Pharmacokinetics of theophylline in hyperthyroid and hypothyroid patients with chronic obstructive pulmonary disease.

The pharmacokinetics of theophylline was investigated in five hyperthyroid, five hypothyroid, and five euthyroid patients, all with chronic obstructive pulmonary disease. Wide individual variability was found in theophylline kinetics, but the rate of elimination of theophylline was significantly higher in hyperthyroid, and lower in hypothyroid patients than in the euthyroid patients (kel = 0.155, 0.060 and 0.107 h-1, respectively). The values for clearance and volume of distribution were not consistently changed compared with those in the euthyroid group, although all the parameters except AUC were significantly different in hyperthyroid and hypothyroid patients. There was a positive correlation between both thyroxine and triiodothyronine serum concentrations and total body clearance of theophylline (r = 0.795 and r = 0.791, respectively). It is concluded that in spite of the wide interindividual variability and the relatively small differences in the pharmacokinetics of theophylline in thyroid dysfunction compared with the euthyroid status, these differences have to be considered in certain clinical situations, as they may require changes in the therapeutic regimen for administration of theophylline in hyperthyroid or hypothyroid patients.