Clinical Pharmacology of Drugs Used In the Treatment of Asthma

CLINICAL PHARMACOLOGY OF DRUGS USED IN THE TREATMENT OF ASTHMA

Asthma is best thought of as a disease in two time domains. In the present domain, it is important for the distress it causes—cough, nocturnal awakenings, and shortness of breath that interferes with the ability to exercise or to pursue desired activities. For mild asthma, occasional inhalation of a bronchodilator may be all that is needed. For more severe asthma, treatment with a long-term controller, like an inhaled corticosteroid, is necessary to relieve symptoms and restore function. The second domain of asthma is the risk it presents of future events, such as exacerbations, or of progressive loss of pulmonary function. A patient’s satisfaction with his or her ability to control symptoms and maintain function by frequent use of an inhaled β₂ agonist does not mean that the risk of future events is also controlled. In fact, use of two or more canisters of an inhaled β agonist per month is a marker of increased risk of asthma fatality. The challenges of assessing severity and adjusting therapy for these two domains of asthma are different. For relief of distress in the present domain, the key information can be obtained by ask-ing specific questions about the frequency and severity of symp-toms, the frequency of use of an inhaled β₂ agonist for relief of symptoms, the frequency of nocturnal awakenings, and the ability to exercise. Estimating the risk for future exacerbations is more difficult. In general, patients with poorly controlled symptoms in the present have a heightened risk of exacerbations in the future, but some patients seem unaware of the severity of their underlying airflow obstruction (sometimes described as “poor perceivers”) and can be identified only by measurement of pulmonary func-tion, as by spirometry. Reductions in the FEV₁ correlate with heightened risk of attacks of asthma in the future. Other possible markers of heightened risk are unstable pulmonary function (large variations in FEV₁ from visit to visit, large change with broncho-dilator treatment), extreme bronchial reactivity, or high numbers of eosinophils in sputum or of nitric oxide in exhaled air. Assessment of these features may identify patients who need increases in therapy for protection against exacerbations.