The pharmacology of salmeterol

Exercise-induced asthma in children

Exercise-induced asthma (EIA) is a relatively common problem in children, but may not be recognized because children either do not report their symptoms, or avoid activities that cause it. Clarifying the diagnosis of EIA, in particular separating EIA from other causes of exertional dyspnea, is essential. Treating EIA in children is challenging because of the nature of their physical activities, which are often not planned, and may be prolonged. Keeping children active is an important goal to ensure healthy physical and social development. Many children with EIA are well managed with an inhaled short-acting beta(2)-adrenoceptor agonist before exercise or if symptoms develop. The approach to more troublesome EIA depends on whether the child has persistent asthma and requires better prevention, or the EIA is an isolated clinical problem. The options for treatment also depend on the timing, frequency, and duration of activity that induces EIA. Options include the addition of a cromone, a leukotriene modifier, an inhaled corticosteroid, or switching to use a long-acting beta(2)-adrenoceptor agonist. The use of warm-up exercises has been shown to be helpful by using the refractory period but is not practical for most children with EIA. A final consideration for successful management of EIA in children is that the delivery of medication needs to be age-appropriate.

Beta-agonists

Beta-Agonists are a mainstay of asthma treatment. Short-acting beta-agonists are the most effective bronchodilators for rescue or quick relief of symptoms. Long-acting beta-agonists have a key role in long-term control when added to inhaled corticosteroid therapy, and are especially useful in the control of nocturnal asthma. Both types of beta-agonists may be used in the prophylaxis of exercise-induced asthma with long-acting beta-agonists providing more prolonged protection. beta-Agonists have minimal side effects and are safe when used appropriately.

Stimulation of beta-adrenoceptors activates astrocytes and provides neuroprotection

Our previous studies established that induction of growth factor synthesis and neuroprotection by the beta(2)-adrenoceptor agonist clenbuterol in vitro and in vivo was associated with the activation of astrocytes, the major source of trophic factors in the brain. In the present study, we further investigated the specificity of beta(2)-adrenoceptor-mediated effects on astrocyte activation and neuroprotection. In mixed hippocampal cultures neuroprotection against glutamate-induced cell death by clenbuterol (1 microM) was blocked by the beta(1/2)-adrenoceptor antagonist propranolol and the specific beta(2)-adrenoceptor antagonists 1-[2,3-(Dihydro-7-methyl-1H-inden-4-yl)-oxy]-3-[(1-methylethyl)-amino]-2-butanol (ICI 118,551, 10 microM) and butoxamine (10 microM), while the beta(1)-adrenoceptor-selective antagonist metoprolol (10 microM) showed no effect. The beta(2)-adrenoceptor agonists clenbuterol (1-100 microM) and salmeterol (0.01-1 microM) induced profound morphological changes of cultured astrocytes which transformed into activated astroglia with pronounced dendrite-like processes. This phenomenon was blocked by butoxamine (1 mM) and propranolol (10 microM), but not by metoprolol (10 microM). However, similar morphological changes in astrocytes were also observed after stimulation of beta(1)-adrenoceptors by dobutamine (1-10 microM) and norepinephrine (1-10 microM). This effect was blocked by propranolol (10 microM) and metoprolol (10 microM) but not by butoxamine (1 mM), suggesting that stimulation of either beta(1)- or beta(2)-adrenoceptors was sufficient to induce activation of astrocytes. In addition, beta(1)-adrenoceptor stimulation by dobutamine (1-10 microM) protected hippocampal neurons against glutamate toxicity. In a model of focal cerebral ischemia in mice the cerebroprotective effect of clenbuterol (0.3 mg/kg) was blocked by propranolol (5 mg/kg) and butoxamine (5 mg/kg). Interestingly, the infarct size was reduced after co-treatment with clenbuterol (0.3 mg/kg) and metoprolol (5 mg/kg) as compared to clenbuterol treatment (0.3 mg/kg) alone. In conclusion, activation of astrocytes and neuroprotection can be achieved by stimulation of either beta(1)- or beta(2)-adrenoceptors in vitro, whereas in vivo neuroprotection is preferentially mediated through beta(2)-adrenoceptors.

Clinical pharmacokinetics of salmeterol

Salmeterol is an inhaled long-acting selective beta(2)-adrenoceptor agonist that is commercially available as the xinafoate (1-hydroxy-2-naphthoic acid) salt of the racemic mixture of the two optical isomers, (R)- and (S)-, of salmeterol. It acts locally in the lung through action on beta2 receptors. Limited data have been published on the pharmacokinetics of salmeterol. Moreover, there are no data on the extent to which inhaled salmeterol undergoes first-pass metabolism. This lack of information is most likely due to the very low plasma concentrations reached after inhalation of therapeutic doses of salmeterol and the problems in developing an analytical method that is sensitive enough to determine these concentrations. When salmeterol is inhaled, plasma concentrations of the drug often cannot be detected, even at 30 minutes after administration of therapeutic doses. Larger inhaled doses give approximately proportionally increased blood concentrations. Plasma salmeterol concentrations of 0.1 to 0.2 and 1 to 2 microg/L have been attained in healthy volunteers about 5 to 15 minutes after inhalation of a single dose of 50 and 400 microg, respectively. In patients who inhaled salmeterol 50microg twice daily for 10 months, a second peak concentration of 0.07 to 0.2 microg/L occurred 45 to 90 minutes after inhalation, probably because of the gastrointestinal absorption of the swallowed drug. Salmeterol xinafoate dissociates in solution to salmeterol and 1-hydroxy-2-naphthoic acid. These two compounds are then absorbed, distributed, metabolised and excreted independently. The xinafoate moiety has no apparent pharmacological activity, is highly protein bound (>99%), largely to albumin, and has a long elimination half-life of about 12 to 15 days in healthy individuals. For this reason, it accumulates in plasma during repeated administration, with steady-state concentrations reaching about 80 to 90 microg/L in patients treated with salmeterol 50microg twice daily for several months. The cytochrome P450 (CYP) isoform 3A4 is responsible for aliphatic oxidation of salmeterol base, which is extensively metabolised by hydroxylation with the major metabolite being alpha-hydroxysalmeterol, with subsequent elimination predominantly in the faeces. It has been demonstrated that 57.4% of administered radioactivity is recovered in the faeces and 23% in the urine; most is recovered between 24 and 72 hours after administration. Unchanged salmeterol accounts for <5% of the excreted dose in the urine. Since the therapeutic dose of salmeterol is very low, it is unlikely that any clinically relevant interactions will be observed as a consequence of the coadministration of salmeterol and other drugs, such as fluticasone propionate, that are metabolised by CYP3A. All the available data clearly show that at the recommended doses of salmeterol, systemic concentrations are low or even undetectable. This is an important point, because it has been demonstrated that the systemic effects of salmeterol are more likely to occur with higher doses, which lead to approximately proportionally increased blood concentrations.

Use of a long-acting inhaled beta2-adrenergic agonist, salmeterol xinafoate, in patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a condition in which continuous bronchodilation may have clinical advantages. This study evaluated salmeterol, a beta-agonist bronchodilator with a duration of action substantially longer than that of short-acting beta-agonists, compared with ipratropium, an anticholinergic bronchodilator, and placebo in patients with COPD. Four hundred and five patients with COPD received either salmeterol 42 microg twice daily, ipratropium bromide 36 microg four times daily, or placebo for 12 wk in this randomized, double-blind, parallel-group study. Patients were stratified on the basis of bronchodilator response to albuterol (> 12% and > 200-ml improvement) and were randomized within each stratum. Bronchodilator response was measured over 12 h four times during the treatment period. Salmeterol provided similar maximal bronchodilatation to ipratropium but had a longer duration of action and a more constant bronchodilatory effect with no evidence of bronchodilator tolerance. Both active treatments were well tolerated. Salmeterol was an effective bronchodilator with a consistent effect over this 12-wk study in patients with COPD, including those "unresponsive" to albuterol. The long duration of action of salmeterol offers the advantage of twice daily dosing compared with the required four times a day dosing with ipratropium.

A one-week dose-ranging study of inhaled salmeterol in children with asthma

This was a 1-week study evaluating the safety and efficacy of two dosage regimens of salmeterol in children with asthma. A total of 243 children, aged 4-11 years, with mild-to-moderate asthma were enrolled in a randomized, double-blind, placebo-controlled, parallel-group, multicenter study evaluating salmeterol xinafoate 21 micrograms and 42 micrograms administered via metered-dose inhaler (MDI) twice daily for 1 week. Patients were allowed to use albuterol MDI as needed for relief of acute symptoms. Inhaled corticosteroids and/or cromolyn at fixed dosages could be continued during the study, but theophylline and oral beta-agonists were not allowed. Twelve-hour serial spirometry (for patients aged 6-11 years) and serial peak expiratory flow rate (PEFR) (all patients) were performed on days 1 and 8 of treatment; morning and evening PEFR were recorded each day prior to inhalation of the study drug. Safety was assessed by monitoring adverse events, clinical laboratory values, vital signs, electrocardiogram (ECG), and 24-hr ECG (Holter) monitoring. Both the 21-micrograms and 42-micrograms doses of salmeterol produced significantly greater bronchodilation, as measured by 12-hr serial forced expiratory volume in 1 sec (FEV1) (p < or = 0.02) and PEFR (p < or = 0.001), than did placebo on days 1 and 8. A small dose-response was observed, with the 42-micrograms dosage producing consistently higher serial FEV1 and PEFR than did the 21-micrograms dosage, although the differences were not statistically significant. Morning and evening PEFR increased significantly (p < or = 0.008) with both dosages of salmeterol compared with placebo. Twelve patients (5%) experienced potentially drug-related adverse events, with headache (4% in each salmeterol group) being the most common. There were no clinically significant changes in heart rate as measured by Holter monitoring, ECGs, vital signs, or clinical laboratory values following treatment with either dose of salmeterol. Salmeterol 21 micrograms or 42 micrograms twice daily was effective in producing bronchodilation in children aged 4-11 years, and both dosages had good safety profiles. Patients treated with salmeterol 42 micrograms twice daily showed a trend toward greater improvement in asthma control compared with those who received salmeterol 21 micrograms.

Beta2-adrenoceptors: mechanisms of action of beta2-agonists

The human beta2-adrenoceptor is a member of the 7 transmembrane family of receptors. It is encoded by a gene on chromosome 5 and is widely distributed in the respiratory tract. Following beta2-adrenoceptor activation, intracellular signalling is mainly produced by inducing cyclic AMP. This produces airway relaxation through phosphorylation of muscle regulatory proteins and modification of cellular Ca2+concentrations. Beta2-agonists have been characterised into those which directly activate the receptor (salbutamol/terbutaline), those which are taken up into a membrane depot (formoterol) and those which interact with a receptor-specific, auxiliary binding site (salmeterol). These differences in mechanism of action are reflected in the kinetics of airway smooth muscle relaxation and bronchodilation in asthmatic patients. Beta-adrenoceptor desensitisation is associated with beta2-agonist activation and differs depending on the cell type. It is reflected in the different profiles of clinical tolerance to chronic beta2-agonist therapy. A number of polymorphisms of the beta2-receptor have been described which appear to alter the behaviour of the receptor, including the degree of downregulation and response to beta2-agonists.

Serum potassium levels, CPK-MB and ECG in children suffering asthma treated with beclomethasone or beclomethasone-salmeterol

Asthma morbidity and mortality has increased. One of the possible causes is the excessive use of beta agonists. The aim of this study is to compare the effects of six week treatment with beclomethasone alone (Ibec) or the combination of beclomethasone-salmeterol (Ibe + Isal) on serum potassium (K), CPK-MB and ECG in children suffering asthma. It was a prospective, randomised, open cross-over trial. Patients received either Ib2 (2 puff/12 hr, 100 micrograms per puff) or Ibe + Isal (B 2 puff/12 hr, 100 micrograms per puff and S 2 puff/12 hr, 25 micrograms per puff) with dose meter inhaler by 6 weeks, with a four-week wash-out period between the treatments. K, CPK-MB and ECG were assessed at baseline, and after each treatment period. There were 9 girls and 20 boys, aged 11 +/- 2.18 (mean +/- SD) years, baseline K was 4.57 +/- 0.43 mEq/l, after B K 4.38 +/- 0.39 IU and after BS K 4.38 +/- 0.40. The CPK-MB level were baseline 14.75 +/- 4.5, after B 20.10 +/- 6.9 and after BS 21 +/- 8.05 (p < 0.05). Baseline QTc was 0.416 +/- 0.02 msec, after B 0.425 +/- 0.027, and after BS 0.415 +/- 0.029. We conclude that the treatment of children with asthma with 400 micrograms per day of Ibec or concomitantly with 100 micrograms of Isal for 6 weeks does not alter the serum K+ or the QTc. However, the CPK-MB has a significant increment with both treatments but without clinical and/or ECG changes. We can't affirm that Ibec or Ibec plus Isal have a cardiotoxic side-effect by the only presence of high levels of CPK-MB. We agree that it is necessary a close follow up of these apparently asymptomatic patients not induce important cardiovascular changes although CPK-MB was increased.

Biochemical and functional characterization of 1-benzyl substituted trimetoquinol affinity analogs on rat and human beta-adrenoceptors

The site of interaction for the 1-(3',4',5'-trimethoxybenzyl) group of trimetoquinol (TMQ) with beta-adrenoceptors (beta-ARs) is important for the rational design of highly potent and beta3-AR-selective analogs. 1-Benzyl ring-substituted TMQ analogs were evaluated for binding affinities and biochemical activities (cyclic AMP accumulations) in Chinese hamster ovary (CHO) cells expressing the rat and human beta3-AR, and for functional activities on isolated rat tissues. Binding affinities (K1 approximately 0.055 to 1.5 microM) for the rat beta3-AR and potencies for adenylyl cyclase activation (K(act) approximately 0.43 to 2;5 nM) of the 3'-monoiodo or 3',5'-diiodo derivatives with 4'-isothiocyanato-, 4'-amino, 4'-acetamido, or 4'-alpha-haloacetamido substitutions were higher than those of (-)-isoproterenol, and comparable to those of BRL 37344 [(+/-)-(R*,R*-[4-[2-[[2-(3-chlorophenyl)-2-hydroxy-ethyl]amino]propyl]ph enoxy]-acetic acid sodium]. A similar rank order of binding affinities (K(i) approximately 0.11 to 2.5 microM) and potencies (K(act) approximately 0.45 to 9.5 nM) was obtained for TMQ analogs on the human beta3-AR. The 4'-acetamido and 4'-alpha-chloroacetamido analogs of 3',5'-diiodoTMQ were more potent than (-)-isoproterenol in rat atria (beta1-AR) and rat trachea (beta2-AR) and exhibited partial agonist activities, whereas full agonist activities were observed in rat esophageal smooth muscle (EC50 approximately 2-8 nM, beta3-AR). 4'-alpha-Chloroacetamido-3',5'-diiodoTMQ-mediated chronotropic responses in atria were sustained and resistant to washout. Further, the 4'-alpha-chloroacetamido and 4'-alpha-bromoacetamido analogs of 3',5'-diiodoTMQ demonstrated significant concentration-dependent irreversible binding to the rat beta3-AR. Reversible beta-AR agonists such as (-)-isoproterenol, BRL 37344, and 4'-acetamido-3',5'-diiodoTMQ or nucleophilic 1-amino acids (lysine, glutathione, cysteine) did not protect against this irreversible binding. Thus, the lipophilic 1-benzyl ring of TMQ analogs interacts with a hydrophobic region of the beta-AR that may represent an exo-site or an allosteric binding site.

Effects of salmeterol on secretion of phosphatidylcholine by alveolar type II cells

Beta-adrenergic agents enhance secretion of phosphatidylcholine (PC) by adult and fetal type II cells. We have previously shown that terbutaline stimulates secretion of PC by fetal type II cells, but the response wanes after 30 minutes. We studied the effects of salmeterol, a highly selective, long-acting beta2-adrenergic agonist that does not cause receptor desensitization, on PC secretion by adult type II alveolar cells in primary culture. Release of lactate-dehydrogenase was < 4% and did not vary with the concentration of salmeterol. Salmeterol stimulated PC secretion in a concentration-dependent manner. The maximum effective-concentration tested was 50 nM and the EC50 was 11.40 +/- 1.14 nM. Propranolol inhibited the effect of salmeterol on release of PC, confirming that the effects of salmeterol are mediated by beta-receptors. OT50, the time for onset of action, was 32.0 +/- 1.6 minutes. RT50, the time to achieve 50% recovery from maximal stimulation was, 393.0 +/- 20.2 minutes. We conclude that salmeterol stimulates PC secretion by type II cells through activation of beta-adrenergic receptors and has a longer duration of action (>6 hours) compared to other beta2-agonists. Salmeterol may be a useful drug with which to study the role of receptor desensitization in the developmental changes in PC secretion.

Long-acting beta(2)-agonists in management of childhood asthma: A critical review of the literature

This review assesses the evidence regarding the use of long-acting beta(2)-agonists in the management of pediatric asthma. Thirty double-blind, randomized, controlled trials on the effects of formoterol and salmeterol on lung function in asthmatic children were identified. Single doses of inhaled salmeterol or formoterol cause prolonged bronchodilatation (>12 h) and extended bronchoprotection against exercise-induced bronchoconstriction in children, some children achieving full protection for more than 12 h. Heterogeneity in bronchoprotection has been observed, and individual dose-titration may be attempted. The onset of action of formoterol is comparable to salbutamol, while salmeterol has a slower onset of action. Partial tolerance develops when long-acting beta(2)-agonists are used as regular treatment, including cross-tolerance to short-acting beta(2)-agonists. Regular treatment with salmeterol in children with or without corticosteroids provides statistically significant bronchodilatation, but the degree of improvement in lung function or bronchoprotection against exercise and nonspecific irritants is small with regular use. There is no evidence of anti-inflammatory effects from inhaled long-acting beta(2)-agonists, which is reflected by unchanged or increased bronchial hyperreactivity and no reduction of exacerbation rates. The evidence does not support a recommendation for long-acting beta(2)-agonists as monotherapy, nor does it support their general use as regular add-on therapy. In conclusion, long-acting beta(2)-agonists provide effective bronchodilatation and bronchoprotection when used as intermittent, single-dose treatment of asthma in children, but not when used as regular treatment. Future studies should examine the positioning of long-acting beta(2)-agonists as an "as needed" rescue medication instead of short-acting beta(2)-agonists for pediatric asthma management.

Effect of inhaled beta 2 adrenoceptor agonist, albuterol sulphate, on performance of horses

This study was designed to test the hypothesis that a specific beta 2 adrenergic receptor agonist, albuterol sulphate, when delivered by metered-dose inhaler (MDI) would affect the performance of Thoroughbred horses during incremental exercise testing. Six conditioned Thoroughbred horses were randomly assigned to one of 2 treatment groups: Group 1 horses received placebo and Group 2 received albuterol. Each horse received both treatments in a crossover design with a 3 week interval between trials. Horses inspired albuterol (900 micrograms) or placebo over a 5 min period followed by an incremental, peak oxygen consumption (VO2peak) exercise test. Facial arterial blood gases (PaO2, PaCO2), pHa, temperature, haemoximetry (O2Hb, COHb, MetHb, RHb) and electrolytes (Na+, K+, iCa2+, Cl-) were measured. Heart rate (HR), VO2peak, CO2 production (VCO2), plasma lactate, speed at failure, exercise duration, and urine levels of albuterol and metabolites (Alburine) were monitored. The Paratrend7 intravascular sensor provided continuous arterial blood gas data. Mixed effects linear modelling using generalised least-squares estimation was used to assess treatment and speed main effects interaction. Significant differences (P < 0.01) were found between placebo and albuterol-treated horses for total run time (mean +/- s.e. 405.8 +/- 8.8 vs. 430.5 +/- 6.7 s) and run time from completion of 8 m/s until fatigue (169.3 +/- 8.6 vs. 187.3 +/- 6.7 s), as well as VO2peak (121.7 +/- 3.7 vs. 130.3 +/- 3.8 ml/kg/min), respectively. In conclusion, inhaled albuterol sulphate has a small but significant effect on the performance of fit Thoroughbred horses during incremental, VO2peak exercise testing.

Enantiomers of bronchodilating beta2-adrenoceptor agonists: is there a cause for concern?

All bronchodilating beta2-adrenoceptor agonists in current clinical use are derivatives of adrenaline and are available as racemates. Whereas the vast majority of the pharmacologic and clinical documentation has been made with the racemates, there are a few studies with the individual enantiomers. It thus appears that all established pharmacologic effects of racemic beta2-agonists reside in the (R)-enantiomer, with the (S)-enantiomer being virtually inactive. In recent years the suspicion has been raised that the (S)-enantiomer of the beta2-agonists is responsible for induction of airway hyperreactivity. This suspicion is based primarily on results obtained in guinea pigs exposed to (S)-enantiomers of beta2-agonists. A number of experiments in vitro have been undertaken to find a mechanism of action for these observations in vivo. Most of the results obtained are equivocal. However, the observation that (S)-salbutamol may cause mobilization of intracellular Ca2+, apparently by means of a cholinergic mechanism, deserves further investigation. The clinical studies are focused on the enantiomers of salbutamol. They confirm the preclinical findings that the pulmonary, as well as the extrapulmonary, effects of salbutamol reside in the (R)-enantiomer. The studies available so far do not convincingly show clinically significant airway hyperreactivity after exposure to the (S)-enantiomer. Further studies are needed to settle this issue.

Newer therapeutic agents for asthma

The past decade has seen significant advances in the available treatments for asthma. These include longer-acting bronchodilating agents, high topical potency inhaled corticosteroids, and agents that interfere with leukotriene production or action. Table 3 summarizes the clinical effects of the newer therapeutic agents reviewed. Experimental therapies for the steroid-dependent patient have also been discussed. Although clinical trials to date have established many of these as effective in asthma, the results of ongoing, large, multicenter studies investigating the relative merits of these therapies, alone and in combination, will further clarify how to maximize the utility of these agents in the treatment of asthma.

Long-term cardiovascular safety of salmeterol powder pharmacotherapy in adolescent and adult patients with chronic persistent asthma: a randomized clinical trial

STUDY OBJECTIVES

This study investigates the long-term cardiovascular safety of salmeterol powder vs placebo in adolescent and adult patients with mild persistent asthma.

DESIGN

Multicenter, randomized, double-blind, placebo-controlled, parallel-group study.

SETTING

Eighteen US clinical centers.

PATIENTS

Three hundred fifty-two patients (> or = 12 years) with mild persistent asthma (duration > or = 6 months) requiring pharmacotherapy; with FEV1 of 70 to 90% of predicted and without abnormal ECG/continuous ambulatory ECG (Holter).

INTERVENTIONS

Randomized to twice-daily salmeterol powder (50 microg) or placebo via breath-actuated device for 52 weeks. Backup albuterol was available to control asthma symptoms.

MEASUREMENTS AND RESULTS

Cardiovascular safety was regularly assessed by 12-lead ECG with a 15-s lead II rhythm strip, 24-h continuous ambulatory ECG (Holter) monitoring, serial vital sign measurements, and review of adverse cardiovascular events. No deaths occurred during the study. No clinically significant between-group differences were observed in pulse rate, ECG QTc interval, median number of ventricular or supraventricular ectopic events, incidence of ventricular ectopic couplets and runs, or incidence of > 100 ventricular or supraventricular ectopic events in 24 h. No clinically significant between-group differences were observed in arterial BP or incidence of adverse cardiovascular events. Salmeterol was well tolerated throughout the 52-week study period, with a cardiovascular safety profile similar to that of placebo.

CONCLUSIONS

Long-term, twice-daily pharmacotherapy with salmeterol powder is safe and is not associated with unfavorable clinically significant changes in cardiac function or increases in cardiovascular adverse effects.

Cardiac side effects of long-acting beta-2 agonist salmeterol in asthmatic children

BACKGROUND

Salmeterol is a new long-acting beta 2 selective adrenoreceptor agonist. There are some reports about the cardiac side-effects of salmeterol in asthmatic adults. The aim of this study was to determine the cardiac side effects of salmeterol in children.

METHODS

Seventeen children with moderate asthma (aged between 6 and 13 years, mean 8.76 years) received salmeterol with a spacer device (Volumatic 200 micrograms daily, b.i.d.) for 3 weeks. All the children were evaluated by 24 h ambulatory electrocardiography monitoring and echocardiography before, on the second and on the 21st day of treatment.

RESULTS

In minimum heart rate measurements, there were significant differences between the baseline (mean +/- SD 54.29 +/- 7.13), second (59.24 +/- 6.86) and 21st day (60.65 +/- 8.23) results. Also, the mean heart rate before the treatment (89.59 +/- 6.78) was significantly different from that on the second (94.76 +/- 6.51) and 21st day (92.65 +/- 8.90) of treatment. Although all the values were within normal limits and there were no significant differences between the control group's values, a trend of increase in mean and the minimum heart rates was seen. There were no significant differences in blood pressure, serum K+, maximum heart rate, supraventricular and ventricular ectopic beats, ejection fraction, stroke volume, cardiac output and corrected QT interval at any time. No complaints of tremors or palpitations were reported.

CONCLUSIONS

As no cardiac side effects were detected, it could be concluded that salmeterol is quite a safe drug for use in childhood asthma treatment.

Recent developments in respiratory care pharmacology

Bronchoactive inhaled aerosol drugs target the respiratory tract directly and seek to minimize systemic exposure and reduce side effects. Common delivery devices such as the metered dose inhaler, the small volume nebulizer, or the dry powder inhaler each deliver approximately the same fraction of dose (10%) to the lungs, although their dose amounts are not equivalent. Major respiratory drug groups are reviewed, and include the beta-adrenergic and anticholinergic bronchodilators, mucolytic agents, corticosteroids, mediator antagonists, anti-infective agents, and exogenous surfactants. New agents in each group are identified and briefly described, along with the clinical use and most commonly observed side effects for each class of drugs.

The beta-adrenoceptor

The human beta-adrenoceptor is a member of the seven-transmembrane family of receptors, encoded by a gene on chromosome 5. beta-Adrenoceptors have been classified into beta1, beta2, and beta3 subgroups, with beta2-receptors being widely distributed in the respiratory tract, particularly in airway smooth muscle. Intracellular signaling following beta2-adrenoceptor activation is largely affected through a trimeric Gs protein coupled to adenylate cyclase. Cyclic AMP (cAMP) induces airway relaxation through phosphorylation of muscle regulatory proteins and attenuation of cellular Ca2+ concentrations. Alternative cAMP-independent pathways involving activation of membrane maxi-K+ channels and coupling through Gi to the MAP kinase system have also been described. Site-directed mutagenesis has identified Asp 113 and Ser 204/207 within the third and fourth membrane domains as the active site of the beta2-receptor, critical for beta2-agonist binding and activity. beta2-Agonists have been characterized as those that directly activate the receptor (albuterol), those that are taken up into a membrane depot (formoterol), and those that interact with a receptor-specific auxiliary binding site (salmeterol). These differences in mechanism of action are reflected in the kinetics of airway smooth muscle relaxation and bronchodilation in patients with asthma. beta-Adrenoceptor desensitization associated with beta2-agonist activation is a consequence of phosphorylation by beta-ARK and uncoupling of the receptor from Gs following beta-arrestin binding, of internalization and recycling of the receptor through processes of sequestration and resensitization and downregulation, modulated by an effect on receptor gene expression. The degree of receptor desensitization appears to differ, depending on the cell or tissue type, and is reflected in the different profiles of clinical tolerance to chronic beta2-agonist therapy. A number of polymorphisms of the beta2-receptor have been described that appear to alter the behavior of the receptor following agonist exposure. These include Arg-Gly 16, Glu-Gln 27, and Thr-lle 164. The Gly 16 receptor downregulates to a greater extent and is associated with increased airway hyperreactivity, nocturnal symptoms, and more severe asthma. The Glu 27 form appears to protect against downregulation and is associated with less reactive airways. An individual can be homozygous or heterozygous for given polymorphisms, and large populations will have to be studied to determine their importance to the asthma phenotype.

Short-term cardiovascular effects of salmeterol

The occurrence of cardiovascular side effects is sometimes associated with the utilization of beta-adrenoceptor agonists. The most important causes of these undesirable pharmacologic actions are as follows: (1) direct stimulation of cardiac beta-adrenoceptors; (2) reflex activation of adrenergic mechanisms due to peripheral vasodilation; (3) hypokalemia; and (4) hypoxemia. The aim of this study was to evaluate the potential short-term, cardiovascular side effects of salmeterol, a long-acting and highly selective beta2-adrenoceptor agonist. Eight volunteer healthy subjects and eight patients with reversible airway obstruction and without cardiovascular alterations were treated with 50 microg of salmeterol twice a day for 3 days and then with 100 microg of salmeterol twice a day for a further 3-day period. The 24-h ECG (Holter) monitoring and measurement of arterial BP, performed on the admission day and on the third and the sixth day of pharmacologic treatment, showed that salmeterol did not produce any significant change in mean heart rate, number of supraventricular and ventricular premature complexes, and BP. Furthermore, no ECG abnormality related to myocardial ischemia was recorded during 24-h Holter monitoring. These data suggest that salmeterol, administered in regular and high doses for a short period, does not cause significant cardiovascular effects in both normal subjects and patients with reversible airway obstruction.

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.

(S)-Albuterol increases intracellular free calcium by muscarinic receptor activation and a phospholipase C-dependent mechanism in airway smooth muscle

Racemic albuterol has been one of the most widely used beta2-adrenoceptor agonists for the relief of the symptoms of asthma, yet the use of beta2 agonists has been known to induce bronchial hyperresponsiveness. To probe a possible role of the S-enantiomer for hyperresponsiveness, we determined the effects of (S)-albuterol on intracellular Ca2+ concentration ([Ca2+]i) in dissociated bovine tracheal smooth muscle cells. Both (S)-and (R,S)-albuterol increased [Ca2+]i at concentrations of >10 pM and 1 nM, respectively, with a maximal response by 150 and 100 nM, respectively. (S)-Albuterol (1 and 10 muM) induced Ca2+ oscillations, reaching 1-2 muM [Ca2+]i. This response is in a stark contrast to that of (R)-albuterol, which decreased [Ca2+]i. The increase in [Ca2+]i was blocked by 100 nM atropine or 500 nM 4-diphenylacetoxy-N-methylpiperidine but was insensitive to the beta2 antagonist ICI 118,551 (10 muM). (S)-Albuterol (10 muM) increased inositol-1,4,5-trisphosphate levels by 213 +/- 34.4% (p < 0.05, four experiments) in cells exposed for 30 sec. The sustained phase of the Ca2+ increase was absent in Ca2+-free solution, suggesting that Ca2+ influx was responsible for the sustained Ca2+ response. The results also suggest that (S)-albuterol may cross-react with muscarinic receptors. As a Ca2+ agonist in airway smooth muscle, (S)-albuterol may have profound clinical implications because 50% of prescribed racemic albuterol is composed of (S)-albuterol.

Salmeterol inhibition of mediator release from human lung mast cells by beta-adrenoceptor-dependent and independent mechanisms

1. The long-acting beta2-adrenoceptor agonist, salmeterol (10(-9)-10(-5) M), inhibited the IgE-mediated release of histamine from human lung mast cells (HLMC) in a dose-dependent fashion. Additional beta-adrenoceptor agonists were studied and the rank order of potency for the inhibition of histamine release from HLMC was isoprenaline > salmeterol > salbutamol. Approximate EC50 values for the inhibition of histamine release were 10 nM for isoprenaline and 100 nM for salbutamol. An EC50 value for salmeterol could not be calculated because maximal responses to salmeterol were not observed over the concentration range employed. 2. Both salmeterol and isoprenaline inhibited the generation of sulphopeptidoleukotrienes (sLT) more potently and more efficaciously than the release of histamine from immunologically-activated HLMC. Salmeterol (EC50 < 0.1 nM) was more potent than isoprenaline (EC50 0.4 nM) at attenuating sLT generation. 3. The beta-adrenoceptor antagonist, propranolol (1 microM), and the selective beta2-adrenoceptor antagonist, ICI 118,551 (0.1 microM), both caused rightward shifts in the dose-response curve for the inhibition of histamine release by isoprenaline. The antagonism of salmeterol effects by propranolol and ICI 118,551 was more complex. At lower concentrations (< 1 microM) of salmeterol, both antagonists shifted the dose-reponse curve to salmeterol rightward. At a higher concentration (10 microM) of salmeterol, neither ICI 118,551 nor propranolol was an effective antagonist of the salmeterol-mediated inhibition of histamine release. 4. Prolonged exposure (4 h) of HLMC to isoprenaline (1 microM) caused an approximately 50% reduction in the effectiveness of a second exposure to isoprenaline (10 microM) at inhibiting the release of histamine. whereas this pretreatment did not affect the salmeterol (10 microM) inhibition of histamine release. 5. Isoprenaline (10(-9)-10(-5) M) caused a dose-dependent increase in total cell cyclicAMP levels in purified HLMC which paralleled the inhibition of histamine release. Salmeterol (10(-9)-10(-5) M) was considerably less potent than isoprenaline at increasing HLMC cyclicAMP levels. 6. In summary, these data indicate that salmeterol is an effective inhibitor of the stimulated release of mediators from HLMC. The present data also suggest that salmeterol may act to inhibit mediator release from HLMC by beta-adrenoceptor-dependent and independent mechanisms.

Salmeterol-induced desensitization, internalization and phosphorylation of the human beta2-adrenoceptor

1. Partial agonists of the beta2-adrenoceptor which activate adenylyl cyclase are widely used as bronchodilators for the relief of bronchoconstriction accompanying many disease conditions, including bronchial asthma. The bronchodilator salmeterol has both a prolonged duration of action in bronchial tissue and the ability to reassert this activity following the temporary blockade of human beta2-adrenoceptors with antagonist. 2. We have compared the activation and desensitization of human beta2-adrenoceptor stimulation of adenylyl cyclase induced by salmeterol, adrenaline and salbutamol in a human lung epithelial line, BEAS-2B, expressing beta2-adrenoceptor levels of 40-70 fmol mg(-1), and in human embryonic kidney (HEK) 293 cell lines expressing 2-10 pmol mg(-1). The efficacy observed for the stimulation of adenylyl cyclase by salmeterol was only approximately 10% of that observed for adrenaline in BEAS-2B cells expressing low levels of beta2-adrenoceptor, but similar to adrenaline in HEK 293 cells expressing very high levels of receptors. Salmeterol pretreatment of these cells induced a rapid and stable activation of adenylyl cyclase activity which resisted extensive washing and beta2-adrenoceptor antagonist blockade, consistent with binding to a receptor exosite and/or to partitioning into membrane lipid. 3. The desensitization and internalization of beta2-adrenoceptors induced by the partial agonists salmeterol and salbutamol were considerably reduced relative to the action of adrenaline. Consistent with these observations, the initial rate of phosphorylation of the receptor induced by salmeterol and salbutamol was much reduced in comparison to adrenaline. 4. Our data suggest that the reduction in the rapid phase of desensitization of beta2-adrenoceptors after treatment with salmeterol or salbutamol is caused by a decrease in the rate of beta2-adrenoceptor kinase (betaARK) phosphorylation and internalization. In contrast, the rate of cyclic AMP-dependent protein kinase (PKA)-mediated phosphorylation by these partial agonists appears to be similar to adrenaline.

Dose equivalence and bronchoprotective effects of salmeterol and salbutamol in asthma

BACKGROUND

Salbutamol is the most widely prescribed short acting beta 2 agonist and salmeterol is the first long acting inhaled beta 2 agonist. The dose equivalence of salmeterol and salbutamol is disputed. Estimates of weight-for-weight dose ratio have ranged from 1:2 to 1:16. A study was undertaken to clarify the true dose ratio.

METHODS

The bronchoprotection afforded against repeated methacholine challenge by inhaled salmeterol 25 micrograms and 100 micrograms and salbutamol 100 micrograms and 400 micrograms was compared in a randomised, double blind, placebo controlled, crossover trial. Subjects were 16 stable asthmatics with a baseline forced expiratory volume in one second (FEV1) of > or = 65% predicted, screening concentration provoking a fall in FEV1 of 20% (PC20FEV1) of < or = 8mg/ml, and a shift in PC20FEV1 of more than two doubling concentration steps following inhalation of salbutamol 400 micrograms. On five separate occasions subjects underwent methacholine challenge before and 30 and 120 minutes after drug administration. PD20FEV1 was calculated for each challenge. FEV1 at 90 minutes after drug administration was also recorded.

RESULTS

Bronchoprotection afforded by salmeterol was increased at 120 minutes compared with 30 minutes and protection by salbutamol was decreased. Protection by both doses of salmeterol was similar to salbutamol 100 micrograms at 30 minutes but significantly greater at 120 minutes. FEV1 at 90 minutes was significantly greater after salmeterol 100 micrograms than after placebo, but there were no other significant differences between treatments. Maximal observed protection was equivalent for salmeterol 100 micrograms and salbutamol 400 micrograms.

CONCLUSIONS

The data are compatible with a weight-for-weight dose ratio for salmeterol:salbutamol of < or = 1:4.

Differential contribution of two serine residues of wild type and constitutively active beta2-adrenoceptors to the interaction with beta2-selective agonists

1. We have studied the difference in receptor binding activity between partial and full beta2-adrenoceptor agonists and the abilities of the agonists to interact with Ser204 and Ser207 in the fifth transmembrane region of the beta2-adrenoceptor, amino acid residues that are important for activation of the beta2-adrenoceptor. 2. In the binding study with [125I]-iodocyanopindolol, the Ki values of (+/-)-salbutamol, (+/-)-salmeterol, TA-2005 and (-)-isoprenaline for the beta2-adrenoceptor expressed in COS-7 cell membranes were 3340, 21.0, 12.0 and 904 nM, respectively. The beta1/beta2 selectivity of these agonists was in the order of (+/-)-salmeterol (332 fold) > TA-2005 (52.8) > (+/-)-salbutamol (6.8) > (-)-isoprenaline (1.1), and the beta3-/beta2-adrenoceptor selectivity of these agonists was in the order of TA-2005 (150 fold) > (+/-)-salmeterol (88.6) > (+/-)-salbutamol (10.4) > (-)-isoprenaline (3.2). 3. The maximal activation of adenylyl cyclase by stimulation of the beta1-, beta2- and beta3-adrenoceptors by TA-2005 was 32, 100 and 100% of that by (-)-isoprenaline, respectively, indicating that TA-2005 is a full agonist at the beta2- and beta3-adrenoceptors and a partial agonist at the beta1-adrenoceptor. (+/-)-Salbutamol and (+/-)-salmeterol were partial agonists at both beta1- (8% and 9% of (-)-isoprenaline) and beta2- (83% and 74% of (-)-isoprenaline) adrenoceptors. 4. The affinities of full agonists, TA-2005 and (-)-isoprenaline, were markedly decreased by substitution of Ala for Ser204 (S204A) of the beta2-adrenoceptor, whereas this substitution slightly reduced the affinities of partial agonists, (+/-)-salbutamol and (+/-)-salmeterol. Although the affinities of full agonists for the S207A-beta2-adrenoceptor were decreased, those of partial agonists for the S207A-beta2-adrenoceptor were essentially the same as for the wild type receptor. 5. The constitutively active mutant (L266S, L272A) of the beta2-adrenoceptor had an increased affinity for all four agonists. The affinities of full agonists were decreased by substitution of Ser204 of the constitutively active mutant, whereas the degree of decrease was smaller than that caused by the substitution of the wild type receptor. Although the affinities of (+/-)-salbutamol and (+/-)-salmeterol for the S207A-beta2-adrenoceptor were essentially the same as those for the wild type beta2-adrenoceptor, the affinities of (+/-)-salbutamol and (+/-)-salmeterol for the constitutively active beta2-adrenoceptor were decreased by substitution of Ser207. 6. These results suggest that Ser204 and Ser207 of the wild type and constitutively active beta2-adrenoceptors differentially interacted with beta2-selective agonists.

The duration of action of non-beta 2-adrenoceptor mediated responses to salmeterol

1. To investigate further the mechanism of the long duration of action of the selective beta 2-adrenoceptor agonist, salmeterol, we have determined the duration of action of some responses to salmeterol which are not mediated through beta 2-adrenoceptors. 2. In the presence of propranolol (1 microM), salmeterol (1-30 microM) caused concentration-related relaxation of superfused, pre-contracted strips of guinea-pig gastric fundus. On washing the tissues, these relaxant responses were rapidly lost, the time to 50% recovery being approximately 30 min. 3. In human neutrophils, salmeterol (1-100 microM) caused concentration-related inhibition of FMLP-induced O2- release. Propranolol (1 microM) had little or no effect on the inhibitory activity of salmeterol. Washing the cells twice over a 40 min period caused a marked reduction of the inhibitory activity of salmeterol. 4. In guinea-pig superfused trachea, in the absence of propranolol, infusions of (RS)-salmeterol (10-30 nM) and the less potent (S)-enantiomer of salmeterol (300-3000 nM) inhibited electrically-induced contractile responses. When the infusion was stopped, there was no recovery from the inhibitory responses within 200 min. In the presence of propranolol (1 microM), infusions of (RS)-salmeterol (10 microM) and (S)-salmeterol (10-100 microM) also inhibited the contractile responses, but, in contrast, on stopping the infusions differences were observed in recovery times. Thus no appreciable recovery was observed from the responses to (RS)-salmeterol, whereas a rapid loss of inhibition was observed on stopping the infusion of (S)-salmeterol, the time to 50% recovery being 30-35 min. 5. These relatively short-lasting effects of salmeterol which are not mediated through beta 2-adrenoceptors, contrast with the persistence of the responses which are mediated through beta 2-adrenoceptors seen in a variety of tissues, but are similar to the rate of dissociation of salmeterol observed from artificial membranes. These observations suggest that the sustained agonist activity of salmeterol is peculiar to responses mediated by beta 2-adrenoceptors.

Characterization of beta-adrenergic receptors of freshly isolated astrocytes and neurons from rat brain

The binding and characteristics of rat brain beta-adrenergic receptors (beta-AR) isolated from astrocytes and neurons were investigated. Equilibrium binding experiments demonstrated that beta-AR were more concentrated on astrocytes than on neurons isolated from forebrain, cerebral cortex and cerebellum. Inhibition experiments revealed that beta 1-AR and beta 2-AR were present in the two cell types. Isoproterenol revealed two interchangeable states of high and low affinity binding to both beta 1- and beta 2-AR in neurons. The high affinity binding sites were sensitive to guanylylimidodiphosphate (GppNHp). Similar results were found with other beta-AR agonists but not with salbutamol and salmeterol which recognized both affinity states of the neuronal beta 2-AR but only the low affinity state of beta 1-AR. In astrocytes only the low affinity state of beta-AR was observed.

Effects of salmeterol and terbutaline on IgE-mediated dermal reactions and inflammatory events in skin chambers in atopic patients

The objective of the present study was to investigate the potential of the long-acting beta 2-agonist salmeterol as an inhibitor of various components of IgE-mediated inflammatory in man. For this purpose, we measured gross skin reactivity (diameters of wheal and flare reaction [WFR] and late cutaneous reaction [LCR] as well as inflammatory cells, mediators, and protein in cutaneous suction blister chambers in eight subjects with allergic rhinitis. Blisters were induced, two on each forearm, by gentle suction and heating, and were unroofed 12 h later, after which plastic chambers were placed over the denuded area. The chambers were challenged for 2 h with antihuman IgE (titer 1:10) in the presence and absence of salmeterol or terbutaline. Normal goat IgG served as negative control. Chamber fluids were removed hourly for the first 4 h, and this followed by a 4-h incubation before final collection. Salmeterol (10(-6)M) and terbutaline (10(-5)M) injected intradermally 30 min before, aw well as together with anti-IgE (titer 1:100), inhibited the WFRs by up to 30%. The effect of salmeterol on the ensuing LCR (75% inhibition at 24 h) tended to be more pronounced than the corresponding inhibition by terbutaline. Both salmeterol and terbutaline very effectively inhibited the anti-IgE-induced extravasation of alpha 2-macroglobulin into skin chambers, with a significantly more sustained effect by salmeterol. Interestingly, only terbutaline reduced the histamine release evoked by anti-IgE. With the present experimental design, where both drugs were washed out from the chambers after 2 h, neither drug inhibited recruitment of leukocytes (including eosinophils). Taken together, salmeterol had a more sustained inhibitory effect than terbutaline on indices of IgE-mediated edema formation (late induration and plasma protein extravasation). On the other hand, under the present experimental conditions, salmeterol failed to reduce the histamine release (in contrast to terbutaline), and neither salmeterol nor terbutaline affected the recruitment of leukocytes.

Physiological perspectives of therapy in bronchial hyperreactivity

PURPOSE

This paper reviews the literature on the aetiology and therapy of bronchial hyperreactivity to describe the underlying pathophysiology, identify patients at risk and update knowledge on new and existing therapies.

SOURCE

Information was obtained from monograms on New Drugs for Asthma, Respiratory Medicine: recent advances, Agents and Actions Supplements, Pulmonary Pharmacology, Anesth Analg, the European Journal of Respiration and a Medline literature search.

PRINCIPAL FINDINGS

Reduced airway calibre, increased bronchial contractility, altered permeability of the bronchial mucosa, humoral and cellular mediators, and dysfunctional neural regulation are critical factors for bronchial hyperreactivity, a characteristic feature of hyperreactive airways which results in bronchoconstriction after exposure to varied stimuli. Preoperative anaesthetic considerations in these patients include FEV1 and PEFR testing to assess the severity and for optimal control of the condition. Bronchospasm causing hypoxaemia is the major intraoperative problem anticipated in these patients. Current therapeutic management of bronchoconstriction focuses on the beta 2 agonists, theophylline and steroids. Besides relaxing the airway smooth muscle these agents are all capable of altering bronchial inflammatory responses. Future developments of therapy are directed towards the inflammatory components of the disease.

CONCLUSION

This review has presented background information on physiological mechanisms of smooth muscle contractility, pathophysiological alterations of bronchial contractility and the pharmacological basis of therapy in bronchoconstrictive disease. Information is presented to enable the prompt arrest and reversal of airway constriction, and to maintain prophylactic treatment during the perioperative period. Intraoperative bronchospasm is managed by adequate oxygenation and reversal of bronchoconstriction.

Some pharmacodynamic aspects on long-acting beta-adrenoceptor agonists

1. Formoterol and salmeterol are the first members of a new generation of long-acting beta(2)-adrenoceptor agonists for inhalation. The discovery of the long effect duration of formoterol was made by chance, while the development of salmeterol appeared to follow a purposeful research strategy. 2. Preclinical evaluation predictive of the clinical duration of effect of long-acting bronchodilators is not straightforward. Experiments in vitro may give false positive results, while experiments in vivo may show false negative results. 3. Once the principle of a long duration of effect was established, a number of novel long-acting beta(2)-adrenoceptor agonists of various chemical structure have emerged. 4. There are two alternative models for the explanation of the long duration of effect: the exosite binding explaining the mode of action of salmeterol, and the more general diffusion microkinetic model applicable for both formoterol and salmeterol. 5. Long-acting beta-adrenoceptor agonists with a relatively low efficacy like salmeterol may, under certain circumstances, inhibit competitively the relaxing effect of agonists with higher efficacy like formoterol and salbutamol. 6. Like all other beta(2)-adrenoceptor agonists in current clinical use, formoterol and salmeterol comprise racemic mixtures. Only the RR- and R-enantiomers are pharmacologically active. The experimental compounds TA-2005 and picumeterol have been developed as pure RR- and R-enantiomers, respectively.

Ex vivo pharmacologic modulation of basophil histamine release in asthmatic patients

Histamine is one of a range of mediators which play an important role in asthma, and the "releasability" of basophils has been shown to be upregulated in this disease. In vitro, beta 2-agonists and to a lesser extent corticosteroids have been shown to reduce histamine release. The ex vivo effects of salmeterol and inhaled corticosteroids on histamine release were studied in 78 asthmatic patients with variable disease severity and 20 control subjects. Spontaneous and anti-IgE-induced histamine release was measured in all subjects. Fifteen patients were not receiving any form of treatment, 42 were treated with inhaled corticosteroids, and 21 received inhaled corticosteroids and salmeterol. Seven patients treated with inhaled corticosteroids and seven patients treated with inhaled corticosteroids and salmeterol were tested twice to assess the effect of salmeterol on histamine release. Nine patients treated with inhaled corticosteroids were tested before and after 1 month of salmeterol treatment to determine the possible inhibition by salmeterol. Patients who were treated with inhaled corticosteroids and salmeterol showed significantly lower levels of spontaneous histamine release (median: 2.5%) than untreated (5.2%) and inhaled corticosteroids-treated asthmatics (3.4%). No tachyphylaxis to salmeterol was observed when patients were tested twice at a 3-month interval. This study suggests that salmeterol may have an additive anti-inflammatory effect with inhaled corticosteroids, although this hypothesis must be tested by further studies involving cells obtained by bronchoalveolar lavage and studies with bronchial biopsies.

Isoetharine versus albuterol for acute asthma: greater immediate effect, but more side effects

PURPOSE

To compare the magnitudes of the immediate effects of the nebulized beta-agonists isoetharine and albuterol in the treatment of acute severe asthma.

PATIENTS AND METHODS

Fifty-one adults presenting with severe asthma exacerbations (forced expiratory volumes in the first second of exhalation [FEV1] <40% of predicted) to the emergency department were randomized (double-blind) to receive hourly inhaled nebulization treatment with either isoetharine (5 mg) or albuterol (2.5 mg). The FEV1 was measured immediately before and after each nebulized treatment. Any side effects were recorded.

RESULTS

Immediately after the first nebulized treatment, the isoetharine group improved its mean FEV1 (+/-SEM) by a significantly greater amount than did the albuterol group: 60% +/- 11% versus 39% +/- 5%, respectively (P <0.05). One hour later the mean FEV1 were equivalent. This pattern repeated itself after the second hourly treatment. The two groups did not differ in any outcome parameters (FEV1 at discharge, number of nebulized treatments required, the number of inpatient admissions, number of clinical relapses after discharge). More patients treated with isoetharine had side effects (36% versus 4% for albuterol, P <0.01), 1 of whom required discontinuation from the study.

CONCLUSIONS

Both medications were equally effective in alleviating bronchospasm. The immediate effect of isoetharine was significantly greater, but equalized that of albuterol within an hour after treatment. There were more side effects with isoetharine.

Comparison of the effects of salmeterol and salbutamol on clinical activity and eosinophil cationic protein serum levels during the pollen season in atopic asthmatics

BACKGROUND

In atopic asthma there is strong evidence of eosinophils playing an active role in pathogenesis. Some investigations demonstrated that eosinophil cationic protein (ECP) serum levels increased in atopic patients with asthma during pollen season.

OBJECTIVE

The aim of the study was to evaluate the effects of short-term (1 week) beta 2-agonist treatment on lung function and eosinophil activity in asthmatic patients.

METHODS

We used an open, randomized, cross-over design to compare the effects of salbutamol (200 micrograms q.i.d.) and salmeterol (50 micrograms b.i.d.) on peak expiratory flow rate (PEFR), blood eosinophil count and serum levels of ECP as a measure of eosinophil activity in 20 mild atopic asthmatics.

RESULTS

Morning and evening PEFR values were both significantly higher during salmeterol treatment than during the salbutamol period. Conversely, both morning and evening daily asthma symptom scores were significantly lower during salmeterol treatment compared with those recorded during the salbutamol period. The mean basal eosinophil blood count on salmeterol treatment (601 +/- 189 mm3) was not higher than the mean count on salbutamol treatment (612 +/- 204 mm3). After both treatments the mean eosinophil blood counts were unchanged (619 +/- 189 mm3 and 576 +/- 212 mm3, respectively). No significant differences in blood eosinophil counts were observed between or within treatments at any time. No significant difference was observed in baseline mean ECP serum concentration (43.8 +/- 26.3 micrograms/L on salmeterol treatment and 41.7 +/- 29.8 micrograms/L on salbutamol treatment, respectively). After salmeterol treatment the mean ECP serum concentration had fallen significantly to 20.9 +/- 18.6 micrograms/L (P < 0.01), whereas after salbutamol treatment it was unchanged (42.0 +/- 25.1 micrograms/L). Salmeterol treatment produced a decrease in ECP serum levels without any changes in blood eosinophil count.

CONCLUSION

This study demonstrates that salmeterol affords a significant improvement in asthma control during the pollen season, measured by both subjective and objective parameters, compared with salbutamol. This greater efficacy may be related to inhibition of eosinophil degranulation during the pollen season.

Pharmacological characteristics and species-related variations of beta 3-adrenergic receptors

Beta-adrenergic receptors (beta-AR) belong to the large multigenic family of receptors coupled to GTP-binding proteins. Three subtypes have been identified: beta 1-, beta 2- and beta 3-AR. Much of the work delineating the precise pharmacological comparison of the three beta-ARs has come from investigations with stably transfected Chinese hamster ovary cells (CHO cells). This review discusses the structure and function of beta 3-AR in various species and presents new findings on a number of beta 3-AR ligands including carazolol, tertatolol and CL 316,243 which were found to be selective and potent beta 3-AR agonists and ZD 2079 and salmeterol which appear to display full but non-subtype selective agonistic activity. Species-related variations of the beta 3-AR pharmacology have been shown for propranolol and bupranolol. With the ongoing characterization of the beta 3-AR at the molecular and cellular level, and with the advent of computer-assisted molecular modelling to aid in the determination of the three-dimensional structure of the receptor, it is thought that novel beta 3-AR compounds will become available with improved selectivity and potency.

Abecarnil enhances GABA-induced currents in acutely isolated cerebellar Purkinje cells

The effect of abecarnil, a beta-carboline derivative acting at central gamma-aminobutyric acid (GABAA)/benzodiazepine receptors, on the response to GABA of isolated Purkinje cells acutely dissociated from rat cerebellar slices was studied. Using a rapid superfusion system to apply drugs and whole-cell voltage-clamp recording configuration, abecarnil was found to be of similar efficacy to diazepam (DZP) in enhancing GABA-mediated responses. Abecarnil potentiated GABA-induced chloride currents maximally by 241%, while DZP showed a maximal potentiation of 217%. However, abecarnil was more potent than DZP and exhibited different potentiation kinetics. While the response to DZP was fast and reversible, abecarnil after a 1-3 sec application initially produced only a very small enhancement of the GABA response. The effect then developed gradually even after cessation of abecarnil application, and depended on both abecarnil concentration and exposure time. It is suggested that abecarnil accumulates in the lipid membrane resulting in slow effect kinetics and prolonged presence at the benzodiazepine binding site. Abecarnil is a full agonist at the GABAA/benzodiazepine receptor on Purkinje cell somatic membranes.

The interaction between salmeterol and beta 2-adrenoceptor agonists with higher efficacy on guinea-pig trachea and human bronchus in vitro

1. In guinea-pig tracheal preparations precontracted with 1 mumol l-1 carbachol, formoterol, procaterol, fenoterol, salmefamol, salbutamol and terbutaline (in that order of potency) caused a concentration-dependent and almost complete, relaxation. However, under these conditions, the maximum relaxation by salmeterol was approximately 30% of the maximum attainable relaxation. 2. We have therefore explored the ability of salmeterol to inhibit the relaxant response to beta 2-adrenoceptor agonists of different chemical structure and relatively higher efficacy in smooth muscle preparations from guinea-pig trachea and human bronchus. 3. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curves for the other agonists were shifted to the right in a variable way by 1.8-2.8 log units, fenoterol and salbutamol being the extremes. 4. When 20 mumol l-1 sulfonterol, another low efficacy beta 2-adrenoceptor agonist, was substituted for salmeterol, the difference in the magnitude of the rightward shift between fenoterol and salbutamol was eliminated. 5. In the human bronchus, formoterol and terbutaline had a higher apparent efficacy than salmeterol. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curve for formoterol was shifted 2.7 log units to the right. 6. Salmeterol inhibits, competitively, relaxant responses to beta 2-adrenoceptor agonists with higher efficacy. The degree of inhibition seems to be dependent on the agonist used. This contrasts with results obtained with sulfonterol and suggests that salmeterol interacts with the beta 2-adrenoceptor in a complex way.

Formoterol on airway smooth muscle and human lung mast cells: a comparison with salbutamol and salmeterol

Formoterol, like salbutamol and salmeterol, relaxed isolated preparations of guinea-pig trachea and human bronchus, and inhibited antigen-induced mediator release from human lung fragments in a concentration-related fashion. In each case, these actions were mediated through beta 2-adrenoceptors, with formoterol being 50-120-fold more potent than salbutamol, and 2-27-fold more potent than salmeterol. The duration of action of formoterol was longer than that of salbutamol in all preparations, but was markedly shorter than that of salmeterol, whose actions persisted for many hours despite continuous or extensive washing of the tissues. In conscious guinea-pigs, inhaled formoterol, salbutamol and salmeterol all caused dose-related inhibition of histamine-induced bronchoconstriction. Formoterol was again more potent (10-20-fold) than either salbutamol or salmeterol. However, while the actions of a threshold-effective dose of formoterol persisted for less than 3 h, somewhat longer than those of salbutamol (< 1.5 h), an equivalent dose of salmeterol was active for at least 6 h. Therefore, while formoterol is a potent beta 2-adrenoceptor agonist in vitro and in vivo, and is consistently longer-acting than salbutamol, its duration of action is markedly shorter than that of salmeterol.

Comparison of the anti-inflammatory properties of formoterol, salbutamol and salmeterol in guinea-pig skin and lung

1. We have compared some anti-inflammatory properties of formoterol, salbutamol and salmeterol in guinea-pig skin and lung. 2. Intradermal formoterol (1 x 10(-10) to 1 x 10(-8) mol/site), salbutamol (1 x 10(-8) and 1 x 10(-7) mol/site) and salmeterol (1 x 10(-8) and 1 x 10(-7) mol/site) inhibited bradykinin-induced plasma protein extravasation (PPE) in guinea-pig skin. A maximally effective dose of formoterol (1 x 10(-9) mol/site) and salbutamol (1 x 10(-8) mol/site) inhibited PPE in guinea-pig skin for 2-4 h and 1-2 h respectively, whereas salmeterol (1 x 10(-8) mol/site) was effective for > 6 h. 3. Inhaled formoterol (nebuliser concentration 0.1 to 100 micrograms ml-1 inhibited histamine-induced plasma protein extravasation (PPE) in guinea-pig lung, with significant inhibition being observed at 10 and 100 micrograms ml-1. Formoterol (100 micrograms ml-1) inhibited PPE in guinea-pig lung for 2-4 h, a duration of action intermediate between that previously obtained for salbutamol (1 h) and salmeterol (> 6 h). 4. Formoterol, like salbutamol, had no effect on neutrophil accumulation or granulocyte-dependent PPE (zymosan-induced) in guinea-pig skin. Formoterol inhibited neutrophil accumulation (lipopolysaccharide-induced) in guinea-pig lung but at doses greater than those required to inhibit granulocyte-independent PPE (histamine-induced). In contrast, salmeterol inhibited neutrophil accumulation and granulocyte-dependent PPE in guinea-pig skin and inhibited neutrophil accumulation in guinea-pig lung at doses which inhibit granulocyte-independent PPE. 5. Inhaled formoterol (nebuliser concentration 100 microg ml-1) and salmeterol (100 microg ml-1) both inhibited PAF-induced eosinophil accumulation in guinea-pig lung. However, unlike salmeterol, this effect of formoterol was observed only at suprabronchodilator doses.6. We conclude that to inhibit neutrophil accumulation, at doses which inhibit granulocyte-independent PPE, agonists acting at beta-adrenoceptors on vascular endothelium require a duration of action greater than that of salbutamol and formoterol. However, we speculate that the mechanism of inhibition of eosinophil accumulation in guinea-pig lung by beta2-adrenoceptor agonists may involve an action on beta2-adrenoceptors on a cell type other than the endothelial cell.