Retrieving the ingredients in RxNorm concepts

We would like to convert from RxNorm medications to their ingredients. RxNorm is an ontology, with terms connected by relationship types, which can be traversed to map ingredients. This is necessary to map RxNorm medications to DrugBank, enabling network inclusion. Additionally, we need to know when medications map to multiple ingredients as we are excluding combination therapies for the time being. Once the mapping is complete, we can proceed with integrating the ehrlink resource. This discussion will follow our attempts to map concepts to ingredients.

RxNorm term types

RxNorm concepts each have a specified term type (TTY). RxNorm documentation is oftentimes difficult to navigate, so we provide definitions for all term types below. The descriptions are from [1], while definitions were found here.

RxNorm API method

We found a method to retrieve ingredients using the allrelated RxNorm API command. An example query for rxcui 198440 looks like:

http://rxnav.nlm.nih.gov/REST/rxcui/198440/allrelated

Ingredients can be extracted from the returned xml with the following XPath query:

./allRelatedGroup/conceptGroup[tty='IN']/conceptProperties

We wrote a python script to perform this operation on the ehrlink [1] RxNorm medications mapped by @alizee. The resulting ingredient map is available for download.

To go further on resolving ambiguities when retrieving concepts, I had to look up abbreviations of the TTY too. I had seen the very useful link you mention above from the RxNav documentation, but I finally used the more general ressource that is the MetaThesaurus of UMLS. This page lists all the abbreviations used in the Rx system.

I extracted from this page the table with all the TTY abbreviations into a reusable csv file. It could be useful down the road to other people.