You are correct. The VA NDF and Class still exist in the world, and can be downloaded. I don’t quite remember what happened, but in 2017 the NLM stopped distributing them with the RxNorm delivery, and declared that they are no longer maintained. Instead, MED-RT is the new classification system.
But the latter didn’t happen that way. NDF and VA Class are still going strong. At the time, we decided to focus on ATC as the main drug class, because of its much wider adoption internationally. The VA Classes only collect US drugs. Phenotype definitions based on it notoriously won’t work outside the country. We therefore decided not to bring it back, but happy to change our minds if there is a good use case. Is there? Do you guys need it for OHDSI-type research? We could re-integrate them into RxNorm, this time through the UMLS.
We never adopted MED-RT. Problem is a structure that doesn’t dwell well in our hierarchical world. For example, the class of vitamin agonists are descendents of the actual vitamin. We don’t work that way. Ingredients (whether the orginal or an agonist) have the same level below a class. We were thinking to do some surgery on MED-RT and revert those oddities, but then decided it would be too much work for a questionable purpose, and threw all efforts on ATC.