RATE OF EXPOSURE TO THEOPHYLLINE DRUG-INTERACTIONS

Many drugs have been shown to interact adversely with theophylline, in cluding ciprofloxacin, verapamil, and cimetidine. These drug interacti ons may have serious results such as seizures, circulatory failure, an d respiratory arrest, which may require hospitalization. Thus interact ions should be prevented. This study was conducted to help understand the degree to which patients taking theophylline are exposed to the po tential risks of theophylline toxicity. Detailed diagnostic, demograph ic, and health care utilization data were obtained from the Pennsylvan ia Medicaid Management Information System computer files on patients w ho filled at least one prescription for any theophylline-containing dr ug between October 1, 1991, and December 31, 1992, and whose prescript ions for theophylline extended into 1999. The outcome measure of inter est in this analysis was the rate at which patients were exposed to po tential theophylline interactions, defined as the percentage of time t hat a patient was taking theophylline that he or she was also prescrib ed another drug known to interact adversely with theophylline. A total of 17,933 patients met the study criteria. On average, patients inclu ded in the analysis received theophylline for 121.3 out of 365 days in 1992. When the theophylline-interacting drugs were examined in the ag gregate, 6619 patients (36.9%) were prescribed at least one of the dru gs concomitantly with theophylline, for an average duration of 70.4 da ys of exposure. The overall rate of exposure to potential theophylline -drug interactions was 17.8%. These findings indicate that patients ta king theophylline are exposed to adversely interacting drugs a signifi cant proportion of the time that they are receiving theophylline. Clin icians should be made aware of this risk so that they may prescribe sa fer treatments that avoid this problem.