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  • Title: Methacholine challenge as a clinical bioassay of pulmonary delivery of a long-acting β₂-adrenergic agonist.
    Author: Prabhakaran S, Shuster J, Ahrens R, Hendeles L.
    Journal: Pharmacotherapy; 2011 May; 31(5):449-57. PubMed ID: 21923426.
    Abstract:
    STUDY OBJECTIVE: To determine whether the methacholine challenge method used for albuterol can be applied to assess long-acting β2-adrenergic agonist (LABA) bioequivalence, which would require a sufficiently steep dose-response curve. DESIGN: Prospective, unblinded, randomized, 2-way crossover study. SETTING: University medical center clinical research laboratory. PATIENTS: Ten adults, aged 21-58 years, with mild asthma (forced expiratory volume in 1 sec [FEV(1)] ≥ 70% predicted) and a baseline provocational concentration of methacholine required to decrease FEV(1) by 20% (PC(20)) of 4 mg/ml or less completed the study. INTERVENTION: Patients were randomized to receive a single dose of either 12 or 24 μg of formoterol delivered by a dry powder inhaler; 3-7 days later, at the same time of day, they received the other dose. MEASUREMENTS AND MAIN RESULTS: The FEV(1) was measured before and 1 hour after dosing, followed by performance of a methacholine challenge. Statistical analysis was performed by the 2-sample regression method for crossover studies. The dose-response curve for bronchodilatation was flat; the mean ± SD increase in FEV(1) after formoterol 12 and 24 μg was 14 ± 5% and 14 ± 8%, respectively (p>0.05). In contrast, the geometric mean PC20 (95% confidence interval) was 7 mg/ml (2-22 mg/ml) after the 12-μg dose and 16 mg/ml (5-45 mg/ml) after the 24-μg dose (p<0.001). CONCLUSION: Bioassay by methacholine challenge will be useful for bioequivalence studies of LABAs. A sample of at least 28 patients will be required for formoterol when methacholine challenge is performed in an optimal manner. The sample size may differ for other LABAs.
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