Altered theophylline clearance during an influenza B outbreak

During the 1980 influenza B outbreak in King County, Washington, 11 children whose asthma had previously been controlled with a stable theophylline dose, developed theophylline toxicity on this same dose. Two had seizures, eight had nausea and vomiting, and three had headaches. All had clinical evidence of a febrile viral illness. The toxicity appeared to be related to decreased theophylline clearance, which gradually returned to preillness levels over a period of one to three months. Six of ten children had serologic evidence of influenza B, which is presumed to be the cause of the altered clearance. In children receiving chronic theophylline therapy, symptoms of vomiting, headaches, or seizures during a viral illness may be due to theophylline toxicity rather than the virus. Such patients should have an immediate serum theophylline determination, even if previous levels have been in the therapeutic range.