Bambuterol: effective in nocturnal asthma

Asthma and COPD: A Focus on β-Agonists - Past, Present and Future

Asthma has been recognised as a respiratory disorder for millennia and the focus of targeted drug development for the last 120 years. Asthma is one of the most common chronic non-communicable diseases worldwide. Chronic obstructive pulmonary disease (COPD), a leading cause of morbidity and mortality worldwide, is caused by exposure to tobacco smoke and other noxious particles and exerts a substantial economic and social burden. This chapter reviews the development of the treatments of asthma and COPD particularly focussing on the β-agonists, from the isolation of adrenaline, through the development of generations of short- and long-acting β-agonists. It reviews asthma death epidemics, considers the intrinsic efficacy of clinical compounds, and charts the improvement in selectivity and duration of action that has led to our current medications. Important β2-agonist compounds no longer used are considered, including some with additional properties, and how the different pharmacological properties of current β2-agonists underpin their different places in treatment guidelines. Finally, it concludes with a look forward to future developments that could improve the β-agonists still further, including extending their availability to areas of the world with less readily accessible healthcare.

A genome-wide association study of bronchodilator response in asthmatics

Reversibility of airway obstruction in response to β2-agonists is highly variable among asthmatics, which is partially attributed to genetic factors. In a genome-wide association study of acute bronchodilator response (BDR) to inhaled albuterol, 534 290 single-nucleotide polymorphisms (SNPs) were tested in 403 white trios from the Childhood Asthma Management Program using five statistical models to determine the most robust genetic associations. The primary replication phase included 1397 polymorphisms in three asthma trials (pooled n=764). The second replication phase tested 13 SNPs in three additional asthma populations (n=241, n=215 and n=592). An intergenic SNP on chromosome 10, rs11252394, proximal to several excellent biological candidates, significantly replicated (P=1.98 × 10(-7)) in the primary replication trials. An intronic SNP (rs6988229) in the collagen (COL22A1) locus also provided strong replication signals (P=8.51 × 10(-6)). This study applied a robust approach for testing the genetic basis of BDR and identified novel loci associated with this drug response in asthmatics.

Long-acting beta-agonist treatment in patients with persistent asthma already receiving inhaled corticosteroids

International guidelines recommend that long-acting beta-agonists should be considered in patients who are symptomatic despite moderate doses of inhaled corticosteroids. When combined with inhaled corticosteroids they improve asthma symptoms and lung function and reduce exacerbations. The evidence suggests that they are well tolerated. However, they are less effective than inhaled corticosteroids as monotherapy and should not be used alone, although the addition of a long-acting beta-agonist may permit a small reduction in the corticosteroid dose. Both salmeterol and formoterol appear equally effective in improving asthma control. Formoterol, however, has a rapid onset of action and is now being promoted for the relief of acute asthma symptoms. Both drugs provide prolonged protection against exercise-induced bronchospasm. However, this effect rapidly diminishes with continuous therapy and if this is the main aim of treatment, intermittent use may be preferable. When compared with alternative treatments, inhaled long-acting beta-agonists are more effective in controlling asthma symptoms than either theophylline or antileukotriene agents. Bambuterol, an oral prodrug of terbutaline, appears to be as effective as the inhaled long-acting beta-agonists and has the advantage of once daily oral administration. However, the inhaled long-acting beta-agonists are less likely to have systemic adverse effects. There are theoretical concerns that regular beta-agonist treatment may lead to tolerance and a failure to respond to emergency asthma treatment. While there is no doubt that tolerance occurs, there is currently little evidence that this is a clinical problem. Insights into pharmacological as well as therapeutic interactions between inhaled corticosteroids and beta-agonists are providing justification for their use in combination. Guidelines for the management of patients with chronic persistent asthma are likely to require modification to reflect these developments.

Nocturnal asthma uncontrolled by inhaled corticosteroids: theophylline or long-acting beta2 agonists?

Asthma is an inflammatory disease of the airways that is frequently characterised by marked circadian rhythm. Nocturnal and early morning symptoms are quite common among patients with asthma. Increased mortality and decreased quality of life are associated with nocturnal asthma. Although numerous mechanisms contribute to the pathophysiology of nocturnal asthma, increasing evidence suggests the most important mechanisms relate to airway inflammation. According to international guidelines, patients with persistent asthma should receive long term daily anti-inflammatory therapy. A therapeutic trial with anti-inflammatory therapy alone (without a long-acting bronchodilator) should be assessed to determine if this therapy will eliminate nocturnal and early morning symptoms. If environmental control and low to moderate doses of inhaled corticosteroids do not eliminate nocturnal symptoms, the addition of a long-acting bronchodilator is warranted. Long-acting inhaled beta2 agonists (e.g. salmeterol, formoterol) are effective in managing nocturnal asthma that is inadequately controlled by anti-inflammatory agents. In addition, sustained release theophylline and controlled release oral beta2 agonists are effective. In patients with nocturnal symptoms despite low to high doses of inhaled corticosteroids, the addition of salmeterol has been demonstrated to be superior to doubling the inhaled corticosteroid dose. In trials comparing salmeterol with theophylline, 3 studies revealed salmeterol was superior to theophylline (as measured by e.g. morning peak expiratory flow, percent decrease in awakenings, and need for rescue salbutamol), whereas 2 studies found the therapies of equal efficacy. Studies comparing salmeterol to oral long-acting beta2 agonists reveal salmeterol to be superior to terbutaline and equivalent in efficacy to other oral agents. Microarousals unrelated to asthma are consistently increased when theophylline is compared to salmeterol in laboratory sleep studies. In addition to efficacy data, clinicians must weigh benefits and risks in choosing therapy for nocturnal asthma. Long-acting inhaled beta2 agonists are generally well tolerated. If theophylline therapy is to be used safely, clinicians must be quite familiar with numerous factors that alter clearance of this drug, and they must be prepared to use appropriate doses and monitor serum concentrations. Comparative studies using validated, disease specific quality of life instruments (e.g. Asthma Quality of Life Questionnaire) have shown long-acting inhaled beta2 agonists are preferred to other long-acting bronchodilators. Examination of costs for these therapeutic options reveals that evening only doses of long-acting oral bronchodilators are less expensive than multiple inhaled doses. However, costs of monitoring serum concentrations, risks, quality of life and otheroutcome measures must also be considered. Long-acting inhaled beta2 agonists are the agents of choice for managing nocturnal asthma in patients who are symptomatic despite anti-inflammatory agents and other standard management (e.g. environmental control). These agents offer a high degree of efficacy along with a good margin of safety and improved quality of life.

Comparative study using oral solutions of bambuterol once daily or terbutaline three times daily in 2-5-year-old children with asthma. Bambuterol Multicentre Study Group

The aim of this study was to compare safety and efficacy of bambuterol hydrochloride (10 mg) oral solution administered once daily in the evening with terbutaline sulphate (0.075 mg/kg body weight) oral solution administered three times daily in 2-5-year-old children with asthma. There were two treatment groups: (2/3) of the patients received bambuterol and (1/3) received terbutaline. The study was double-blind, randomized, and of a parallel group design, and it lasted for 3 months after a 2-week run-in period. The primary objective was to evaluate safety (adverse events, and changes in blood pressure, pulse rate, hematology, and clinical chemistry parameters). Plasma concentrations of terbutaline and/or bambuterol were also measured. Evaluation of efficacy (diary card data) was a secondary objective. A total of 155 patients (range, 2-6 years; 3 patients were 6 years old at randomization) were treated with the study drugs; 104 patients received bambuterol and 51 patients received terbutaline. Both treatments showed a good safety profile with respect to clinical and laboratory tests, and they were generally well tolerated. Reported adverse events were mild to moderate. There were no statistically significant differences between treatment groups in any of the efficacy variables (diary variables: peak expiratory flow (PEF), asthma symptoms, restlessness, other reported symptoms, use of inhaled bronchodilators, and nighttime awakenings). For morning PEF, the mean increase from run-in to treatment was 16.9 L/min in the terbutaline group and 23.3 L/min in the bambuterol group. For evening PEF, the mean increase was 20.2 L/min in the terbutaline group and 20.6 L/min in the bambuterol group. In conclusion, once-daily bambuterol is as safe and effective as terbutaline given three times daily. The study also confirmed that bambuterol has a 24-hr duration of action, and therefore its once daily administration, makes it a preferred bronchodilator agent. Pediatr Pulmonol. 2000:29:194-201.

Circadian rhythms in the pharmacokinetics and clinical effects of beta-agonist, theophylline, and anticholinergic medications in the treatment of nocturnal asthma

Published asthma consensus reports now acknowledge that asthma is a nocturnal disease in as many as 75% of those afflicted by this medical condition. Nonetheless, the treatment of this chronic obstructive pulmonary disease in the clinic continues to be based primarily on homeostatic considerations in that it relies on long-acting bronchodilator and other therapies formulated and scheduled to ensure constant or near-constant levels of medication during the 24h. The need of asthma patients prone to nighttime attacks is not the same during the day and night; the therapeutic requirements of patients who experience nocturnal asthma, especially ones with the more severe forms of the disease, are often not satisfied by conventional medications. The therapeutic response and patient tolerance to bronchodilator medications can be improved markedly when the medications are proportioned during the 24h as a chronotherapy, that is, when more medication is delivered during nighttime sleep than daytime activity, as verified by numerous studies. This article reviews how the body's circadian rhythms influence the pharmacokinetics and effects of commonly prescribed asthma therapies and addresses why and how they must be taken into consideration to increase the effectiveness of asthma treatment.

Pharmacokinetics of bambuterol during oral administration to asthmatic children

AIMS

To investigate dose proportionality, dosing frequency, and ethnic aspects of the pharmacokinetics of bambuterol in asthmatic children, and to discuss the relationship with previous observations in adults.

METHODS

Forty-eight children in four different studies completed two double-blind bambuterol treatments each (daily doses of bambuterol hydrochloride): 12 preschool (5 mg x 2 vs 10 mg) and 12 school (10 mg vs 20 mg) Caucasians, 12 preschool (2.5 mg vs 5 mg), and 12 school (10 mg vs 20 mg) Orientals. Peak plasma concentrations and dosing interval area under curve (AUC) of bambuterol and the active metabolite terbutaline were assessed at steady state. Treatment differences were analysed statistically within each study. Differences between the studies and the relation to steady-state AUC in adults were described.

RESULTS

Dose proportionality was seen for terbutaline but not for bambuterol. Twice-daily dosing (2 x AUC(0,12 h)) could not be shown to differ from once-daily dosing (AUC(0,24 h)) in the preschool Caucasians. Mean AUC of terbutaline was 128 and 242 nmol l-1 h in the preschool Caucasians (5 mg/12 h; 10 mg/24 h), 213 and 406 nmol l-1 h in the Caucasian school children (10 mg; 20 mg), 87.4 and 202 nmol l-1 h in the Oriental preschool children (2.5 mg; 5 mg), and 356 and 640 nmol l-1 h in the Oriental school children (10 mg; 20 mg). Oriental school children had higher plasma concentrations of bambuterol and terbutaline than Caucasian school children. The strict ethnic implication of the difference could not be elucidated, because demographic data were not perfectly matched. Terbutaline AUC was only moderately increased in the Caucasian school children compared with Caucasian adults. The increase was more pronounced in Oriental children and in some preschool Caucasians. The highest concentration of terbutaline, 58 nmol l-1, was seen in an Oriental school child after a 20 mg dose.

CONCLUSIONS

Caucasian school children can be given bambuterol hydrochloride very much as Caucasian adults, 10 or 20 mg once daily, but Oriental preschool and school children plus preschool Caucasians should be given lower doses.

Comparison of oral bambuterol and inhaled salmeterol in patients with symptomatic asthma and using inhaled corticosteroids

Salmeterol inhaled twice-daily is now being used more frequently as additional treatment in asthma insufficiently controlled by inhaled corticosteroids. We compared oral bambuterol in a dose of 20 mg taken once daily in the evening with inhaled salmeterol at 50 microgram taken twice daily in 126 asthmatic patients (60 bambuterol, 66 salmeterol) aged 18 to 74 yr who were treated for at least 4 wk with inhaled corticosteroids at a constant dose of 400 to 2,000 microgram/d or with oral corticosteroids at </= 20 mg/d. The patients were able to use a pressurized metered dose inhaler (pMDI) efficiently, and had an FEV1 of 40 to 85% of the predicted normal value. During a run-in period, patients had to show at least one nocturnal or early awakening caused by asthma symptoms that required rescue medication, and a >/= 15% overnight decrease in peak expiratory flow (PEF) on 3 of the preceding 7 d, in order to be randomized into this double-blind, double dummy, multicenter parallel group study (2-wk run-in period and 6 wk of treatment). There was no significant difference between bambuterol and salmeterol in morning change from baseline in PEF (p = 0.53). The median increases in morning PEF were 50 L/min for bambuterol and 55 L/min for salmeterol. Other variables (evening PEF, percent of overnight decrease in PEF, number of awakenings, percent of nights with an awakening, number of puffs of rescue medication, asthma symptoms during the day and night, and mean tremor score) also showed no significant difference between bambuterol and salmeterol. Both treatments, at the doses given, were well tolerated. Once-daily oral bambuterol is a convenient, effective, and less expensive alternative to twice-daily inhaled salmeterol for treating nocturnal asthma.

A comparison of two long-acting beta-agonists, oral bambuterol and inhaled salmeterol, in the treatment of moderate to severe asthmatic patients with nocturnal symptoms. The French Bambuterol Study Group

This multicentre study was set up to compare the efficacies of two long-acting beta 2-agonists, oral bambuterol (20 mg nocte) and inhaled salmeterol (50 micrograms b.i.d.), for the treatment of moderate to severe asthmatics who were considered to be on optimal steroid/bronchodilator therapy, but continued to have troublesome nocturnal symptoms. The study was of double-blind, parallel-group design and comprised a 2-week run-in on previous maintenance therapy followed by a 6-week study treatment period. There were 117 randomized asthmatic patients aged 20-70 years (65 women and 52 men with a mean age of 45 and predicted FEV1 of 64%), who had been taking 800-2000 micrograms inhaled steroid and/or up to 20 mg oral steroid per day for at least 4 weeks. They were asked to complete daily diary cards, recording morning and evening PEF, daily symptoms, nocturnal awakenings, rescue medication and subjective tremor. There was a significant increase in both morning and evening PEF respectively, on bambuterol (28 l min-1, 20 l min-1, P < 0.05) and salmeterol (29 l min-1, P < 0.001; 23 l min-1, P < 0.01) when compared with run-in. The mean percentage fall in overnight PEF was reduced by 8.3% (P < 0.001) on bambuterol and by 6.8% (P < 0.001) on salmeterol. Nocturnal awakenings and daytime symptoms due to asthma were significantly lowered by both treatments, as was the consumption of rescue bronchodilator. Tremor scores were very low during both run-in and study treatments. No significant treatment difference between bambuterol and salmeterol was detected for any of the above variables. Once-daily oral bambuterol provides a highly effective alternative to twice-daily inhaled salmeterol for relief of nocturnal symptoms in patients with moderate to severe asthma.

Pharmacokinetics of bambuterol in healthy subjects

AIMS

To study the pharmacokinetics and bioavailability of the prodrug bambuterol and its bronchodilator moiety terbutaline in healthy subjects.

METHODS

Eight healthy subjects (four women) received intravenous doses of bambuterol and terbutaline. On a third occasion, they, plus another four subjects, ingested oral bambuterol as a single dose followed by repeated doses once daily for 7 days. Plasma concentrations and urinary excretion of bambuterol and terbutaline were measured.

RESULTS

After intravenous administration, renal clearances of bambuterol and terbutaline were similar (about 140 ml min(-1)), but there was a five-fold difference in total clearance (bambuterol 1.25 l min(-1), terbutaline 0.23 l min(-1)). Volume of distribution (Vss) was 1.6 l kg(-1) b.w. for both substances. A similar renal clearance of bambuterol was found during oral administration but that of terbutaline decreased (to about 120 ml min(-1)). Mean terminal half-life of bambuterol was 2.6 h after intravenous and 12 h after oral administration, implying that uptake was rate-limiting. Mean residence time of terbutaline generated from oral bambuterol was 34 h compared with 8.0 h when terbutaline as such was infused. Generated terbutaline had a bioavailability of 36% (28-46) after intravenous and 10.2% (6.1-13.2) after oral administration of the prodrug. Bambuterol was well tolerated. The mean activity of plasma cholinesterase, an enzyme catalyzing bambuterol metabolism, was inhibited between 30-60% during repeated oral dosing. It virtually regained original activity within 48 h after the last dose.

CONCLUSIONS

The plasma concentration ofterbutaline fluctuated little during repeated oral administration (mean peak: trough ratio 1.9), as a result of prolonged absorption of bambuterol and slow formation of terbutaline. Thus, the pharmacokinetic properties of bambuterol make it suitable for oral once-daily dosage.

Clinical pharmacokinetics of bambuterol

Bambuterol, a biscarbamate ester prodrug of the beta 2 adrenergic agonist terbutaline, has been approved for the treatment of asthma in 28 countries. It is available in 10 and 20mg (25 and 50 mumol) tablets as the hydrochloride salt. Bambuterol is stable to presystemic elimination and is concentrated by lung tissue after absorption from the gastrointestinal tract. The prodrug is hydrolysed to terbutaline primarily by butyrylcholinesterase, and lung tissue is capable of this metabolic pathway. It is also oxidatively metabolised to products which can be hydrolysed to terbutaline. Peak terbutaline plasma concentrations occur 3.9 to 6.8 hours after bambuterol ingestion, and the peak: trough terbutaline concentration ratio is lower than that after ingestion of terbutaline. Older patients have a greater area under the plasma concentration-time curve for terbutaline over a dose interval at steady-state. Whether genetic variations in the expression of butyrylcholinesterase alter therapeutic response remains to be determined. The efficacy of bambuterol has been demonstrated to last for 24 hours after ingestion; once-daily administration in the evening is recommended. Maximum therapeutic benefit requires more than 1 week of treatment. Except for the suppression of plasma butyrylcholinesterase, the adverse effect profile of bambuterol is essentially that of a beta 2 agonist and is best correlated with circulating terbutaline concentration in plasma. Plasma butyrylcholinesterase activity returns to control values approximately 2 weeks after discontinuation of treatment with bambuterol. This new drug provides oral beta 2 agonist therapy in a more convenient form than was available previously, and may have a better therapeutic: toxic ratio than terbutaline.

Comparison of the efficacy, tolerability and patient acceptability of once-daily bambuterol tablets against twice-daily controlled release salbutamol in nocturnal asthma. ACROBATICS Research Group

The aim of the study was to compare the efficacy, tolerability and patient acceptability of bambuterol (Bambec) against controlled release (CR) salbutamol (Volmax) in the treatment of nocturnal asthma. One hundred and fifty two asthmatic patients aged 17-78 years, using > or = 800 micrograms/day of an inhaled steroid, with nocturnal asthma symptoms, openly received three weeks of bambuterol 20 mg nocte and three weeks of salbutamol CR 8 mg b.i.d. in a randomised, cross over sequence. Both bambuterol and salbutamol CR treatment produced a significant 63% decrease in the severity of baseline nocturnal asthma symptoms. This improved control of nocturnal asthma was reflected by significant improvements in baseline lung function. Both the severity and number of days of tremor during the first week of treatment was significantly lower with bambuterol than with salbutamol CR. Patients considered bambuterol to cause less shakiness and treatment preference was bambuterol 49%, salbutamol CR 36%, no preference 15%. The predominant reason for patient treatment preference was control of asthma symptoms, however a significant sub-group of patients (27%) chose bambuterol because of fewer adverse effects compared to 11% choosing salbutamol CR. Fifty six percent of patients preferred taking their medication once-daily and 7% preferred twice-daily. This study shows that both bambuterol and salbutamol CR are equally effective treatments for nocturnal asthma in patients already receiving inhaled steroid. The most important factor in terms of patient treatment acceptability appears to be control of symptoms. Sub-groups of patients may chose bambuterol due to its better adverse effect profile and once-daily regimen.