (six inhalers each). Particle size distribution of the aerosols generated by the two inhalers were measured by a multiple stage liquid impinger at four different air flows (30-120 L/min). Eformoterol collected from the sampling devices was measured by HPLC. Fine particles are those of < or = 1.7-5.0 microm in size in the aerosols obtained by interpolation of the data at the specified air flow. The Aerolizer showed a slight dependence of the emitted dose on the air flow, with the average emitted dose increased from 80% (at 30 L/min) to 90% (at higher flows) of the 12-microg label claim as compared with 60% for the Turbuhaler. When the emitted dose was normalized by the average emitted dose value, the Aerolizer showed less variation in the normalized emitted dose uniformity than the Turbuhaler. At high air flows, 90 and 120 L/min, both inhalers produced similar amounts (4 microg) of fine particles in the aerosol per dose discharged. As the flow as decreased to 30 and 60 L/min, both inhalers produced significantly less fine particles (p < 0.05), with the Oxis Turbuhaler producing lesser amounts than the Foradile Aerolizer. However, due to the different device resistance, comparing the inhaler performance at the same inspiratory effort may be more appropriate. At a comfortable effort of 40 cm H2O, the Foradile Aerolizer would produce a significantly higher fine particle mass in the aerosols. We conclude that the two inhalers were dissimilar in the emitted dose uniformity. The fine particle mass of eformoterol produced by the two inhalers was equivalent at high but not at low air flows. The disparities may be due to the difference in the formulation and the aerosol generation mechanism of the inhalers.

Features of asthma in the elderly

Asthma has been considered a rare disease in the elderly, but recent studies have shown that it is as common in the elderly as in the middle-aged population. Diagnosis of asthma is often overlooked in older patients, leading to undertreatment. Spirometry, determination of expiratory flow lability, and histamine challenge tests are tools that are as usefulfor the evaluation of elderly asthmatics as they areforyoungerpatients. Asthma is more severe in the elderly, especially in long-standing asthmatics. Treatment of asthma in the elderly should follow the same stepwise guidelines that are recommended for all age groups, though it will require more intense monitoring. An aggressive treatment approach to mild and moderate asthma in young people is the best hope of changing the future trends of asthma in the elderly.

Pharmacological similarities and differences between beta2-agonists

Formoterol and salmeterol are both long-acting bronchodilators that are effective in the treatment of asthma. However, some differences exist in their pharmacology that are reflected in their clinical profiles. Formoterol has a rapid onset of action, whereas salmeterol causes bronchodilation in a somewhat slower manner. However, both ofthese drugs are long-acting. After single doses clear effects are maintained for 12 h after inhalation, and with high doses effects are observed even at 24 h. Differences between the maximal effects of both drugs are also a consequence of their pharmacological properties. Thus, formoterol has higher intrinsic activity than salmeterol, which means that it is a full agonist, whereas salmeterol is a partial agonist on the beta2-receptor. Physicochemical properties of the drugs may explain the differences in onset and duration of action. Adequate water solubility and moderate lipophilicity of formoterol ensures rapid diffusion to the beta2-receptor on the smooth muscle and rapid bronchodilating activity. Salmeterol, on the other hand, may diffuse more slowly to the beta2-receptor because of its high lipophilicity explaining the slower onset of action. Unlike salbutamol, which is hydrophilic and has a rapid onset and short duration of action, both formoterol and salmeterol possess adequate lipophilic properties to remain in the airway tissues as a depot in close vicinity to the beta2-receptor, explaining their long duration of effect. The long duration of salmeterol has also been suggested to depend on an anchored binding within the beta2-receptor. The pharmacological evidence for a rapid onset of action of formoterol, but long duration of effect, is supported by several clinical studies. The fast onset of bronchodilation and high intrinsic activity of formoterol therefore suggest that it can be used for relief treatment in patients with asthma if they are concomitantly treated with inhaled glucocorticoids.

Chronic systemic administration of salmeterol to rats promotes pulmonary beta(2)-adrenoceptor desensitization and down-regulation of G(s alpha)

1. The aim of the present study was to examine the effects of chronic infusion of the long-acting agonist salmeterol on pulmonary beta(2)-adrenoceptor function in Sprague-Dawley rats in vivo and to elucidate the molecular basis of any altered state. 2. Systemic administration of rats with salmeterol for 7 days compromised the ability of salmeterol and prostaglandin E(2) (PGE(2)), given acutely by the intravenous route, to protect against ACh-induced bronchoconstriction when compared to rats treated identically with vehicle. 3. beta(1)- and beta(2)-adrenoceptor density was significantly reduced in lung membranes harvested from salmeterol-treated animals, which was associated with impaired salmeterol- and PGE(2)-induced cyclic AMP accumulation ex vivo. 4. Three variants of G(s alpha) that migrated as 42, 44 and 52 kDa peptides on SDS polyacrylamide gels were detected in lung membranes prepared from both groups of rats but the intensity of each isoform was markedly reduced in rats that received salmeterol. 5. The activity of cytosolic, but not membrane-associated, G-protein receptor-coupled kinase was elevated in the lung of salmeterol-treated rats when compared to vehicle-treated animals. 6. The ability of salmeterol, administered systemically, to protect the airways of untreated rats against ACh-induced bronchoconstriction was short-acting (t(off) approximately 45 min), which contrasts with its long-acting nature when given to asthmatic subjects by inhalation. 7. These results indicate that chronic treatment of rats with salmeterol results in heterologous desensitization of pulmonary G(s)-coupled receptors. In light of previous data obtained in rats treated chronically with salbutamol, we propose that a primary mechanism responsible for this effect is a reduction in membrane-associated G(s alpha). The short-acting nature of salmeterol, when administered systemically, and the reduction in beta-adrenoceptor number may be due to metabolism to a biologically-active, short-acting and non-selective beta-adrenoceptor agonist.

Tocolytic effects of a long-acting beta2-adrenoceptor agonist, formoterol, in rats

We have assessed the tocolytic activity of formoterol, a novel long-acting and potent beta2-adrenoceptor agonist, through its production of cyclic adenosine monophosphate, in comparison with ritodrine, a beta2-adrenoceptor agonist used clinically to counter premature delivery. Formoterol and ritodrine inhibited the amplitude and frequency of rat uterine contraction, with IC50 values of 3.8 x 10(-10) and 4.7 x 10(-7) M, respectively. Intravenous administration of formoterol or ritodrine caused inhibition of uterine motility and increased heart rate in a dose-dependent manner. Inhibition of uterine motility by oral administration of formoterol (0.3 and 1 mg kg(-1)) continued for at least 60 min, whereas that with ritodrine (100 mg kg(-1)) persisted for 15 min with rapid recovery thereafter in pregnant rats. The beta-adrenoceptor binding of [125I]iodopindolol to the myometrium of pregnant rats was competitive with formoterol and ritodrine, with Ki values of 0.04 and 6.10 nM, respectively. Formoterol (10(-6)-10(-4) M) and ritodrine (10(-6)-10(-4) M) increased the level of cyclic adenosine monophosphate in lymphocytes in a dose-dependent manner. The results suggested that formoterol caused relaxation of uterine motility through production of cyclic adenosine monophosphate. Thus, formoterol may be useful as a treatment to counter premature delivery.

Systemic effects of formoterol and salmeterol: a dose-response comparison in healthy subjects

BACKGROUND

The main adverse effects of inhaled long acting beta(2) agonists relate to their systemic activity. The systemic effects seen over eight hours after inhalation of three doses of salmeterol and formoterol were therefore compared in normal subjects.

METHODS

A double blind, randomised, crossover study was carried out in 16 healthy subjects who inhaled formoterol 24, 48 and 96 microg (via Turbuhaler((R))), salmeterol 100, 200 and 400 microg (via Diskhaler((R))), or placebo on separate days. Heart rate, systolic and diastolic blood pressure, and plasma potassium and glucose concentrations were measured for eight hours following each drug and mean values were used to plot the time course of change after each dose. Mean maximum (or minimum) absolute values were used to construct dose-response curves to calculate the relative dose potency of the two drugs. Lunch was taken after the four hour readings and, since this caused additional changes to the main outcome measures, data from the first four hours are also presented in a post hoc analysis.

RESULTS

Both salmeterol and formoterol caused an early dose dependent increase in heart rate and glucose concentrations and a fall in diastolic blood pressure and plasma potassium concentration; formoterol also caused an early increase in systolic blood pressure. The cardiovascular effects occurred more rapidly than the metabolic effects and the response to formoterol was faster than that of salmeterol, apart from the glycaemic response. The effects of salmeterol were slightly more prolonged than those of formoterol, although some dose related effects were apparent at eight hours with both drugs. The relative dose potency for formoterol compared with salmeterol at four and eight hours for the different end points excluding systolic blood pressure ranged from 1.6 to 7.0 after adjusting for baseline values. Relative dose potencies (95% CI) for maximum heart rate and plasma potassium concentrations were 4.1 (3.0 to 5.6) and 5.8 (4.1 to 8.6) over four hours and 2.4 (1.2 to 3.8) and 3.0 (1.2 to 5.7) over eight hours.

CONCLUSIONS

Formoterol and salmeterol cause dose related changes in heart rate, diastolic blood pressure, and plasma glucose and potassium concentrations. Formoterol has a more rapid onset for most end points whereas salmeterol has slightly more prolonged activity. Both drugs have a relatively modest therapeutic window. The relative dose potencies of the two drugs for the main end points were similar to the fourfold difference in recommended doses. Some differences in the pharmacological profile of the two drugs emerged and are as yet unexplained.

Is beta-adrenergic-mediated airway relaxation of salmeterol antagonized by its solvent xinafoic acid?

STUDY OBJECTIVE

Isolated case reports of asthmatic fatalities accompanied by the use of salmeterol have raised the question whether a paradoxical effect of salmeterol or its vehicle on the airways might contribute to these fatalities. We questioned whether salmeterol's solvent, xinafoic acid, has detrimental effects on the tone of airways or on beta-adrenoceptor binding.

MATERIALS AND METHODS

Basenji-greyhound dogs were anesthetized and their peripheral airways challenged with xinafoic acid via a wedged bronchoscope technique. Radioligand binding assays were performed in lung membranes prepared from these dogs.

RESULTS

In contrast to a methacholine control, xinafoic acid (0.001 to 1.0 mg/mL) aerosolized into the peripheral airways of anesthetized dogs did not increase airway resistance. Xinafoate alone had no significant effect on the specific binding of 125I-cyanopindolol to lung membranes and did not affect the affinity of salmeterol for the beta-adrenoceptor in the absence or presence of xinafoate, respectively (-log concentration that inhibits 50% [IC50] of the high-affinity site, 7.7+/-0.15 and 7.9+/-0.27; -log IC50 of the low-affinity site = 5.6+/-0.44 and 5.3+/-0.28 [n = 4]).

CONCLUSION

These findings suggest that xinafoic acid, the solvent for salmeterol, does not have direct airway irritant effects, does not bind to beta-adrenoceptors, and does not impair the binding of salmeterol to beta-adrenoceptors. Thus, xinafoate is unlikely to contribute to the worsening of airway symptoms in asthmatics using salmeterol xinafoate.

Characterisation of beta2-adrenoceptors, using the agonist [11C]formoterol and positron emission tomography

The agonist radioligand N-[2-hydroxy-5-[1-hydroxy-2-[[2-(4-[11C]-methoxyphenyl)-1-methylethyl]am ino]ethyl]phenyl]formamide ([11C]formoterol) was synthesised in order to test its ability to visualise pulmonary beta2-adrenoceptors in vivo, with positron emission tomography (PET). Formoterol was labelled via reaction of a dibenzyl-protected precursor with [11C]CH3I. Subsequent deprotection with Pd/C and H2 yielded [11C]formoterol in 5-15% (corrected for decay) and the specific activity ranged from 5.5-22.2 TBq mmol (150-600 Ci mmol(-1)), 60-70 min after end of bombardment. Biodistribution studies with [11C]formoterol were performed in male Wistar rats which were either untreated or predosed with (D,L)-propranolol hydrochloride (2.5 mg kg(-1), beta-adrenoceptor antagonist), erythro-DL-1-(7-methylindan-4-yloxy)-3-isopropylaminobuta n-2-ol hydrochloride (ICI 118551, 0.15 mg kg(-1), beta2-adrenoceptor antagonist), isoprenaline (15 mg kg(-1), non-subtype selective beta-adrenoceptor agonist) or (+/-)-(2-hydroxy-5-[2-((2-hydroxy-3-(4-((1-methyl-4-trifluoromethyl)1H-i midazol-2-yl-)phenoxy)propyl)amino)ethoxy]benzamide)monomethane sulfonate (CGP 20712A, 0.15 mg kg(-1), beta1-adrenoceptor antagonist). Lungs, heart, liver and plasma were analysed for radioactive metabolites. The kinetics of [11C]formoterol in the lungs of male Wistar rats were investigated by means of a dynamic PET study. The biodistribution studies showed significant specific binding in tissues known to contain beta2-adrenoceptors (lungs, spleen, and heart). Binding in these organs was blocked by ICI 118551 and isoprenaline, but not by CGP 20712A. [11C]Formoterol was rapidly metabolised in rats but lungs and heart did not substantially take up the labelled metabolites. The binding of [11C]formoterol in various tissues of rats is consistent with the beta2-selectivity of formoterol. Whether [11C]formoterol selectively binds to the high affinity state of beta2-adrenoceptors remains to be elucidated. [11C]Formoterol is potentially useful for studying beta2-adrenoceptors with PET and this radioligand may provide new insights in the mechanisms underlying prolonged sympathomimetic action.

Long-acting inhaled beta2-agonists in asthma therapy

OBJECTIVE

To review the pharmacology of the long-acting inhaled beta2-agonists, salmeterol and formoterol, summarize results of their clinical trials, evaluate their safety records, and discuss their roles in the treatment of asthma.

DATA SOURCES

Preclinical and clinical studies involving salmeterol or formoterol were identified by a MEDLINE search, weekly computerized literature updates, and manual searches. Studies of satisfactory quality were chosen for review.

DATA SYNTHESIS

Salmeterol and formoterol are potent and selective beta2-adrenoceptor agonists with durations of action >12 h. Their major differences are that formoterol has a rapid onset of action and is a partial agonist of high intrinsic efficacy, whereas salmeterol has a delayed onset and is a partial agonist of low intrinsic efficacy. Twice daily use of either drug results in improved lung function, reduced symptoms, and a better quality of life. These agents protect against exercise-induced asthma for 12 h and eliminate nighttime awakening in most patients. Limited tolerance develops, especially to their bronchoprotective effects, but their improvement of lung function is sustained.

CONCLUSIONS

Regular use of salmeterol or formoterol provides subjective and objective amelioration of asthma in patients experiencing excessive symptoms or physiologic impairment despite the regular administration of low doses of inhaled corticosteroids (equivalent to approximately 500 microg/d of beclomethasone). Intermittent use of either long-acting beta2-agonist can provide prolonged protection against exercise-induced asthma or nighttime symptoms. Patients should be instructed to continue taking inhaled steroids when long-acting beta2-agonists are administered on a regular schedule and to not take long-acting beta2-agonists between regularly scheduled doses. Used properly, they are effective and safe adjunctive agents in the treatment of asthma.

Time course and relative dose potency of systemic effects from salmeterol and salbutamol in healthy subjects

BACKGROUND

The main adverse effects of beta 1 agonists relate to their systemic activity. The time course and dose response relations of the systemic effects of salmeterol compared with salbutamol were investigated.

METHODS

A double blind, randomised, crossover study was carried out in 14 healthy subjects who attended on seven days. Heart rate, QTc interval, blood pressure, plasma potassium and glucose concentrations were measured for four hours following inhaled placebo, salmeterol 100, 200 and 400 micrograms and salbutamol 600, 1200 and 2400 micrograms given by metered dose inhaler. Maximum changes from baseline and maximum absolute values following each dose of treatment were used to construct log dose response curves and calculate relative dose potency.

RESULTS

Both salmeterol and salbutamol caused dose dependent changes in heart rate, QTc interval, and plasma potassium and glucose concentrations. The onset of cardiac effects was rapid following both drugs, whereas changes in glucose and potassium concentrations occurred more gradually with salmeterol. The increase in heart rate and fall in potassium level were sustained over the four hours whereas glucose levels gradually returned towards baseline. The relative dose potency of salmeterol compared with salbutamol for changes from baseline was 7.1 (95% CI 3.9 to 14.4) for the QTc interval and 8.2 (95% CI 5.7 to 12.6) for plasma potassium concentration. Salmeterol caused steeper dose response curves for heart rate and plasma glucose concentration than salbutamol so relative dose potency values could not be calculated.

CONCLUSIONS

These findings support previous data that salmeterol 100 micrograms is broadly equivalent to salbutamol 800 micrograms for systemic effects. The greater systemic effects of salmeterol are most likely to be due to greater potency relative to dose, although it may also have greater systemic bioavailability. The steeper dose response curve for heart rate with salmeterol indicates that it has a narrower therapeutic window than salbutamol and thus should be prescribed at the lowest effective dose.