[Long-term therapy with beta-2 mimetics: role of tachyphylaxis]

Long-term treatment with beta-2 agonists are said to induce bronchial adrenergic receptor desensitization. Tachyphylaxis is a pharmacological phenomenon that is usually observed with all the drugs and hormones that stimulate receptors. It plays a regulatory role in coupling-decoupling of hormone and receptor. In asthmatics, loss of bronchial responsiveness to a beta-2 adrenergic stimulation may differ from tachyphylaxis, since many factors contribute to the decrease of the response. Penetration of aerosol depends on bronchial obstruction, hypersecretion and inflammatory processes. Aerosols may induce bronchospasm that is related to propellants, the absorption of oral forms beta-2 agonists may exhibit large variation. Few longitudinal or transversal studies to detect the frequency tachyphylaxis in asthmatics have been done, but it has been shown recently that, in a population of asthmatics who were receiving long-term treatment, loss of bronchial response to beta-2 agonists, possibly related to receptor desensitization, was in a range of 10 to 15%.