Prolonged bronchoprotection against inhaled methacholine by inhaled BI 1744, a long-acting β₂-agonist, in patients with mild asthma

Article Outline

• Abstract
• Methods
  • Subjects
  • Design
  • Laboratory procedures
    • Study medication
    • Lung function measurements
    • Methacholine inhalation challenge
  • Statistical analysis
• Results
• Discussion
• Acknowledgment
• References
• Copyright

Background

Long-acting ß₂-agonists are an established controller medication in asthma. BI 1744 is a novel L\long-acting ß₂-agonist with a preclinical profile that suggests 24-hour bronchodilation and bronchoprotection may be achieved.

Objective

To examine the bronchoprotective effects of single doses of BI 1744 against methacholine provocation in subjects with mild asthma.

Methods

Thirty-one subjects with mild asthma were randomized to receive single doses of BI 1744 (2, 5, 10, 20 μg) or placebo on separate days according to a double-blind, 5-way crossover design. Methacholine challenges were performed at 30 minutes and at 4, 8, 24, and 32 hours after each single dose of medication, and the results were expressed as PC₂₀ FEV₁.

Results

All doses of BI 1744 produced statistically significant increases in the methacholine PC₂₀ compared with placebo as long as 32 hours. The mean (geometric SEM) methacholine PC₂₀ 24 hours after dosing with placebo was 1.73 (1.13) mg/mL, which increased after 2 μg to 3.86 (1.14) mg/mL, after 5 μg to 5.67 (1.14) mg/mL, after 10 μg to 9.42 (1.13) mg/mL, and after 20 μg to 13.71 (1.14) mg/mL (all P < .0001). After 32 hours, the methacholine PC₂₀ value remained significantly increased for all doses. No safety or tolerability concerns were identified.

Conclusion

BI 1744 provides significant bronchoprotection against inhaled methacholine for up to 32 hours after single-dose administration.

Key words: Asthma, long-acting inhaled β₂-agonists, methacholine, functional antagonists, bronchodilators

Abbreviations used: AE, Adverse event, LABA, Long-acting ß₂-agonist

β₂-Adrenoceptors agonists are potent bronchodilators and are a mainstay of asthma treatment. Rapid-onset β₂-agonists are recommended by asthma treatment guidelines as relief medication¹ but are also effective functional antagonists by partially protecting against bronchoconstrictor stimuli such as exercise² or cold air.³ Over the past 10 years, there has been an increasing awareness that long-acting inhaled β₂-agonists (LABAs) are also controller medications when combined with inhaled corticosteroids, because this combination reduces the risks of severe asthma exacerbations⁴, ⁵ and improved asthma control⁶ compared with similar doses of inhaled corticosteroid alone. Two LABAs have been available for asthma treatment, formoterol⁷ and salmeterol,⁸ both of which have a duration of action as a bronchodilator or functional antagonist of about 12 hours⁷, ⁸ and therefore must be administered twice daily.

The proven value of LABAs as controller medications for asthma, as well as their efficacy in chronic obstructive pulmonary disease,⁹ has resulted in the development of LABAs with pharmacologic properties of prolonged duration of action, which would potentially make them once-a-day medications. BI 1744 is a LABA with topical lung selectivity, is almost a full agonist at β₂-adreneceptors and highly β₂-selective, and has a preclinical profile consistent with once-daily administration.

Evaluating the duration of efficacy of a LABA should include the potential of both prolonged bronchodilation and bronchoprotection. Patients with mild asthma should have close to normal lung function and therefore are not an ideal population for evaluating the duration of bronchodilation. By contrast, patients with mild asthma will have methacholine airway hyperresponsiveness¹⁰ of a degree that a shift in the dose-response to inhaled methacholine can be demonstrated with inhaled β₂-agonists (functional antagonism), and the duration of this effect can be quantified.¹¹ Thus, the purpose of this study was to examine the magnitude and duration of functional antagonism provided by BI 1744 as measured by its ability to protect against bronchoconstriction induced by inhaled methacholine in subjects with mild, stable asthma over a period of 32 hours after administration of a range of single doses (2 μg, 5 μg, 10 μg, and 20 μg).

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Methods 

Subjects 

Thirty-one subjects with mild, stable asthma were randomized to treatment (Table I). All subjects had a diagnosis of intermittent asthma according to the Global Initiative for Asthma.¹ No subject was using maintenance treatment for asthma, and all were using intermittent (less than daily) inhaled β₂-agonist use for rescue. All had a prebronchodilator FEV₁ of ≥80% predicted normal¹² and methacholine airway hyperresponsiveness with PC₂₀ FEV₁ ≤ 8 mg/mL (Table I). All subjects were either nonsmokers or exsmokers with a smoking history of <5 pack-years.

Table I. Subject demographics

Design 

This was a single-dose, randomized, double-blind, placebo-controlled, multicenter, 5-way, crossover study. The study was approved by the ethics research board of the respective institutions, and signed informed consent was obtained from all subjects. After an initial screening visit, subjects entered a screening period of 1 to 2 weeks to ensure clinical stability. This meant absence of daily symptoms, less than daily rescue β₂-agonist use, and stable lung function. Eligible subjects were randomized into the treatment portion of the trial, in which they would receive BI 1744 (2, 5, 10, and 20 μg) and placebo in a randomized sequence, determined by simple random assignment to 1 of the 5 possible treatment sequences using a block size of 5. Each treatment period consisted of 2 study days with a washout of 14 to 21 days between periods. At each treatment period, the study medication was administered in the morning after a predose 12-lead electrocardiograph (ECG), vital signs (blood pressure, pulse rate), laboratory blood testing, and pulmonary function measurements that were required to be within 15% of visit 1 values.

Methacholine inhalation challenges were conducted at 30 minutes, 4 hours, 8 hours, 24 hours, and 32 hours postdosing. The primary endpoint was measurement of methacholine PC₂₀ obtained at 24 hours. Secondary endpoints were measurements of methacholine PC₂₀ obtained at 30 minutes and 4, 8, and 32 hours after trial medication. Additional observations on test days included adverse events, use of concomitant medication, and need for test day rescue medication (salbutamol metered dose inhaler). Twelve-lead ECG recordings, vital sign measurements, physical examination, and blood laboratory evaluation were performed at the beginning of participation in the study and after completion of the randomized treatment period, or when a patient discontinued the study prematurely. A serum pregnancy test was performed on all females of child-bearing potential at the first visit, and urine pregnancy tests were performed before trial medication administration.

Laboratory procedures 

BI 1744 was delivered as an aqueous solution by inhalation via a Respimat Inhaler (Boehringer Ingelheim Inc), which is a multidose, handheld nebulizer.¹³ Each dose was self-administered under direct supervision by oral inhalation of 2 puffs from 2 different inhalers. The different inhalers were needed to ensure correct dosing because the unit strength for BI 1744 in the Respimat Inhaler is 0.5 μg/actuation, 2.5 μg/actuation, or 10 μg/actuation. On the basis of the preclinical pharmacology of BI 1744, the therapeutic dose range for BI 1744 inhaled via the Respimat Inhaler was estimated to be 3 to 7 μg. Therefore, a dose range of 2 μg to 20 μg was chosen for an evaluation of the dose-response of BI 1744; at least 2 doses were expected to be on the plateau of the dose-response curve, whereas the lowest dose of 2 μg was expected to be minimally effective.

Lung function measurements were performed by using a spirometer that was calibrated by study staff on all study days. Equipment and techniques were required to conform to American Thoracic Society criteria.¹⁴ Pulmonary function tests (PFTs) were performed with the subject in a seated position, having abstained from short-acting inhaled β₂-agonists for at least 8 hours. Also, caffeine-containing beverages were not allowed from midnight of the day of the testing and during all measurements after dosing. For all baseline FEV₁ measurements, the best of 3 efforts was defined as the highest acceptable FEV₁ obtained on any of 3 blows meeting the American Thoracic Society criteria.

The methacholine inhalation challenge was performed as described by Cockcroft et al,¹⁵ using tidal breathing, from a Wright nebulizer. Methacholine doses ranged from 0.03 mg/mL to 256 mg/mL. The test was terminated when a fall in FEV₁ of at least 20% of the baseline value occurred, and the methacholine PC₂₀ was calculated. Log2 transformation was used for each PC₂₀ value before any analysis was performed or individual differences calculated. When the methacholine challenge was stopped before achieving a 20% fall in FEV₁, when the highest dose of inhaled methacholine was reached, the PC₂₀FEV₁ was estimated using log-linear extrapolation from the FEV₁ values at the last 2 methacholine concentrations. The values were then antilogged for the purposes of graphical representation and description of results.

Statistical analysis 

On the basis of previous data on the reproducibility of methacholine PC₂₀ measurements,¹⁶ it was calculated that 25 evaluable subjects would provide 95% power to detect a difference of 1.0 doubling dose between each dose of BI 1744 and placebo, assuming an SD of 1.25 doubling doses. The primary endpoint was the methacholine PC₂₀ value at 24 hours after dosing. The statistical model used a crossover analysis of variance testing center, subjects within center, treatment, and period as fixed effects for all variables. An intention-to-treat analysis was conducted on the data set. The statistical comparisons of the responses to the different doses of BI 1174 were exploratory and have not been adjusted for multiple comparisons. All tests of hypotheses were 1-sided with statistical significance defined as P ≤ .025.

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Results 

A total of 48 subjects were screened for the study, with 31 subjects randomized and treated. Five subjects discontinued the study prematurely: 1 because of worsening of asthma and 4 for administrative reasons, which included lack of compliance with the study protocol and withdrawal of consent. Therefore, 26 subjects completed all arms of the study.

BI 1744 increased the methacholine PC₂₀ in a dose-dependent and time-dependent fashion. The mean (geometric SEM) methacholine PC₂₀ 24 hours after dosing with placebo was 1.73 (1.13) mg/mL, which increased after 2 μg to 3.86 (1.14) mg/mL, after 5 μg to 5.67 (1.14) mg/mL, after 10 μg to 9.42 (1.13) mg/mL, and after 20 μg to 13.63 (1.14) mg/mL (all P < .0001 vs placebo; Fig 1, Table II). There were also significant differences between doses in the increases in the methacholine PC₂₀ values at 24 hours after dosing (Table III).

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• Fig 1. 

  Geometric mean methacholine PC₂₀ values over a period of 32 hours after inhaled dosing with single doses of BI 1744 ranging from 2 μg to 20 μg or placebo. The methacholine PC₂₀ values are significantly different for all doses compared with placebo at all time points.

Table II. FEV₁ values after dosing but before challenge and methacholine PC₂₀ at each time point for placebo and each dose of BI 1744

The placebo FEV₁ values are absolute values in liters (mean ± SEM). The FEV₁ values after dosing are the absolute differences in liters from placebo (mean ± SEM). Methacholine PC₂₀: mean (geometric SEM).

Table III. Dose-dependent effect of BI 1744 on methacholine PC₂₀ at 24 hours after dosing

The methacholine PC₂₀ also significantly increased at all time-points for all doses of BI 1744 (all doses P < .0001 vs placebo). The maximal effects were observed after dosing with the 20-μg dose, where the methacholine PC₂₀ was 24.54 (1.13) mg/mL at 30 minutes, 27.59 (1.16) mg/mL at 4 hours, 27.78 (1.16) mg/mL at 8 hours, and 12.17 (1.15) mg/mL at 32 hours (Fig 1, Table II).

All doses of BI 1744 significantly increased the prechallenge FEV₁ at all time points. The mean FEV₁ value was 3.48 L 30 minutes after placebo but before methacholine challenge, and this increased after the 20-μg dose to 3.78 at 30 minutes after dosing (P < .0001). The mean FEV₁ after the 20-μg dose remained at 3.75 L at 32 hours after dosing (P < .0001; Fig 2, Table II).

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• Fig 2. 

  FEV₁ measurements made before each methacholine inhalation challenge over a period of 32 hours after inhaled dosing with single doses of BI 1744 ranging from 2 μg to 20 μg or placebo. The FEV₁ values are significantly different for all doses compared with placebo at all time points.

The incidence of adverse events (AEs) in subjects in all treatment groups was similar to the subjects in the placebo group. An AE was experienced by 27.6% of subjects on placebo, 10.7% on the 2-μg dose, 7.1% on the 5-μg dose, 6.7% on the 10-μg dose, and 20.7% on the 20-μg dose. The most frequently reported AEs during treatment periods were headache and cough. Transient cough was experienced by 1 subject on placebo and on each of the doses of BI 1744, except for the 20-μg dose, where it occurred in 2 subjects. Most AEs were mild to moderate in intensity, with only 1 severe event (influenza) in the 20-μg BI 1744 treatment group. There were no serious AEs throughout the study. Also, there were no obvious clinically relevant changes in systolic or diastolic blood pressure or in heart rate at any dose of BI 1744 at any time during the 32-hour period of observation.

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Discussion 

This study has demonstrated that BI 1744 is a long-acting inhaled β₂-agonist with a duration of bronchodilation and functional antagonism of at least 32 hours for all of the doses studied. The medication was well tolerated, with minimal side effects, even those usually experienced after administration of inhaled β₂-agonists.

Methacholine inhalation challenge has been used previously to measure the magnitude and duration of functional antagonism of inhaled β₂-agonists, which is their ability to protect against induced bronchoconstriction. Drugs that are considered to be short-acting inhaled β₂-agonists such as albuterol or terbutaline are potent functional antagonists that partially protect asthmatic airways against stimuli such as exercise² or cold air hyperventilation.³ They can also increase methacholine PC₂₀, but this effect lasts less than 4 hours.¹¹ By contrast, both of the LABAs currently available for the treatment of asthma, formoterol and salmeterol, increase the methacholine PC₂₀ for at least 12 hours¹¹, ¹⁷ and as long as 24 hours.¹⁸ There is no previously described duration of functional antagonism with an inhaled β₂-agonist beyond 24 hours. This study also indicates that if challenge tests are performed on patients with asthma treated with BI 1744, a prolonged washout needs to be undertaken to avoid the functional antagonism that the LABA provides.

The use of clinical models of functional antagonism or bronchoprotection for investigation of inhaled β-agonists has several advantages over the more conventional duration of bronchodilation method. First, it is increasingly difficult to find and study individuals with significant resting bronchoconstriction, a feature that signifies unacceptable control by today's treatment standards.¹ The functional antagonism model allows the study of patients with asthma with normal spirometry and with no significant resting bronchodilator response. In addition, the bronchodilation model is a closed-end scale because there is limited room for improvement; consequently, it is often difficult to demonstrate a dose-response effect. By contrast, the functional antagonist model is open-ended and therefore much more likely to allow demonstration of a dose-response, as was shown in the current study. Most importantly, the clinical duration of β₂-agonist efficacy is likely more closely related to the duration of the bronchoprotective effect rather the duration of bronchodilation as shown in asthmatic studies in a laboratory.¹⁹ Bronchoprotection duration of a standard dose of albuterol is about 3 hours,¹⁹ compared with up to 6 hours for bronchodilation.²⁰

The maximum degree of protection afforded by BI 1744 at the higher of the inhaled doses (10 μg and 20 μg) was 12-fold and 19-fold, respectively, and this was achieved within 30 minutes of dosing and remained unchanged for up to 8 hours. The effect of 20 μg BI 1744 was similar in magnitude to that achieved after single dosing with formoterol 24 μg (which was a 20-fold increase in the methacholine PC₂₀, 4 hours after dosing) in a similar subject population.¹¹ However, the magnitude of protection by formoterol had decreased to a 10-fold increase by 8 hours and 8-fold by 12 hours.¹¹ There was also a dose-dependent effect of treatment with BI 1744, with the lower 2 doses (2 μg and 5 μg) achieving a maximal degree of protection of 4-fold and 6-fold respectively, and this benefit also persisted for up to 32 hours after dosing.

When multiple inhalation challenge tests are performed on the same day, the results may be influenced by the development of tachyphylaxis to methacholine, residual bronchoconstriction from an earlier test, or diurnal variation in airway responsiveness.²¹ Tachyphylaxis to repeated histamine inhalation tests occurs in subjects with asthma,²² whereas tachyphylaxis to methacholine occurs only in normal subjects.²³ Also, the methacholine PC₂₀ after placebo treatment did not significantly change over the 32 hours of measurement in the current study, indicating that these concerns do not materially affect the results obtained.

The subjects selected for this study were all patients with mild, intermittent asthma not needing regular treatment. The enrollment criteria required a prebronchodilator FEV₁ measurement of >80% predicted normal, and the mean baseline FEV₁ for the group was 97% predicted normal. It was not expected that BI 1744 would provide bronchodilation in this group of subjects; however, all doses of BI 1744 did produce significant bronchodilation, and this persisted for up to 32 hours after dosing for all doses administered (Fig 2, Table II). The magnitude of the effect was small, with a maximum of approximately 300 mL for the 20-μg dose, but this is likely because the starting FEV₁ was close to normal. The small increase in prechallenge FEV₁ may account for a slight effect on the methacholine PC₂₀ measurements. However, there was no dose-dependent effect between doses of BI 1744 over the first 8 hours in the degree of bronchodilation, but substantial differences in the methacholine PC₂₀ values, suggesting that this effect did not account for the functional antagonist effect achieved by BI 1744.

Tolerance has been consistently shown to develop to the functional antagonism effect of both short-acting and long-acting inhaled β₂-agonists with regular use.²⁴, ²⁵, ²⁶, ²⁷ Interestingly, it has been much more difficult to demonstrate tolerance to the bronchodilator effects of inhaled β₂-agonists, even when studied over a period of 1 year in patients with moderate-to-severe asthma.⁴ The current study administered only single doses of BI 1744, each dose separated by at least 1 week, so it is not possible to comment on the degree of tolerance that may develop with regular use of BI 1744.

Inhaled β₂-agonists have characteristic unwanted effects, likely mediated by the nonselective effects of the agonist on β₁-receptors on cardiac and skeletal muscle.²⁸ No changes in heart rate or blood pressure were seen during treatment with any of the doses of BI 1744, nor was tremor reported; however, only single doses were administered. By contrast, in a study of similar design with single doses of the LABA formoterol,¹¹ tremor was recorded by most subjects, and significant increases in systolic blood pressure were documented at both of the doses studied.

In summary, BI 1744 has a sustained protection against methacholine-induced bronchoconstriction of at least 32 hours. All doses studied were significantly better than placebo at all time points; furthermore, a dose-dependent effect was demonstrated. BI 1744 also demonstrated sustained bronchodilation, again lasting at least 32 hours, for all doses studied, although the magnitude was small as the starting FEV₁ in these subjects was close to normal.

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M.F. is a BC Lung CIHR/Scientist and a Michael Smith Foundation for Health Research Distinguished Scholar.

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