Is routine monitoring of theophylline blood levels really effective?

Theophylline is widely used by patients with asthma and chronic obstructive pulmonary disease as a bronchodilator. The therapeutic range is relatively narrow: 10-20 mcg/ml. In a survey of 344 blood samples from 290 patients over a period of 12 months, 60% had levels lower than 10 mcg/ml, and only 28% were within the therapeutic range. This was especially the case among those using oral preparations. Our data raise several questions concerning the individualization of theophylline dosage, the effectiveness of its routine blood monitoring, and the implications of these results for ambulatory patients who are possibly being under treated.