Development of an Algorithm to Detect Methotrexate Wrong Frequency Error Using Computerized Health Care Data

The authors validated an algorithm to detect frequency errors in computerized healthcare data and estimated the incidence of these errors in an integrated healthcare system. Authors identified potential methotrexate frequency errors using ICD‐9 code 995.20 (adverse drug event), Current Procedural Terminology (CPT) code 96409 for injection of leucovorin and prescription refill patterns and performed chart review to confirm the frequency errors, assessed performance for detecting frequency errors, and estimated the incidence of chart‐confirmed errors. This method is generalizable to other medications with serious adverse events treated with antidotes.