A National Survey on Prescribers' Knowledge of and Their Source of Drug-Drug Interaction Information-An Application of Item Response Theory

Abstract

OBJECTIVES: (1) To assess prescribers' ability to recognize clinically significant DDIs, (2) to examine demographic and practice factors that may be associated with prescribers' DDI knowledge, and (3) to evaluate prescribers' perceived usefulness of various DDI information sources.METHODS: This study used a mailed questionnaire sent to a national sample of prescribers based on their past history of DDI prescribing which was determined using data from a pharmacy benefit manager covering over 50 million lives. The survey questionnaire included 14 drug-drug pairs that tested prescribers' ability to recognize clinically important DDIs and five 5-point Likert scale-type questions that assessed prescribers' perceived usefulness of DDI information provided by various sources. Demographic and practice characteristics were collected as well. Rasch analysis was used to evaluate the knowledge and usefulness questions.RESULTS: Completed questionnaires were obtained from 950 prescribers (overall response rate: 7.9%). The number of drug pairs correctly classified by the prescribers ranged from zero to thirteen, with a mean of 6 pairs (42.7%). The percentage of prescribers who correctly classified specific drug pairs ranged from 18.2% for warfarin-cimetidine to 81.2% for acetaminophen with codeine-amoxicillin. Half of the drug pair questions were answered "not sure" by over one-third of the respondents; among which, two were contraindicated. Rasch analysis of knowledge and usefulness questions revealed satisfactory model-data fit and person reliability of 0.72 and 0.61, respectively. A multiple regression analysis revealed that specialists were less likely to correctly identify interactions as compared to prescribers who were generalists. Other important predictors of DDI knowledge included the experience of seeing a harm caused by DDIs and the extent to which the risk of DDIs affected the prescribers' drug selection. ANOVA with the post-hoc Scheffe test indicated that prescribers considered DDI information provided by "other" sources to be more useful than that provided by computerized alert system. CONCLUSIONS: This study suggests that prescribers' DDI knowledge may be inadequate. The study found that for the drug interactions evaluated, generalists performed better than specialists. In addition, this study presents an application of IRT analysis to knowledge and attitude measurement in health science research.