Significance of the therapeutic range of serum theophylline concentration in the treatment of an attack of bronchial asthma.

The purpose of this study was to evaluate the accuracy of the recommended theophylline therapeutic range in the treatment of acute airway obstruction. Twenty seven patients (20 to 64 years) with acute asthma attack were given aminophylline intravenously to obtain a theophylline concentration between 10 and 20 micrograms/ml. Peak expiratory flow rates (PEFR) and serum theophylline concentrations were measured before and after aminophylline injection. When a marked improvement was not seen after aminophylline injection, the treatment was followed by inhalation of a beta-agonist and intravenously administered hydrocortisone. In order to clarify the relationship between theophylline efficacy at a therapeutic level and PEFR, as measured before aminophylline administration, the patients were classified into four groups. Group A (n = 7): asthma attack persisted regardless of treatment with aminophylline, beta-agonist and hydrocortisone, group B (n = 7): asthma attack improved by aminophylline, beta-agonist and hydrocortisone, group C (n = 6): asthma attack improved by both aminophylline and beta-agonist, group D (n = 7): asthma attack improved by intravenous aminophylline alone. The means (+/- S.E.) PEFR before aminophylline administration were 94.3 +/- 11.31/min in group A, 114.3 +/- 10.01/min in group B, 196.7 +/- 22.21/min in group C, and 220.0 +/- 12.51/min in group D, respectively. There were significant differences in PEFR between the A and C, A and D, B and C, and B and D groups. These findings suggest that theophylline efficacy is not expected in patients with low PEFR (less than 2001/min) at the time of treatment of an attack, even if a therapeutic theophylline concentration was obtained.