Correlation of serum theophylline levels with inhibition of allergen and histamine-induced skin tests.

The purpose of this study was to determine if clinically effective serum levels of theophylline have an inhibitory effect on intradermal tests for allergic hypersensitivity. Intradermal testing using the threshold-dilution technique was performed in 9 patients, 7 of whom were sensitive to 2 antigens. Testing was performed over a 6-hour period after theophylline administration and compared with the control results. Inhibition of the end-point was demonstrated with 12 of 16 antigens tested associated with serum theophylline levels ranging from 7 to 20 microgram/ml. Marked inhibition of the intradermal tests, that might have clinical significance, only occurred with 4 antigens.