Evaluation of RxNorm for Representing Ambulatory Prescriptions

OBJECTIVE: We evaluated the RxNorm standardized drug nomenclature for representing ambulatory e-prescriptions. METHODS: Using a sample of 19743 primary care e-prescriptions, we estimated the coverage rate of RxNorm for representing clinical drugs, measured the 6-month replacement rate for RxNorm concepts, assessed the consistency of two independent concept mappings, and investigated inconsistent mappings. RESULTS: RxNorm contained concepts for nearly all prescriptions in the sample (99.995%). Of 1419 concepts used, 8.1% were replaced between April and October 2009. Independent mappings produced different concepts for 676 e-prescriptions (3.4%), but most differences would have low clinical significance. Most mismatches were related to the use of extended-release form concepts with no duration specified, inhalers vs. their contents, and clinically inert salts. CONCLUSIONS: RxNorm provides concepts covering nearly all ambulatory e-prescriptions in this setting. Independent mappings were relatively consistent. Improvements could be made by enabling selection of the most-specific concepts when broader prescribable concepts exist