Cimetidine-theophylline interaction in patients with chronic obstructive airways disease.

The effect of cimetidine on the elimination of theophylline was studied in six patients with chronic obstructive airways disease, who were receiving maintenance therapy with theophylline. The administration of cimetidine resulted in a decrease of 25% in the interdose clearance of theophylline, which led to an increase in "steady-state" theophylline levels in five of the patients. Prescribers should be aware of this potential interaction and reduce theophylline dosage where appropriate.