Plasma theophylline concentrations, six minute walking distances, and breathlessness in patients with chronic airflow obstruction.

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Abstract
Twenty patients with chronic bronchitis were given incremental dosages of a new slow release preparation of theophylline and observed for its effect on lung function and exercise tolerance. Measurements were made subjectively by using visual analogue scales and objectively using six minute walking distances and spirometry. The study was placebo controlled and had a double blind randomised design. In the dosages used (200, 400, 600, and 800 mg) theophylline produced no significant improvement in forced expiratory volume in one second or forced vital capacity, and there was no overall improvement in peak expiratory flow rate. Similarly, neither effort tolerance nor degree of breathlessness appeared to be influenced by the drug, even when unacceptably high dosages were used. By contrast, placebo yielded a 7% increase in the six minute walking distance. From these results it seems difficult to justify the routine, indiscriminate use of theophylline for chronic bronchitis.