Theophylline metabolism in acute asthma with MxA-indicated viral infection

Background: Although viral infection might alter theophylline metabolism in acute asthma, there are some difficulties in detecting infection due to various kinds of viruses in a clinical setting. Methods: To evaluate the usefulness of assessment of MxA protein in acute asthma exacerbated by viral infection, MxA protein expression in lymphocytes was assayed by flow cytometric analysis in whole peripheral blood in 21 children (aged 0-6 years) receiving continuous theophylline infusion for management of asthma attack. Serum theophylline levels were measured at 24 and 72 h after initiating theophylline infusion. Results: At the beginning of theophylline infusion, 11 children had increased expression of MxA protein, indicating viral infected states. After 24 h continuous infusion, there were no differences in theophylline levels between MxA-negative and MxA-positive groups. After 72 h infusion, the mean theophylline level of MxA-positive children was significantly higher than that of MxA-negative children (9.7 ± 2.2 μg/mL vs 7.3 ± 1.6 μg/mL). The ratio of theophylline clearance at 72 h to that at 24 h in the MxA-positive group was significantly lower than that of the MxA-negative group (1.1 ± 0.2 vs 1.4 ± 0.1). Conclusions: Viral infection appeared to affect theophylline metabolism. Flow cytometric assay of lymphoid MxA protein expression in whole blood is an easy and useful method of evaluating viral infection in acute asthma exacerbation.