Effect on airway responsiveness of six weeks treatment with salmeterol

It has been suggested that the new long-acting beta 2-agonist, salmeterol, has anti-inflammatory properties--properties which should improve airway responsiveness (AR). Conversely, several recent studies have suggested that regular beta 2-agonist treatment may worsen asthma and AR. Furthermore, a short-lived rebound increase in AR has been described following cessation of regular treatment with these agents. We have consequently assessed the effects on AR of regular treatment with either salmeterol or salbutamol at conventional doses over 6 weeks. FEV1 and AR were measured five times in 20 asthmatic subjects randomly allocated to one or other treatment regimen; twice during a 2-week run-in period; and 24 h, 72 h, and 2 weeks after the last dose of the study medication. Peak expiratory flow rate (PEFR) was also recorded throughout the study period. There were no statistically significant changes in FEV1 or AR between the run-in period and any of the post treatment measurements for either of the treatments used. Mean PEFR was significantly higher during the treatment period than the run-in period for the salmeterol group, but not the salbutamol group, confirming that therapeutically adequate doses of salmeterol had been given. We conclude that if the regular use of salmeterol is associated with beneficial or adverse effects on AR, this is not apparent after a treatment period of 6 weeks.

Comparison of the effects of salmeterol and formoterol on airway tone and responsiveness over 24 hours in bronchial asthma

The recent development of new beta 2-adrenoceptor agonists with a duration of action in excess of 12 h may change strategies in the treatment of bronchial asthma. This study aims at the direct comparison of the main representatives of this new class of drugs, formoterol (F) and salmeterol (S), in asthmatic patients over the course of 24 h. Twelve patients with mild bronchial asthma participated in a double-blind, randomized, placebo-controlled clinical trial. In a dose-finding study we determined the protective and bronchodilating effects of 12 and 24 micrograms F aerosol vs 50 and 100 micrograms S 30 min after inhalation. In a 24-h study we investigated the effects of 12 micrograms F and 50 micrograms S on airway tone and responsiveness. Bronchial responsiveness was assessed as the dose of methacholine necessary to decrease FEV1 by 20%. In the dose-finding study, compared with placebo, all doses of F and S equally increased FEV1 (p < 0.003) and protected against inhaled methacholine (p < 0.0001). In the 24-h study 12 micrograms F and 50 micrograms S increased FEV1 and significantly protected against methacholine-induced bronchoconstriction up to 24 h (p < 0.05), compared with placebo. Phase and amplitude of the circadian variation of FEV1 and airway responsiveness were not affected. Clinically recommended doses of aerosolized F (12 micrograms) and S (50 micrograms) have a duration of action up to 24 h and are equally effective at bronchodilation and protection in acute experiments in patients with mild bronchial asthma.

Salmeterol, formoterol, and salbutamol in the isolated guinea pig trachea: differences in maximum relaxant effect and potency but not in functional antagonism

BACKGROUND

Formoterol and salmeterol are new long acting beta 2 adrenoceptor agonists. The maximum relaxant effect, potency and functional antagonism against carbachol induced contraction for salmeterol, formoterol and salbutamol have been compared in the guinea pig isolated trachea. In addition, the possibility of inducing a non-beta adrenoceptor mediated relaxation by salmeterol was studied.

METHODS

Concentration response experiments were conducted with isolated tracheal preparations (n = 4-6 in all experiments), precontracted by carbachol to cause either 40% (60 nmol/l), 80% (0.3 mumol/l) or 100% (3 mumol/l, supramaximal) of the maximum contraction. Each beta agonist was added cumulatively at each level of precontraction. Additional cumulative concentration response experiments were conducted for salmeterol alone at the highest level of precontraction, with and without beta blockade by sotalol (1 mmol/l). With the drug concentrations which produced the maximum response and the highest level of precontraction, the relaxation of formoterol (10 nmol/l) and salmeterol (1 mumol/l) was also compared non-cumulatively. Finally, with the corresponding drug concentrations and precontraction, the relaxant effect was compared for formoterol (10 nmol/l) in salmeterol relaxed airways with that of salmeterol (1 mumol/l) in formoterol relaxed airways.

RESULTS

The increase in carbachol concentration from 60 nmol/l to 3 mumol/l induced a rightward shift in the mean (SE) concentration (log steps) causing 50% maximum relaxation for salmeterol (0.73 (0.17)), formoterol (0.85 (0.18)), and salbutamol (1.13 (0.11)). Significant differences in the maximum relaxant effect were shown at the highest level of precontraction only, with a remaining active tension of percentage precontraction of 27% (4%) for 1 mumol/l salbutamol and 35% (3%) for 10 nmol/l formoterol compared with 50% (2%) for 1 mumol/l salmeterol. The rank order of potency was: formoterol > salbutamol approximately salmeterol at all levels of precontraction (-log EC50: 9.32 (0.05) for formoterol, 7.82 (0.08) for salbutamol, and 7.50 (0.13) for salmeterol at 80% maximum precontraction). Beta blockade by sotalol (1 mmol/l) significantly inhibited the relaxation induced by salmeterol (1 mumol/l) (remaining active tension: 104% (1%) v 71% (11%) of precontraction) but not the relaxation induced by salmeterol (10 mumol/l) (remaining active tension: 75% (5%) v 71% (12%) of precontraction). In the non-cumulative experiments, formoterol displayed more relaxant effect than salmeterol (remaining active tension: 51% (6%) v 65% (6%) of precontraction). Finally, formoterol significantly relaxed salmeterol relaxed airways (relaxant effect: 22% (8%) of precontraction) whereas there was no significant response to salmeterol in formoterol relaxed airways (relaxant effect: 5% (12%) of precontraction).

CONCLUSIONS

In the guinea pig isolated trachea, formoterol and salbutamol produce more relaxant effect than salmeterol, suggesting that salmeterol is a partial beta 2 agonist. Very high concentrations of salmeterol may induce non-beta adrenoceptor mediated relaxation. Formoterol is more potent than both salbutamol and salmeterol. There is no pronounced difference in the magnitude of antagonism against carbachol induced contractions between salmeterol, formoterol, and salbutamol.

Serevent nationwide surveillance study: comparison of salmeterol with salbutamol in asthmatic patients who require regular bronchodilator treatment

OBJECTIVE

To compare safety of salmeterol and salbutamol in treating asthma.

DESIGN

Double blind, randomised clinical trial in parallel groups over 16 weeks.

SETTING

General practices throughout the United Kingdom.

SUBJECTS

25,180 patients with asthma considered to require regular treatment with bronchodilators who were recruited by their general practitioner (n = 3516).

INTERVENTIONS

Salmeterol (Serevent) (50 micrograms twice daily) or salbutamol (200 micrograms four times a day) randomised in the ratio of two patients taking salmeterol to one taking salbutamol. All other drugs including prophylaxis against asthma were continued throughout the study.

MAIN OUTCOME MEASURES

All serious events and reasons for withdrawals (medical and non-medical) whether or not they were considered to be related to the drugs.

RESULTS

Fewer medical withdrawals due to asthma occurred in patients taking salmeterol than in those taking salbutamol (2.91% v 3.79%; chi 2 = 13.6, p = 0.0002). Mortality and admissions to hospital were as expected. There was a small but non-significant excess mortality in the group taking salmeterol and a significant excess of asthma events including deaths in patients with severe asthma on entry. Use of more than two canisters of bronchodilator a month was particularly associated with the occurrence of an adverse asthma event.

CONCLUSIONS

Treatment over 16 weeks with either salmeterol or salbutamol was not associated with an incidence of deaths related to asthma in excess of that predicted. Overall control of asthma was better in patients allocated to salmeterol. Serious adverse events occurred in patients most at risk on entry and were probably due to the disease rather than treatment.

Dose-response study of inhaled salmeterol in asthmatic patients with 24-hour spirometry and Holter monitoring

Salmeterol is a new long-acting beta 2-selective adrenoceptor agonist. In this double-blind, 6-way crossover study, four single doses of salmeterol by metered dose inhaler (12.5, 25, 50, 100 micrograms) were compared with albuterol aerosol 200 micrograms and placebo in 24 patients with moderate asthma with 24-hour pulmonary function testing and Holter monitoring. Salmeterol was an effective bronchodilator at each dose evaluated and demonstrated a greater increase in FEV1 above baseline, a slightly slower onset and a longer duration of bronchodilation than albuterol. Median durations of bronchodilation were 9.0, 15.6, 13.4, and 18.4 hours with increasing doses of salmeterol in comparison to 4.2 hours for albuterol. Holter monitoring showed (1) a mean maximum heart rate 2 to 5 bpm higher after salmeterol 50 and 100 micrograms compared with placebo and (2) supraventricular premature beats (> 30 per hour or > 100 per 24 hours) more often in the salmeterol 100-micrograms group (13% to 17% of patients) than in the placebo (4%), albuterol (4% to 8%), or other salmeterol groups (4% to 9%). These differences were not statistically significant. Tremor and palpitations were the most frequently reported drug-related adverse events and their frequencies increased with increasing doses of salmeterol. This study demonstrated that single doses of salmeterol given by metered dose inhaler over an 8-fold range possess substantial, long-lasting bronchodilator activity.

Determination of salmeterol in rat and dog plasma by high-performance liquid chromatography with fluorescence detection

Salmeterol (as the hydroxynaphthoate) is the first of a new class of long-acting beta-adrenergic receptor agonists with both bronchodilator and anti-inflammatory actions. A sensitive, accurate, and precise high-performance liquid chromatographic method for the determination of salmeterol in rat and dog plasma is described. Samples are prepared by solid-phase extraction and, after chromatography of the extracts on a reversed-phase styrene/divinylbenzene analytical column, salmeterol is detected by fluorescence monitoring (excitation wavelength, 230 nm; emission wavelength, 305 nm). The method is sensitive to 1 ng/mL, at which concentration the coefficient of variation was 16.3% in a single assay run. Repeated analyses of quality control samples, nominally at 2 ng/mL, were carried out over a number of assay runs with a coefficient of variation of 10.4%. The method is specific for salmeterol with respect to endogenous plasma components and identified metabolites. The assay was applied to the analysis of salmeterol in plasma of rats and dogs from pharmacokinetic studies.

Comparative efficacy of salbutamol and salmeterol in exercise-induced asthma

This study compared the protection provided by salbutamol and salmeterol against exercise-induced asthma. Asthmatic patients (n = 12) with exercise-induced asthma were exercised submaximally for 6 min on a treadmill 1, 6 and 12 h after inhalation of 200 micrograms salbutamol or 50 micrograms salmeterol. Each patient also took baseline exercise 1 h after two puffs of placebo. Two days later the drugs were administered in a double-blind trial of crossover design with an interval of 48 h between the two treatments. The main parameters measured were: air flow with a Wright flowmeter and mediator concentrations (histamine, leucotriene and prostaglandin D2 measured by radioimmunoassay) in venous blood, which was withdrawn before and 4 min after each exercise period. The maximum percentage bronchoconstriction recorded following placebo was 29 +/- 4% and following salbutamol inhalation it was 4 +/- 4%, 20 +/- 13%, 27 +/- 10%, respectively, for the exercise periods performed 1, 6 and 12 h after inhalation of the drug. Following salmeterol, the corresponding figures were 3 +/- 4%, 3 +/- 3% and 11 +/- 9%. The concentrations of mediator in plasma were significantly increased after exercise. Salbutamol and salmeterol intake reduced these concentrations both when the patients were at rest and following the exercise period. This effect of both drugs on the mediators corresponded with the protection they provided against exercise-induced asthma and was maintained for 12 h after salmeterol inhalation and for 6 h after salbutamol inhalation.

Interaction and dose equivalence of salbutamol and salmeterol in patients with asthma

OBJECTIVE

To examine the pharmacological interaction of salmeterol and salbutamol and to derive an estimate of dose equivalence of salmeterol for airway and systemic effects in patients with asthma.

DESIGN

Randomised double blind crossover study.

SUBJECTS

12 patients with mild asthma.

INTERVENTION

Placebo or salmeterol 50, 100, 200 micrograms given on separate days followed two hours later by inhaled salbutamol in cumulative doses up to 3600 micrograms.

MAIN OUTCOME MEASURES

Change in forced expiratory volume in one second (FEV1), heart rate, plasma potassium concentration, QTc interval, tremor amplitude, and creatine kinase myocardial isoenzyme concentration.

RESULTS

Compared with placebo, the mean (95% confidence interval) changes in FEV1 and heart rate after salmeterol 200 micrograms were 0.61 (0.32 to 0.90) l and 7.0 (3.8 to 10.2) beats/min. Adding salbutamol caused a large increase in FEV1 after placebo (0.69 l) with progressively smaller changes after increasing doses of salmeterol (0.19 l after salmeterol 200 micrograms). Heart rate and QTc interval increased and plasma potassium concentration decreased roughly in parallel on the four study days with a suggestion of convergence at higher doses of salbutamol. Geometric mean dose equivalences for salmeterol 50 micrograms and 100 micrograms compared with salbutamol were 4.9 and 7.8 (mean 6.4) for FEV1 and ranged from 7.1 (2.9 to 17.0) to 12.6 (4.4 to 36.4) for heart rate, plasma potassium, and tremor (mean 9.5).

CONCLUSIONS

The effect of adding salbutamol to salmeterol is largely additive. Weight for weight salmeterol may be up to 10 times more potent than salbutamol. Considering its longer duration of action salmeterol 50 micrograms twice daily could be equivalent to salbutamol in doses up to 500 micrograms four to six hourly.

Salmeterol is a competitive antagonist at beta-adrenoceptors mediating inhibition of respiratory burst in guinea-pig eosinophils

The ability of the long-acting beta-adrenoceptor agonists eformoterol and salmeterol to inhibit leukotriene (LT) B4 (100 nM; approximately EC70)-induced hydrogen peroxide (H2O2) generation by guinea-pig peritoneal eosinophils was investigated and compared with salbutamol. Eformoterol and salbutamol produced a concentration-dependent inhibition of LTB4-induced H2O2 generation with pIC50 values of 6.22 and > 5.0 respectively. The inhibitory effect eformoterol was mediated through an interaction with beta-adrenoceptors for it was antagonised by propranolol with an affinity (7.21) that was independent of antagonist concentration (100 nM and 1 microM). In contrast, salmeterol (1 nM to 10 microM) failed to inhibit H2O2 generation at any concentration examined irrespective of the pre-incubation time (0, 0.25, 0.5, 1, 2, 15 or 30 min). Salmeterol did, however, competitively antagonise (slope of Schild plot = 0.91) the inhibition of H2O2 generation induced by eformoterol with a pA2 of 5.9. Possible explanations for the lack of inhibitory effect of salmeterol on LTB4-induced respiratory burst are advanced and critically discussed.

The effects of salmeterol and salbutamol on ciliary beat frequency of cultured human bronchial epithelial cells, in vitro

Studies investigating mechanisms of mucociliary clearance have suggested that beta 2-adrenergic agents may significantly influence ciliary activity of epithelial cells and therefore play a vital role in the maintenance of functional integrity of the airways. We have cultured human bronchial epithelial cells, from surgical explants and investigated the effects of salbutamol and salmeterol, in a time- and dose-dependent manner, on the ciliary beat frequency (CBF) of these cells. Prior to and at several times after exposure to either salbutamol (10(-8) to 10(-3) M) or salmeterol (10(-8) to 10(-4) M), the epithelial cells were monitored for CBF and on the basis of data obtained from these studies, the effect of 10(-6) M propranolol was investigated in the presence of optimal concentrations of salbutamol and salmeterol. Salbutamol was optimally active at a concentration of 10(-4) M and caused a transient but significant increase in the CBF from baseline level of 8.6 +/- 0.4 to 9.6 +/- 0.5 Hz (P < 0.05), after 2 h incubation. In contrast, salmeterol was maximally active at a concentration of 10(-6) M and caused a significantly rapid and prolonged increase in CBF from a baseline value of 9.2 +/- 0.4 to 10.9 +/- 0.6 Hz (P < 0.02) and 10.6 +/- 0.8 Hz (P < 0.05) after 15 min and 24 h incubation, respectively. Propranolol (10(-6) M) abrogated the salbutamol- but not the salmeterol-induced increases in CBF.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigations into factors determining the duration of action of the beta 2-adrenoceptor agonist, salmeterol

1. This study has explored the mechanism underlying the long duration of action of the beta 2-adrenoceptor agonist, salmeterol. 2. Salmeterol, salbutamol and isoprenaline caused a concentration-related inhibition of electrically-induced contractile responses of the guinea-pig superfused trachea preparation. The effects of both isoprenaline and salbutamol were rapid in onset and rapidly reversed upon removal of the agonist. In contrast, the effects of salmeterol were slower in onset and could not be reversed by superfusion of the tissue with agonist-free Krebs solution even for periods of up to 10 h. 3. The effects of salmeterol were, however, readily reversed by a number of beta-adrenoceptor blocking drugs, as was the effect of a continuous infusion of isoprenaline. Upon removal of the antagonist, however, the effects of salmeterol and of the isoprenaline infusion were reasserted at a rate which was inversely related to the lipophilicity of a beta-adrenoceptor blocking drugs. 4. Salmeterol inhibited the binding of [125I]-(-)-iodopindolol (100 pM) to rat lung membranes (pIC50 7.1), with isoprenaline (pIC50 6.2) and salbutamol (pIC50 5.1) having lower potencies. The inhibition of binding by salmeterol was apparently non-competitive, whereas that produced by salbutamol and isoprenaline was competitive in nature. 5. Isoprenaline and salbutamol rapidly dissociated from their binding sites, whereas in marked contrast, the binding of salmeterol showed no dissociation for periods of up to 1 h. 6. These data are consistent with the mechanism in which salmeterol binds adjacent to the active site of the beta 2-adrenoceptor, such that the drug cannot be washed out of the tissue, yet can interact with and activate the receptor. This latter property is susceptible to antagonism by beta-adrenoceptor blocking drugs but is reassured when the antagonists are removed.

Twelve month comparison of salmeterol and salbutamol as dry powder formulations in asthmatic patients. European Study Group

BACKGROUND

Salmeterol is a potent selective beta 2 agonist that has been shown to have a duration of action in excess of 12 hours. In this study salmeterol and salbutamol were compared over a three month period with a further extension of nine months.

METHODS

Three hundred and eighty eight patients with mild to moderate reversible airways obstruction (forced expiratory volume in one second (FEV1) > 50% predicted) were randomised to receive salmeterol (50 micrograms) twice daily or salbutamol (400 micrograms) four times daily, both by dry powder, in a double blind parallel group study. During the first three months detailed assessment of efficacy was made with recording of morning and evening peak expiratory flow rates (PEF), asthma symptoms, and bronchodilator use when necessary for the relief of symptoms. Patients continued in the study for a further nine months with the salbutamol dose reduced to 400 micrograms twice daily. Lung function was measured at the clinic and safety data were collected during this period.

RESULTS

Salmeterol produced a significantly higher mean morning PEF (mean difference compared with salbutamol 21 (95% CI 12-31) l/min), and a significant reduction in mean diurnal variation in PEF (from 30 l/min at baseline to 11 34 l/min at baseline to 32 l/min during salbutamol treatment). Salmeterol also reduced day and night symptoms and use of rescue bronchodilator. FEV1 increased with both salmeterol and salbutamol treatment over the 12 month treatment period. For both treatments the number of patients reporting exacerbations of asthma and the frequency of these exacerbations remained constant during the study. Thirty six patients in the salmeterol and 49 in the salbutamol group withdrew during the 12 months of the study.

CONCLUSIONS

In this study salmeterol (50 micrograms twice daily) was more effective than salbutamol (400 micrograms four times daily) in the control of asthma over three months, and more effective than salbutamol (400 micrograms twice daily) over a further nine months. Neither salmeterol nor salbutamol was associated with any worsening of control of asthma.

Failure of salmeterol to inhibit circulating white cell responses and bronchoconstriction induced by platelet activating factor

BACKGROUND

Platelet activating factor (PAF) is a potent mediator of inflammation. Inhalation of PAF causes acute bronchoconstriction and a transient fall in white blood cell count in humans. Salmeterol inhibits pulmonary inflammation induced by PAF in guinea pigs.

METHODS

The effect of salmeterol on effects induced by PAF was investigated in eight normal subjects who inhaled salmeterol (50 micrograms) twice daily or a matched placebo for one week before challenge with PAF. Blood samples were taken from a forearm catheter for total white cell and neutrophil counts before and for 30 minutes after administration of PAF (48 micrograms) through a Mefar dosimeter. Blood films were stained for unsegmented neutrophils before and after treatment with PAF on a placebo day.

RESULTS

Mean baseline total white cell counts and neutrophil counts did not differ on the two days. Mean baseline sGaw was significantly higher after inhaled salmeterol (1.84 (95% C1 1.45-2.23) s-1kPa-1) than after placebo (1.53 (1.24-1.82)). After placebo mean total white cell counts, neutrophil counts, and sGaw were reduced to 60 (43-78)%, 39 (14-64)%, and 82 (71-93)% of baseline respectively five minutes after inhaled PAF. After salmeterol treatment mean reductions five minutes after inhaled PAF were 59 (45-73)%, 40 (19-61)%, and 82 (71-93)% of baseline respectively. At 30 minutes after treatment with PAF the neutrophil count rebounded to 143 (82-204)% of baseline after placebo and to 127 (93-161)% after inhaled salmeterol. There was no significant difference in the percentage of immature neutrophils before and after treatment with PAF (2.0 (0.5-2.6)% compared with 3.9 (2.2-5.6)%.

CONCLUSIONS

Treatment with salmeterol did not inhibit reduction in total white cell count or neutrophil count, rebound neutrophilia, acute bronchoconstriction, or transient flushing after inhalation of PAF. These results conflict with the inhibitory effect of salmeterol on lung inflammation in guinea pigs but are consistent with the lack of effect of salbutamol in humans. Salmeterol does not have an anti-PAF effect in vivo in humans.

Inhaled salmeterol in the treatment of patients with moderate to severe reversible obstructive airways disease--a 3-month comparison of the efficacy and safety of twice-daily salmeterol (100 micrograms) with salmeterol (50 micrograms)

Three-hundred and fifty patients with moderate to severe reversible obstructive airways disease (forced expiratory volume in 1 s or peak expiratory flow rate < or = 50% predicted, a 15% reversibility to inhaled salbutamol and symptomatic) were recruited into a multi-centre, multinational, double-blind, parallel-group randomized study. Two-hundred and eighty-three patients were randomized to receive 50 micrograms salmeterol twice daily or 100 micrograms salmeterol twice daily administered from a metered-dose inhaler for 3 months. Salbutamol (100 micrograms per metered actuation) was provided for symptomatic relief. Morning and evening peak expiratory flow rate (PEFR), day-time and night-time asthma symptoms and additional bronchodilator usage were recorded by the patient on a daily basis. Lung function and patient/physician assessment of treatment efficacy were recorded at scheduled clinic visits. Safety was determined by monitoring adverse events and standard biochemical, haematological and cardiovascular parameters. Salmeterol 100 micrograms twice daily was consistently superior to salmeterol 50 micrograms twice daily in morning and evening PEFR measurements (mean differences between the treatments: 10-14 l min-1 for morning, 95% CI-0, 22 l min-1, P = 0.047; and 10-15 l min-1 for evening, 95% CI 2, 22 l min-1, P = 0.023). The improvement in PEFR was independent of concurrent steroid usage, with the most marked improvement being seen in the more severe asthmatics requiring concurrent oral corticosteroids (mean differences between the treatments: 27-31 l min-1, 95% CI: 3,55 l m-1, P = 0.027).(ABSTRACT TRUNCATED AT 250 WORDS)

Long acting inhaled beta-adrenoceptor agonists the comparative pharmacology of formoterol and salmeterol

Formoterol and salmeterol are chemically distinct, highly selective beta-2-adrenoceptor agonists developed to provide sustained (12h+) relief of airway obstruction in diseases such as asthma. Despite their similar long duration of action, these drugs differ. Formoterol has a faster onset of action in both experimental and clinical tests than that of salmeterol. Salmeterol, but not formoterol, behaves as a beta-adrenoceptor antagonist in some experimental models due to its considerably weaker efficacy at the beta 2-adrenoceptor in vitro although their are no established clinical consequences of this antagonism. Both formoterol and salmeterol display a peculiar "reassertion" behaviour in isolated airway smooth muscle subjected to beta-adrenoceptor antagonism and then washed with antagonist-free buffer. Both formoterol and salmeterol are highly efficient inhibitors of a number of indices of acute inflammatory processes in cells and tissues of human or animal origin. However, neither of these drugs has a proven clinical anti-inflammatory effect in chronic asthma in humans. Surprisingly, recent biophysical studies of formoterol and salmeterol have provided strong evidence that their individual patterns of onset speed, duration of action and "reassertion" are due to a common drug-lipid membrane interaction rather than drug-adrenoceptor interactions. A membrane-drug diffusion microkinetic model is presented to describe these phenomena.

Clinical pharmacology of long-acting beta-receptor agonists

The longer-acting beta-receptor agonists salmeterol and formoterol are effective bronchodilators for at least 12 hours and this should be clinically useful, particularly for nocturnal asthma. Formoterol has a more rapid onset than salmeterol. There are limited dose response data on the two drugs in man but the evidence so far suggests that both drugs have roughly similar beta 2-selectivity to salbutamol and that both are about ten times as potent as salbutamol. Salmeterol may therefore have been marketed at a relatively high dose compared to salbutamol. There is no good clinical evidence to suggest that the drugs have effects other than would be expected from a beta 2-agonist with a prolonged duration of action. Medium-term studies have shown that benefit was maintained in comparison to salbutamol and, in one instance, with salmeterol when compared to placebo. Studies to date have not found any reduction in the bronchodilator response to salbutamol following regular treatment with salmeterol or formoterol, though one study has found reduced protection by salmeterol against methacholine challenge after one and two months' treatment. Longer-term safety has not been assessed.

Effect of a single dose of inhaled salmeterol on baseline airway caliber and methacholine-induced airway obstruction in asthmatic children

BACKGROUND

Salmeterol is a new inhaled selective beta 2-adrenergic receptor agonist with a long duration of action. We studied the duration of the bronchodilation and the protective effect against methacholine-induced airway obstruction of a single dose of salmeterol in a double-blind, randomized, placebo-controlled, crossover design.

METHODS

Seventeen boys and three girls with mild-to-moderate asthma participated in the study. On two separate days either 50 micrograms salmeterol or placebo was inhaled. FEV1 and PD20 methacholine were determined before and 1, 4, 8, 12, and 24 hours after inhalation.

RESULTS

Salmeterol resulted in a significant bronchodilation compared with placebo, up to 12 hours (p = 0.0001). At 24 hours there was a residual effect that approached significance; mean FEV1 being 8.3% +/- 2.4% above baseline (p = 0.06). Significant protection against airway sensitivity to methacholine after salmeterol inhalation was found at all time points (p < 0.005). Twenty-four hours after administration mean PD20 was still 1.22 +/- 0.29 doubling dose above baseline. No important adverse effects were noted.

CONCLUSION

We conclude that a single dose of 50 micrograms salmeterol in children with asthma gives a long-lasting bronchodilation, exceeding 12 hours, which is comparable to the results in adult studies. The duration of the protection against airway sensitivity to methacholine exceeds 24 hours.