The mechanism of corticosteroids in treating asthma.

It would be difficult for physicians or allergists to imagine doing without corticosteroids in managing difficult cases of bronchial asthma. It is beyond any doubt that CS act on many sites to help reverse the pathologic process of bronchial asthma. Corticosteroids enhance the beta-adrenergic response to relieve the muscle spasm. They also act by reversing the mucosal edema, decreasing vascular permeability by vasoconstriction, and inhibiting the release of LTC4 and LTD4. Corticosteroids reduce the mucus secretion by inhibiting the release of secretagogue from macrophages. Corticosteroids inhibit the late phase reaction by inhibiting the inflammatory response and interfering with chemotaxis. This action may be due to the inhibition of LTB4 release. The eosinopenic effect of corticosteroids may help to prevent the cytotoxic effect of the major basic protein and other inflammatory mediators released from eosinophils. Corticosteroids have no effect on the immediate hypersensitivity reaction and have no direct role in bronchial reactivity. By blocking the late reaction, they prevent the increased airway reactivity observed with late bronchial reactions. The limitation of using corticosteroids are their side effects. They vary from tolerable to life threatening side effects. Each tissue in the body is a target for corticosteroids. The mechanism of adverse effects have been studied in extensive detail but many questions are yet to be answered. Alternate-day therapy and inhalation therapy are meant to minimize these side effects. The expansion of using inhaled steroid therapy and finding some inhaled preparations that have even less systemic side effects seems a reasonable approach to deal with severe asthma.