Incidence and cost of hospital admissions secondary to drug interactions involving theophylline

OBJECTIVE: To determine the incidence and cost of hospital admissions for theophylline toxicity, which occurred as a result of the concurrent use of one of the following medications: cimetidine, erythromycin, or ciprofloxacin. DESIGN: Retrospective chart review (18 months, between June 1989 and November 1990). SETTING: A Department of Veterans Affairs Medical Center. PARTICIPANTS: All patients who were receiving theophylline chronically (913 patients) and also had a prescription for cimetidine (124 patients with 140 treatment courses), erythromycin (66 patients with 93 treatment courses), or ciprofloxacin (39 patients with 59 treatment courses) dispensed. INTERVENTIONS: Each patient's medical record was reviewed to identify hospital admissions within 30 days following the dispensing of the interacting drug. MAIN OUTCOME MEASURES: Admissions were considered to be related to theophylline toxicity if appropriate signs and symptoms were present and the theophylline concentration was above 20 micrograms/mL or had increased significantly from the concentration obtained prior to introduction of the interacting drug. RESULTS: One patient who received cimetidine and one who received ciprofloxacin were admitted for theophylline toxicity (2 of 292 potential interactions, 0.81 percent). Admissions were for 16 and 13 days, respectively, and total costs for the two admissions were $12,864.22 or $44.00, respectively, per potential interaction. The entire admission was not for theophylline toxicity; it appeared that iatrogenic factors contributed to the duration. CONCLUSIONS: The incidence of hospital admissions secondary to theophylline drug interactions with cimetidine, ciprofloxacin, or erythromycin is low, but the admissions represent considerable expense, even when distributed among all patients at risk for the interactions.