Serum theophylline levels in adult asthmatics: comparison of oral sustained-release and microcrystalline preparations.

Serial serum theophylline levels were measured in 20 inpatient asthmatics given tablets of either microcrystalline or sustained-release theophylline. The sustained-release preparation gave serum levels which were more consistently within the therapeutic range with a significantly higher trough concentration. No increase in adverse effects was encountered.