EFFECT OF INCREASING DOSES OF BETA-AGONISTS ON SPIROMETRIC PARAMETERS, EXERCISE CAPACITY, AND QUALITY-OF-LIFE IN PATIENTS WITH CHRONIC AIR-FLOW LIMITATION

Background - A study was undertaken to determine the impact of differe nt doses of inhaled terbutaline on peak flow rates, spirometric parame ters, functional exercise capacity, and quality of life in patients wi th chronic airflow limitation. Methods - A double blind, randomised, p lacebo controlled, multiple crossover trial was conducted with treatme nt periods of one week. Patients with a clinical diagnosis of chronic airflow limitation and FEV(1) below 70% predicted after administration of bronchodilator were recruited from secondary care respiratory prac tices, and the effect of 500, 1000, and 1500 mu g inhaled terbutaline four times daily on spirometric parameters (FEV(1), FVC), maximum insp iratory pressures, six minute walking distance, and health-related qua lity of life (Chronic Respiratory Disease Questionnaire, Quality of We ll Being, Standard Gamble) was measured. Results - Twenty five patient s completed the trial. Peak flow rates and FEV, showed statistically s ignificant but clinically trivial improvement on the higher drug doses . Results of maximum inspiratory pressure measurements, walk test dist ance, and quality of life measures showed minimal differences on the d ifferent dosages, and none of the differences approached conventional statistical significance, Conclusions - Regular use of beta agonists i n doses higher than two puffs four times a day is very unlikely to pro vide additional functional or symptomatic benefit to patients with chr onic airflow limitation.