Use of serum theophylline level as a guide to optimum therapy in patients with chronic obstructive lung disease.

Blood and urine samples were collected simultaneously with measurements of pulmonary function at 2-hour intervals for 8 hours after oral administration of short-acting (SAT) and long-acting theophylline (LAT) preparations in 15 patients with stable chronic obstructive lung disease (COLD) on long-term maintenance theophylline therapy. The relationship between pulmonary function tests, serum theophylline level, plasma and urinary adenosine 3'5' cyclic monophosphate (cAMP) was examined. The highest forced expiratory volume in one second FEV1 was obtained with STL of 12.8 micrograms/ml +/- 5.21 SD and 9.14 micrograms/ml +/- 6.15 (P less than .05) after administration of SAT and LAT, respectively. A further increase in serum theophylline level (STL) offered no therapeutic benefit, and, in fact, was associated with a fall in FEV1 in many instances. Plasma or urinary cAMP measurements did not correlate with STL. STL at which the best pulmonary function is achieved is quite variable in patients with COLD on maintenance theophylline therapy, is frequently less than 10 micrograms/ml, and can be determined only by repeated measurements of pulmonary function at different STL. Therefore measurements of STL are of limited value in guiding treatment with theophylline.