Effect of slow-release oral aminophylline on circadian variation in airflow obstruction in asthmatics

The effect of an oral slow-release aminophylline preparation (Phyllocontin Continus tablets) in preventing early morning reduction in airway calibre was measured in two groups of asthmatic patients; Group I consisted of eight stable asthmatics whose main complaint was nocturnal wheeziness, and Group II comprised four severe asthmatics studied during the period of recovery from an acute exacerbation of asthma. In both groups the effect on one second forced expired volume (FEV1) of two 225 mg tablets of Phyllocontin was compared with that of two placebo tablets on two successive nights in a double-blind trial. On the nights when the placebo preparation was administered both groups of patients showed a marked fall in FEV1. Administration of the active aminophylline preparation prevented this reduction in airway calibre in the Group I patients but had no effect on the fall in FEV1 in the Group II patients. A possible explanation for the observed difference in response between the two groups may have been variation in bioavailability of aminophylline in the two clinical situations.