Novel Adherence Measures for Infusible Therapeutic Agents Indicated for Rheumatoid Arthritis

Published studies on adherence to biologic medications show that many types of calculation methods are used. However, infused biologics are not well-suited to typical measures of adherence, such as proportion of days covered.

To construct and assess 7 novel adherence measures potentially applicable to infusible biologic agents and compare outcomes for 2 infusible biologics used for the treatment of patients with rheumatoid arthritis (RA).

Adults (aged ≥18 years) diagnosed with RA (ie, 2 or more 714.x claims) who received ≥24 months of continuous medical and pharmacy eligibility and who started taking abatacept or infliximab therapy were selected from a large commercial insurer database of medical and pharmacy claims. The 7 new adherence measures included cumulative amount of time with a refill gap ≥20% (CG20) beyond the expected infusion interval, cumulative time off treatment, days of uninterrupted use (DoUU), observed versus expected refill ratio (OvERR), repeated observations of underuse (RoUU), variance in time between infusions, and time to discontinuation (TTD). Mean observed infusion intervals were calculated and served as a reference measure of adherence.

The mean maintenance intervals approximated recommended guidelines. The mean observed infusion interval for abatacept recipients was 33 days (recommended, 28 days); it was 53 days (recommended, 56 days) for patients receiving infliximab. Three measures demonstrated a significant positive relationship to the mean observed infusion interval-CG20 (r = .258), DoUU (r = .212), and TTD (r = .081; P <.05). OvERR (r = -.072) and RoUU (r = -.189; P <.05) showed significant negative correlations. Real-world comparisons showed that adherence was significantly (P <.001) greater for the infliximab group according to most measures.

New measures of adherence correlate significantly with mean maintenance intervals. Future studies should examine relationships between these adherence measures and clinically relevant end points and/or cost outcomes to determine their predictive utility. Alternative methods of reporting adherence may have greater clinical significance than traditional measures.