Nifedipine alters serum theophylline levels in asthmatic patients with hypertension.

The effect of nifedipine on serum theophylline levels in 13 female hypertensive patients having asthma on theophylline therapy has been investigated. Administration of a slow release theophylline product in a dose of 200 mg bidaily for 15 days provided a steady-state through serum theophylline concentration (11.2 +/- 2.7 micrograms/ml). After this period, 10 mg bidaily nifedipine was added to therapy and trough serum theophylline levels, pulmonary function tests and blood pressure measurements have been performed following 15 and 45 days of simultaneous use of theophylline and nifedipine. No change has been observed in serum theophylline level after 15 days of simultaneous use, however after 45 days, serum theophylline level was significantly lower (7.3 +/- 1 micrograms/ml). There were no changes in clinical responsiveness of either of these drugs.