EFFECT OF DRUG-INTERACTIONS ON OUTCOMES OF PATIENTS RECEIVING WARFARIN OR THEOPHYLLINE

The effect of drug interactions on costs and other outcomes for hospit alized patients receiving warfarin or theophylline was studied. Data w ere collected from medical records during a one-year period in two com munity teaching hospitals in Maryland. The data included demographic i nformation, the duration of study-drug therapy, the number of days spe nt in the intensive care unit, the length of stay (LOS) in the hospita l, the number of prothrombin-time tests and serum theophylline assays, and the test results. A multiple-regression procedure was used to com pare outcomes of patients who were prescribed specific drugs interacti ng with warfarin or theophylline with those of patients who were not. Among warfarin-treated patients, there was a significant difference in each outcome measure (LOS, number of laboratory tests, and test resul ts) between those who received an interacting drug and those who did n ot; mean LOS was 3.14 days longer in patients given an interacting dru g. No significant differences in outcome measures were observed betwee n the two groups of theophylline-treated patients. The cost of the inc reased LOS attributed to the presence of a drug interacting with warfa rin was estimated to range from $779 to $1005 per hospitalization. The cost of additional prothrombin-time tests was estimated at $19-$50. P atients who received warfarin and an interacting drug had an increased LOS, required more laboratory tests, and had longer prothrombin times than patients given warfarin alone; these differences probably led to higher costs.