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Map From CPIC Level A Medication Ingredient Codes to RxNorm Codes Commonly Found in an EHR

A growing number of folks interested in pharmacogenomics (PGx) rely on the recommendations coming from CPIC and PharmGKB.

CPIC is an international consortium focused on facilitating the use of PGx tests for patient care. CPIC started as a shared project between PharmGKB and the Pharmacogenomics Research Network (PGRN) in 2009. CPIC guidelines are indexed in PubMed as clinical guidelines, endorsed by ASHP and ASCPT, and referenced in ClinGen and PharmGKB.

PharmGKB is a comprehensive resource that curates knowledge about the impact of genetic variation on drug response for clinicians and researchers. PharmGKB provides annotations of clinical guidelines written by CPIC. What’s more, PharmGKB indexes the medications involved in drug-gene interactions with RxNorm codes (available on the PharmGKB downloads page). This is convenient because RxNorm codes are heavily used — in fact, their use is mandated — for various medication-related contexts in EHRs.

PGx Clinical Decision Support

But there is still a bit of a disconnect when, for instance, you want to look at the RxNorm code of an ordered medication and see if it has a known drug-gene interaction. The NLM creates RxNorm codes for different levels of medication abstraction — for instance, RxNorm ingredient codes, codes for brand name drugs, codes for generic drugs, etc. The RxNorm codes assigned by PharmGKB are ingredient-level codes, whereas the RxNorm codes used in EHRs are generic and branded drug codes.

Let’s take ‘abacavir’ as an example. PharmGKB associates abacavir with the RxNorm ingredient code ‘190521’ (abacavir), whereas in an EHR order entry system, we might find ‘242679’ (abacavir 300 MG Oral Tablet), ‘213460’ (abacavir 300 MG Oral Tablet [Ziagen]), etc.

The good news is that the RxNorm database provides a rich set of relationships that enable one to compute the set of RxNorm codes likely to be found in an EHR given the ingredient code.

Here at Elimu, where we’ve been developing PGx Clinical Decision Support, we put together a table of value sets that map from CPIC Level A medication ingredient codes to the RxNorm codes you’d expect to find in an EHR. Please reach out if you’d like a copy — we hope you find it helpful!