Rate of exposure to theophylline-drug interactions

Many drugs have been shown to interact adversely with theophylline, including ciprofloxacin, verapamil, and cimetidine. These drug interactions may have serious results such as seizures, circulatory failure, and respiratory arrest, which may require hospitalization. Thus interactions should be prevented. This study was conducted to help understand the degree to which patients taking theophylline are exposed to the potential risks of theophylline toxicity. Detailed diagnostic, demographic, and health care utilization data were obtained from the Pennsylvania Medicaid Management Information System computer files on patients who filled at least one prescription for any theophylline-containing drug between October 1, 1991, and December 31, 1992, and whose prescriptions for theophylline extended into 1992. The outcome measure of interest in this analysis was the rate at which patients were exposed to potential theophylline interactions, defined as the percentage of time that a patient was taking theophylline that he or she was also prescribed another drug known to interact adversely with theophylline. A total of 17,933 patients met the study criteria. On average, patients included in the analysis received theophylline for 121.3 out of 365 days in 1992. When the theophylline-interacting drugs were examined in the aggregate, 6619 patients (36.9%) were prescribed at least one of the drugs concomitantly with theophylline, for an average duration of 70.4 days of exposure. The overall rate of exposure to potential theophylline-drug interactions was 17.8%. These findings indicate that patients taking theophylline are exposed to adversely interacting drugs a significant proportion of the time that they are receiving theophylline. Clinicians should be made aware of this risk so that they may prescribe safer treatments that avoid this problem.