Theophylline protein binding in humans.

Theophylline protein binding was 58-82% in serum from six normal adults and 42 asthmatic patients, 1-25 years old, who were given 5 mg of theophylline/kg. The binding range was greatest in young patients, but the proportion of protein-bound drug did not correlate with age. Theophylline protein binding was higher than previously reported. The effect of binding should be considered in patients who do not have optimal bronchodilation from theophylline despite total serum theophylline concentrations of 10-20 microgram/ml.