EFFECT OF ORAL THEOPHYLLINE ON RESTING ENERGY-EXPENDITURE IN NORMAL VOLUNTEERS

Background - The aim of this study was to investigate the contribution of regular treatment with oral theophylline to the increase in restin g oxygen consumption observed in patients with chronic airflow limitat ion who are receiving bronchodilator therapy. Methods - Resting oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured in 10 normal subjects (six men, age 21-48 years, weight 50-85 kg) befo re and after 11 days of treatment with either placebo or theophylline in a double blind manner, in twice daily oral doses ensuring trough se rum concentrations between 8.4 and 13.5 mg/l. An open canopy method wa s used to measure VO2 and VCO2 and in all test conditions this was ext ended for 60 minutes after an inhalation of 800 mu g of salbutamol sup erimposed on the background placebo or theophylline treatment. Results - Resting VO2 and heart rate were increased during theophylline treat ment compared with placebo by 6.5% and 8.4% respectively. Salbutamol i nhalation transiently increased VO2, VCO2, and heart rate in all tests but this was not modified by background theophylline treatment. Concl usion - Oral theophylline treatment causes a sustained increase in res ting oxygen consumption and heart rate but does not modify the metabol ic response to acutely inhaled salbutamol.