Impact of smoking on asthma therapy: a critical review of clinical evidence.

Airway inflammation is central to the pathophysiology of asthma, with treatment directed towards modification of this inflammation and its consequences. The relationship between cigarette smoking and airway inflammation is also well described, but relatively little data are available on the potential influence of smoking on asthmatic airway inflammation and its treatment. While cigarette smoking is common in people with asthma, with prevalence rates similar to the general population, studies in asthma have tended to concentrate on individuals who have never smoked. However, there is recent evidence that smoking may confer a degree of corticosteroid resistance in asthma, and this review examines the relationship between asthma and cigarette smoking, with particular reference to the impact of smoking on the response to treatment of asthma. Smoking has a number of known influences on drug activity and metabolism, but the mechanism underlying corticosteroid resistance in asthmatic smokers is not yet clear, although there are differences in the nature of the airway inflammation in individuals with asthma who smoke compared with nonsmoking asthmatic patients. Encouragingly, there is some evidence that smoking cessation may at least partially restore corticosteroid responsiveness in asthmatic ex-smokers. Smoking cessation measures must be given a high priority in individuals with asthma who smoke.