Merging Veterans Affairs rheumatoid arthritis registry and pharmacy data to assess methotrexate adherence and disease activity in clinical practice

Objective The Veterans Affairs (VA) Rheumatoid Arthritis (VARA) registry and the VA Pharmacy Benefits Management database were linked to determine the association of methotrexate (MTX) adherence with rheumatoid arthritis (RA) disease activity. Methods For each patient, the medication possession ratio (MPR) was calculated for the first episode of MTX exposure of a duration of ≥12 weeks for both new and established MTX users. High MTX adherence was defined as an MPR ≥0.80 and low MTX adherence was defined as an MPR