Usefulness of the simultaneous determination of serum levels of theophylline and its metabolites in patients medicated with theophylline preparation

Objective: Measurement of the serum level of theophylline is essential for its proper use; however, it is difficult to infer the metabolic ability of individual patients by only the serum theophylline level and to decide the appropriate medication. In this study, we simultaneously measured serum theophylline and metabolite levels in patients treated with theophylline, and investigated their usefulness. Experimental: The subjects were asthma patients who visited the outpatient clinic of Respiratory Medicine, St Luke's International Hospital, between April and October 2003, and were medicated with sustained‐release theophylline tablets (Theodur®). The serum level of theophylline and its metabolites was measured by HPLC in patients who gave written consent. Results: A strong correlation was noted between the serum theophylline (TP) and 1,3‐dimethyluric acid (DMU) levels of 52 patients (r = 0.670), and DMU/TP was about 0.04. In a patient whose the DMU/TP was 0.216, it was recognized that metabolic ability was promoted due to a history of smoking. Discussion: In this study, it was shown that simultaneous measurement by HPLC of the serum level of theophylline and its metabolites and DMU/TP was useful to assess the metabolic ability of individual patients. Copyright © 2010 John Wiley & Sons, Ltd.