Prolonged treatment with oral and inhaled tulobuterol does not induce airways tachyphlaxis

Beta 2-agonists have been shown to induce beta 2-adrenoceptor downregulation in vivo and in vitro. Whether this has any functional relevance remains unclear. Tulobuterol is a new synthetic beta 2-agonist with potent and prolonged bronchodilator activity when given by oral and inhaled routes. The effect of tulobuterol aerosol (400 micrograms q.i.d.) and tulobuterol tablets (2 mg b.i.d.) was studied in patients with chronic asthma and reversible airways obstruction in two separate trials. Tulobuterol produced significant bronchodilatation after the first and final dose over a 6-h period and the effects were comparable. The bronchodilator activity of tulobuterol given by inhalation and oral routes was not attenuated after 6 months of continuous treatment. There was significant improvement in symptom score and lung function measurements. Side effects, predominantly tremors, were observed at the start of treatment with tablet formulation but the incidence and severity of tremors decreased after 6 months. The changes in BP and pulse rate were not clinically significant. These results confirm the potent bronchodilator activity of tulobuterol and the lack of tachyphylaxis after prolonged treatment.