Background/Purpose: Adherence is under consideration for quality reporting in a number of disease states. Published data on adherence of biologics reveal a wide range of calculation methods. Biologics administered via infusion do not lend themselves to the typical measures of adherence, such as the medication possession ratio (MPR) or proportion of days covered (PDC). The purpose of this study was to investigate a number of newly constructed proxies for medication adherence across two of the more commonly prescribed infusible biologic agents: infliximab (IFX) and abatacept (ABA).

Methods: Using the Optum^TM Clinformatics^TM database of insured individuals, IFX (n = 417) and ABA (n = 431) members who were continuously eligible for benefits one-year post-induction were selected for adherence analyses.  New measures of medication adherence were designed for calculation over the maintenance phase of treatment (Table 1). For both IFX and ABA, the fourth dose constitutes the beginning of maintenance. Maintenance infusions are recommended every eight weeks for IFX and every four weeks for ABA. The total study measurement period was one year, beginning with the induction infusion, though only maintenance infusions were subjected to adherence measures. As a reference, mean maintenance intervals were also calculated for both groups.

Results: Mean maintenance intervals approximated recommended guidelines. IFX patients had a mean observed infusion interval (MOII) of 53 days (recommended 56 days) while ABA patients demonstrated a MOII of 33 days (recommended 28 days). ABA patients had a significantly greater amount of CToTx than IFX patients (78.56 vs 61.08 days), and a significantly shorter number of DoUU (164 vs 286 days). ABA patients had a significantly lower OvERR than IFX patients (0.73 vs 0.97), and were over 3 times as likely as IFX patients to show a PtRG ≥ 20% (68.4% vs 20.63). The ROoUU was more than 4 times higher for ABA than IFX patients (1.91 vs 0.42), while the CATRG≥20% was also higher for ABA patients (32.23 days) compared to IFX patients (20.63 days).  Finally, the ViTBR for 0-7 days was lower for ABA patients than IFX patients (88.2% vs 93.2%). All measured adherence outcomes were significantly different between groups (p < 0.001).

Conclusion: This study piloted a number of measures designed to assess infusion adherence.  Results indicated more favorable adherence outcomes for IFX-treated patients compared to ABA patients. Substantial differences may result from assumptions made regarding days’ supply and calculation methods for adherence when using medical claims. Quality reporting should include all details for days’ supply assumptions and calculation methods. Future studies should examine the relationship between these new measures of adherence and more clinically relevant endpoints and/or cost outcomes to determine if they possess any predictive utility.