Dose equivalence and bronchoprotective effects of salmeterol and salbutamol in asthma

A Dose-Response Study Examining the Use of Methacholine Challenge to Demonstrate Local Therapeutic Equivalence of the Salmeterol Component of Generic Inhaled Fluticasone Propionate/Salmeterol Combination Products

Background: Asthma is widely treated using inhaled corticosteroid/long-acting beta agonist (LABA) combinations, for example, fluticasone propionate/salmeterol (FPS) dry powder inhaler, marketed as Advair^® Diskus^®. Some regulators require generics to demonstrate local (lung) therapeutic equivalence (LTE) for each component of the FPS reference, ideally with a dose-response within the approved FPS dose range. We sought to develop a methacholine challenge (MeCh) LTE methodology for assessing the LABA (salmeterol) component of FPS. Methods: Forty-six patients with asthma received single doses of albuterol (active control; 90 or 180 μg), FPS (100/50 or 200/100 μg), and placebo on 5 separate study days. Spirometry and MeCh were performed 1, 6, and 10 hours after study drug inhalation. Primary endpoint was provocative concentration of methacholine producing a 20% fall in forced expiratory volume in 1 second (PC₂₀). Study entry required screening PC₂₀ ≤8 mg/mL, with a greater than fourfold increase (and PC₂₀ ≤128 mg/mL) after 180 μg albuterol. Results: Both albuterol (90 and 180 μg) and FPS (100/50 and 200/100 μg) significantly increased PC₂₀ compared with placebo (sustained 6 and 10 hours postdose with FPS but not albuterol). The dose-response slopes (95% confidence interval) estimated 1 hour after treatment were 0.374 (-0.068 to 0.815) and 0.310 (-0.135 to 0.754) between low and high doses of albuterol and FPS, respectively, both nonsignificant. Slopes were shallower than those available in the literature for albuterol and formoterol, but similar to those for salmeterol. Conclusions: These data confirm that the bronchoprotective effect of FPS lasts longer than that of albuterol. The shallow dose-response slope we observed for albuterol is contrary to previous reports, probably due to the measurement of PC₂₀ beginning at 1 hour postdose. The results suggest that use of MeCh to assess LTE for salmeterol formulations may be more difficult to accomplish than it is for albuterol and formoterol products.

Effect of Study Design on Sample Size in Studies Intended to Evaluate Bioequivalence of Inhaled Short-Acting β-Agonist Formulations

Pharmacodynamic studies that use methacholine challenge to assess bioequivalence of generic and innovator albuterol formulations are generally designed per published Food and Drug Administration guidance, with 3 reference doses and 1 test dose (3‐by‐1 design). These studies are challenging and expensive to conduct, typically requiring large sample sizes. We proposed 14 modified study designs as alternatives to the Food and Drug Administration–recommended 3‐by‐1 design, hypothesizing that adding reference and/or test doses would reduce sample size and cost. We used Monte Carlo simulation to estimate sample size. Simulation inputs were selected based on published studies and our own experience with this type of trial. We also estimated effects of these modified study designs on study cost. Most of these altered designs reduced sample size and cost relative to the 3‐by‐1 design, some decreasing cost by more than 40%. The most effective single study dose to add was 180 μg of test formulation, which resulted in an estimated 30% relative cost reduction. Adding a single test dose of 90 μg was less effective, producing only a 13% cost reduction. Adding a lone reference dose of either 180, 270, or 360 μg yielded little benefit (less than 10% cost reduction), whereas adding 720 μg resulted in a 19% cost reduction. Of the 14 study design modifications we evaluated, the most effective was addition of both a 90‐μg test dose and a 720‐μg reference dose (42% cost reduction). Combining a 180‐μg test dose and a 720‐μg reference dose produced an estimated 36% cost reduction.

Methacholine challenge tests to demonstrate therapeutic equivalence of terbutaline sulfate via different Turbuhaler® devices in patients with mild to moderate asthma: Appraisal of a four-way crossover design

BACKGROUND/OBJECTIVE

To demonstrate therapeutic equivalence of terbutaline via two different Turbuhaler^® devices by evaluating its protective effect against methacholine-induced bronchoconstriction in stable asthma.

METHODS

In this double-blind, double-dummy, multicentre, single-dose, 4-way crossover study, patients with stable mild-to-moderate asthma (FEV₁ ≥80% predicted) were randomised to 0.5 or 1.5 mg terbutaline via either Turbuhaler^® M2 or Turbuhaler^® M3 followed by a methacholine challenge test. The primary outcome variable was the concentration of methacholine causing a 20% drop in FEV₁ (PC₂₀). Patients had a PC₂₀ methacholine <8 mg/mL that was reproducible after 2 weeks, and a stable baseline FEV₁ at all visits (90-110% of enrolment value).

RESULTS

60 patients (mean age 31.1 years [range:18-64]; mean FEV₁ 92.1% predicted normal [78.4-120.6%]) were randomised to treatment; all completed the study. There was a clear dose-response for both devices. The within-device ratios (1.5 mg:0.5 mg) were 1.79 and 1.87 for Turbuhaler^® M3 and M2, respectively (both p < 0.001). The between-device ratios (M3:M2) were 0.92 (95% CI: 0.75-1.13) for 0.5 mg and 0.88 (95% CI 0.72-1.08) for 1.5 mg. Both confidence intervals lie inside the interval 0.67-1.50, which was the pre-specified condition for equivalent effect.

CONCLUSIONS

Bronchoprotection using a standardised methacholine challenge model proved to be an effective design to elucidate therapeutic equivalence between devices in patients with mild-to-moderate asthma. The findings indicate that patients may switch from one type of Turbuhaler^® to the other without adjustment of therapy. Moreover, they show the robustness and utility of this study design and its suitability for investigating therapeutic equivalence.

EUDRACT NUMBER

2014-001457-16. CLINICALTRIALS.

GOV IDENTIFIER

NCT02322788.

Pharmacodynamic Studies to Demonstrate Bioequivalence of Oral Inhalation Products

In the session on "Pharmacodynamic studies to demonstrate efficacy and safety", presentations were made on methods of evaluating airway deposition of inhaled corticosteroids and bronchodilators, and systemic exposure indirectly using pharmacodynamic study designs. For inhaled corticosteroids, limitations of measuring exhaled nitric oxide and airway responsiveness to adenosine for anti-inflammatory effects were identified, whilst measurement of 18-h area under the cortisol concentration-time curve was recommended for determining equivalent systemic exposure. For bronchodilators, methacholine challenge was recommended as the most sensitive method of determining the relative amount of β-agonist or anti-muscarinic agent delivered to the airways. Whilst some agencies, such as the Food and Drug Administration (FDA), do not require measuring systemic effects when pharmacokinetic measurements are feasible, the European Medicines Agency requires measurement of heart rate and serum potassium, and some require serial electrocardiograms when bioequivalence is not established by pharmacokinetic (PK) studies. The Panel Discussion focused on whether PK would be the most sensitive marker of bioequivalence. Furthermore, there was much discussion about the FDA draft guidance for generic fluticasone propionate/salmeterol. The opinion was expressed that the study design is not capable of detecting a non-equivalent product and would require an unfeasibly large sample size.

Acute effects of higher than customary doses of salmeterol and salbutamol in patients with acute exacerbation of COPD

Worsening of underlying bronchospasm may be associated with acute exacerbations of chronic obstructive pulmonary disease (COPD). As airway obstruction becomes more severe, the therapeutic option is to add salbutamol, but not salmeterol, as needed to cause rapid relief of bronchospasm. Unfortunately the most effective dosage of beta2-agonists may increase above that recommended during acute exacerbations. In this study, we compared the acute effects of higher than customary doses of salmeterol and salbutamol in 20 patients with acute exacerbation of COPD. A dose-response curve to salmeterol pMDI, 25 microg/puff or salbutamol pMDI, 100 microg/puff, was constructed using 1, 1, and 2 puff' i.e., a total cumulative dose of 100 microg salmeterol or 400 microg salbutamol on 2 consecutive days. After baseline measurements, dose increments were given at 30-min intervals with measurements being made 25 min after each dose. Hear rate (HR) and pulse-oximetry (SpO2) measurements were then taken. Both salmeterol and salbutamol induced a larg and significant (P < 0.05) dose-dependent increase in FEV1 [mean differences from baseline (L) = after 100 microg salmeterol 0.174 (95% CI: 0.112 to 0.237); after 400 microg salbutamol: 0.165 (95% CI: 0.080 to 0.249)], in IC [mean differences from baseline (L) = after 100 microg salmeterol: 0.332 (95% CI: 0.165 to 0.499); after 400 microg salbutamol: 0.281 (95% CI: 0.107 to 0.456)] (Fig. 2), and in FVC mean differences from baseline (L) = after 100 microg salmeterol: 0.224 (95% CI: 0.117 to 0.331); after 400 microg salbutamol: 0.242 (95% CI: 0.090 to 0.395)]. There was no significant difference between the FEV1 values (P=0.418), the ICvalues (P=0.585), and the FVCvalue (P=0.610) after 100 microg salmeterol and 400 microg salbutamol. HR [mean differences from baseline (beats/min) = after 100 microg salmeterol: 3.15 (95% CI: -0.65 to 6.96); after 400 microg salbutamol: 2.30 (95% CI: -0.91 to 5.51)] and SpO2 [mean differences from baseline (%) = after 100 microg salmeterol: -0.20 (95% CI: -1.00 to 0.60); after 400 microg salbutamol: -0.11 (95% CI: -1.00 to 0.79)] did not change significantly from baseline (P > 0.05). These data indicate that salmeterol is effective and safe in the treatment of acute exacerbation of COPD and support its use in this clinical condition.

Salmeterol 100 microg: an analysis of its tolerability in single- and chronic-dose studies

BACKGROUND

A combination product containing fluticasone propionate 100 or 250 microg and salmeterol 50 microg has recently been made available in the United States. Some patients, if previously instructed to double their inhaled corticosteroids, may double this product, inadvertently receiving higher doses of salmeterol, potentially causing systemic beta2-agonist-related effects.

OBJECTIVES

To examine the systemic effects of single and chronic doses of salmeterol 100 microg.

METHODS

Forty-four studies including a salmeterol 100 microg treatment arm were identified. Data on predictable systemic effects were available in 10 single-dose and 9 chronic-dose studies lasting more than 7 days, in patients with asthma (6 adult, 2 pediatric) or chronic obstructive pulmonary disease (1 study), which were included in a weighted, pooled analysis.

RESULTS

Single 100-microg dose studies: mean change from baseline in heart rate was +2.3 beats per minute and systolic blood pressure +0.4 mm Hg. Tremor and palpitations were reported in 5.7% and 2.8%. Other systemic effects included a decrease in serum potassium for 3 subjects (2.1%); an increase in serum glucose, 1 subject (0.7%); and electrocardiographic (ECG) events, 24 cases (17.0%). Twenty-three of these were from one crossover study which reported 27 ECG events after placebo. Chronic dose studies (salmeterol 100 microg): mean change in heart rate and systolic blood pressure were +1.8 beats per minute and -0.2 mm Hg. Tremor and palpitations were reported in 5.6% and 1.7% of 1,504 patients. Thirteen recorded a decrease in serum potassium (0.9%) and 5 an increase in serum glucose (0.3%). Nine patients had ECG events (0.6%). Eight of these were "arrhythmia" from one study, which also reported 12 events before treatment.

CONCLUSIONS

The mean systemic effects of salmeterol 100 microg are small and of doubtful clinical relevance. Patients (and their caregivers) can be reassured that inadvertently taking double doses of the new combination product are unlikely to affect them adversely.

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

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