Multisite Health-Systems Specialty Pharmacy Study Evaluates Adherence to Self-Administered Biologic Disease-Modifying Antirheumatic Drugs


High adherence to treatment is a key first step toward better patient outcomes, including sustained disease control or remission.

Adherence to self-administered biologic disease-modifying antirheumatic drugs (bDMARDs) is a key component to patients achieving a therapeutic benefit from these expensive therapies. Health-system specialty pharmacies (HSSPs) have reported high adherence rates across several disease states; however, there has been limited literature describing adherence rates in patients with rheumatoid arthritis (RA) using an HSSP.

Recently, 20 health-systems within the Vanderbilt Health-System Specialty Pharmacy Outcomes Research Consortium* collaborated to perform the first multisite study evaluating adherence and reasons for poor adherence to DMARDs across health-systems.

In the multisite, retrospective cohort study, each participating site had an HSSP integrated with health-system specialty clinics, either in a centralized, decentralized, or mixed practice model. Although each health-system differed slightly in their specific support model, all provided dedicated specialty pharmacy services to patients with RA.

All HSSPs had access to their respective health-system electronic health records (EHRs), which allowed for comprehensive patient clinical review for purposes of this study, as well as facilitated clear communication with prescribers. To be included in the study, patients were required to have 3 or more dispenses of bDMARDs between January 2018 and December 2018, bDMARD prescriptions written by a prescriber internal to the participating site, and have documentation of International Classification of Diseases code M05, M06, or M08.

The study used proportion of days covered (PDC) to calculate medication adherence. PDC uses pharmacy claims to calculate the time a patient has medication in hand and is the industry standard, endorsed by the National Association of Specialty Pharmacy, the American Society of Health-System Pharmacists (ASHP), and the Pharmacy Quality Alliance (PQA). The PQA recommends patients on bDMARD therapy achieve a PDC of >0.8 (80%).

Initial PDC was calculated by generating a supply diary for each patient from the time of index prescription to the date of the last fill, omitting the days’ supply in the patient’s last fill. A single PDC value was calculated for each patient, with all fills for any included medication for a single patient analyzed in aggregate.

Once the initial PDC was calculated, sites were given a list of study IDs and gap dates for patients with a PDC of <0.8. Each site then reviewed their EHR and pharmacy dispensing records for patients with a PDC of <0.8 to assess the reason for gaps in the fill data.

An adjusted PDC was calculated for these patients when the review identified gaps that were clinically appropriate, such as documented changes in dosing instruction from the prescriber, utilization of samples, holding treatment for pregnancy, or the identification of missing fills. This adjusted PDC was calculated by removing appropriate gap days from the PDC denominator.

There were 29,994 prescriptions from 3530 patients included across 20 HSSPs. The original median PDC (i.e., the PDC prior to review of patients with a PDC of <0.8) was 0.94 (IQR, 0.83-0.99).

A total of 420 patients with an initial PDC of <0.8 required adjustment of their PDC after chart review due to identification of clinically appropriate treatment gaps. The final median PDC was 0.95 (IQR, 0.87-0.99), with 87.9% of patients having a PDC of >0.8.

The primary finding of the median PDC across all sites being 0.95 (95%) demonstrates that patients receiving prescriptions and integration pharmacy services from HSSPs maintain a high level of medication adherence. The adherence rates to DMARDs observed in this study are much higher than previous reports, which range from 44%-83%. Only 12% of patients at HSSPs in this study had a PDC <80%, which is the recommended level by PQA.

High adherence to treatment is a key first step toward better patient outcomes, including sustained disease control or remission. This study is among the first to assess the frequency of appropriate gaps in therapy and how they impact overall adherence rates—in specialty, more is not always better.

Patients are often told to hold treatment due to clinical factors or events, and this is not accounted for in traditional use of adherence measures, such as PDC. We found that most patients with low PDC had an appropriate reason for having gaps in their refill history.

Pharmacy claims data alone do not tell the whole story of adherence. The use of adherence measures such as PDC to assess pharmacy performance by payers, accreditors, and other stakeholders is increasing. However, reliance on PDC may provide an inaccurate picture of patient care or quality unless these data are confirmed or supplemented by additional clinical information, such as the review performed in this study.

This study also demonstrates how HSSPs can leverage their ability to aggregate data and perform multi-site research. HSSPs make up a small but important and growing percentage of the specialty pharmacy industry. This study marks an important step on the journey to continued collaboration, development of best practices, and improvements to patient care.

The Health-System Specialty Pharmacy Outcomes Research Consortium plans to continue to produce multisite research studies that demonstrate the value of our model. We believe the recent ASHP definition of an HSSP holds true: “an integrated advanced practice model that incorporates specialty medication-use management across the continuum of care,” and that this model of care produces superior patient outcomes and experience than non-HSSPs.

Any HSSP is welcome to join and contribute to the consortium. We also host monthly informal meetings to discuss recent articles and hot topics in specialty pharmacy and network amongst members. If you or your site are interested in joining the consortium, please email

*In 2017, the health outcomes and research team at Vanderbilt Specialty Pharmacy created a collaborative consortium with the goal of fostering cross-site research opportunities, educational activities and networking among health-system specialty pharmacies across the country. As of spring 2022, the consortium is composed of 46 HSSPs.


Zuckerman AD, DeClercq J, Choi L, et al. Adherence to self-administered biologic disease-modifying antirheumatic drugs across health-system specialty pharmacies. Am J Health Syst Pharm. 2021;78(23):2142-2150. doi:10.1093/ajhp/zxab342.

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