Clinical trial efficacy: what does it really tell you?

The primary goal of most clinical trials is an evaluation of the efficacy of the drug being evaluated. Therefore, it is important to understand if study outcomes are a true reflection of a drug's "real-life" effectiveness. Clinical trials generally evaluate three types of outcomes: subjective, objective, and health-related. Clinical trials that use subjective measures as endpoints usually evaluate outcomes such as symptom scores, the need for rescue medication, and quality-of-life measures. The majority of clinical trials rely on objective measures to test the efficacy of asthma medications. These include lung function (peak expiratory flow rate, forced expiratory volume at one second [FEV1]), level of bronchial hyperresponsiveness (methacholine challenge or exercise challenge), and markers of inflammation (exhaled nitric oxide, sputum eosinophils, bronchoalveolar lavage, and bronchial biopsy). FEV1 remains the gold standard of efficacy measures; however, in pediatrics, where FEV1 values are often within the normal range, re-adjustment of what constitutes various levels of asthma severity should occur. Occasionally, studies will include an assessment of health outcomes, either as a primary or secondary measure, during the course of the study. Commonly measured health outcomes include a reduction in need for rescue systemic glucocorticoids, a reduction in the need for emergent asthma care, a reduction in asthma hospitalizations, and a reduction in asthma deaths. Studies designed to assess impact of treatment regimens on morbidity and mortality remain a high priority, as do studies designed to predict response to current asthma therapies.