Pharmacy's Multisite Study of Health Systems Evaluates Adherence to Disease-Modifying Self-administered Antirheumatic Drugs

Pharmacy’s Multisite Study of Health Systems Evaluates Adherence to Disease-Modifying Self-administered Antirheumatic Drugs

High treatment adherence is a critical first step towards better patient outcomes, including prolonged disease control or remission.

Adherence to self-administered biological disease-modifying antirheumatic drugs (bDMARDs) is a key component in enabling patients to obtain therapeutic benefit from these expensive therapies. Healthcare specialist pharmacies (HSSPs) have reported high adherence rates in various disease states; however, there is limited literature describing adherence rates in rheumatoid arthritis (RA) patients 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 all healthcare systems.

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

All HSSPs had access to their healthcare system electronic health records (EHRs), which allowed for a complete clinical patient review for the purpose of this study, as well as facilitating clear communication with prescribers. To be included in the study, patients needed to have 3 or more dispensations of bDMARD between January 2018 and December 2018, bDMARD prescriptions written by a prescriber within the participating site, and have international disease classification documentation code M05, M06, or M08.

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

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

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

An adjusted PDC was calculated for these patients when the review identified clinically appropriate gaps, such as documented changes in the prescriber’s dosing instructions, use of specimens, maintenance of pregnancy treatment, or identification of missing fillings. This adjusted PDC was calculated by removing the appropriate interval days from the PDC denominator.

There were 29,994 prescriptions from 3,530 patients included in 20 HSSPs. The original median PDC (ie, pre-revision PDC of patients with a PDC <0.8) was 0.94 (IQR, 0.83-0.99).

A total of 420 patients with an initial PDC <0,8 ha richiesto un aggiustamento della propria PDC dopo la revisione della cartella a causa dell'identificazione di lacune terapeutiche clinicamente appropriate. La PDC mediana finale era 0,95 (IQR, 0,87-0,99), con l'87,9% dei pazienti con una PDC >0.8.

The main median PDC result across all sites is 0.95 (95%) demonstrating that patients receiving prescriptions and supplemental pharmacy services from HSSP maintain a high level of drug adherence. The DMARD adherence rates observed in this study are much higher than in previous reports, ranging from 44% to 83%. Only 12% of HSSP patients in this study had a PDC <80%, which is the level recommended by the PQA.

High treatment adherence is a critical first step towards better patient outcomes, including prolonged disease control or remission. This study is among the first to evaluate the frequency of appropriate gaps in therapy and how they affect overall adherence rates: in the specialty, more is not always better.

Patients are often told to discontinue treatment due to clinical factors or events, and this is not taken into account in the 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 filling history.

The pharmacy complaint data alone does not tell the whole story of joining. The use of adherence measures such as PDCs to evaluate pharmacy performance by payers, accrediters and other stakeholders is on the rise. However, the use of PDC can 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 multisite searches. HSSPs make up a small but important and growing percentage of the specialty pharmaceutical sector. This study marks an important step in the journey towards continued collaboration, the development of best practices and the improvement of patient care.

The Health-System Specialty Pharmacy Outcomes Research Consortium plans to continue producing multisite research studies that demonstrate the value of our model. We believe that the recent ASHP definition of HSSP is true: “an integrated model of advanced practice that incorporates the management of the use of specialty drugs across the continuum of care” and that this model of care produces superior outcomes and experience for patients compared to not HSSP.

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 pharmacies and network among members. If you or your site are interested in joining the consortium, please email

* In 2017, the Vanderbilt Specialty Pharmacy Health Research and Outcomes team created a collaborative consortium with the goal of promoting cross-site research opportunities, educational activities and networking among specialized health care pharmacies across the country. As of spring 2022, the consortium consists of 46 HSSPs.


Zuckerman AD, DeClercq J, Choi L, et al. Adherence to biological disease-modifying antirheumatic drugs self-administered in specialized pharmacies of the healthcare system. Am J Health Syst Pharm. 2021; 78 (23): 2142-2150. doi: 10.1093 / ajhp / zxab342.

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