Effect of danshen extract on pharmacokinetics of theophylline in healthy volunteers

Aims: To examine the potential effect of danshen extract on the pharmacokinetics of theophylline. Methods: In a sequential cross-over study with two phases, 12 volunteers took 100 mg theophylline on day 1 and day 15. From day 2 to day 15, volunteers received danshen extract tablets three times daily, four tablets each time for 14 days. On day 15, they received four danshen extract tablets with 100 mg theophylline. Plasma concentrations of theophylline were measured on days 1 and 15 periodically for 24 h. Results: The 90% confidence interval of C_max, t_1/2 and CL/F of theophylline with 14-day danshen extract tablets vs. without comedication were (101.42, 121.36) (84.57, 106.72) and (88.82, 105.72), respectively. The time to peak plasma theophylline concentration was unchanged by danshen (P > 0.05). The pharmacokinetics parameter of theophylline was unaffected by danshen extract. Conclusions: Danshen extract does not influence the metabolism of theophylline in healthy volunteers. Dose adjustment of theophylline thus may not be necessary in patients receiving concurrent therapy with danshen extract tablets.