Relationship of serum theophylline concentrations to histamine-induced bronchospasm.

This study was performed in a randomized double-blind manner on 6 separate days in 10 asthmatic patients to investigate the effect of a sustained theophylline on baseline bronchial hyperreactivity to histamine in relation to the theophylline serum levels and the degree of bronchodilatation produced. No significant bronchodilatation was seen after theophylline administration at every time of evaluation. An improvement of PD20 values of histamine was observed after 4 h (p less than 0.05), 8 h (p less than 0.01) and 12 h (p less than 0.05) from theophylline administration versus respective PD20 values obtained with placebo at the same times. No significant correlation was found between serum theophylline levels and percentage change of PD20 values after drug administration (r = 0.250). We observed an improvement of PD20 mean values in relation to the maximal serum theophylline concentration but our study failed to correlate the degree of protection with serum concentration.