Adherence vs. persistence

MTM Pearls

For the past year, Towncrest Pharmacy has been working with a payer on a pilot project to assess how community pharmacists can affect their patients’ clinical outcomes in terms of medication adherence and persistence. Before this project began, we had already been monitoring our patients’ adherence to statins, renin angiotensin system antagonists, and oral diabetes medications based on CMS performance measures for pharmacists. Although we felt we had a good understanding of adherence and how it is calculated based on proportion of days covered (PDC), we were not as sure about persistence. To help us get a better handle on persistence, I did a literature review and came across a small study that provided further information.

Key points

The work group performing the work, the International Society for Pharmacoeconomics and Outcomes Research, developed the following definitions of adherence (compliance) and persistence:

  • Medication adherence (compliance): “the extent to which a patient acts in accordance with the prescribed interval and dose of a dosing regimen.”

  • Medication persistence: “the duration of time from initiation to discontinuation of therapy.”

Compliance is measured over a period of time and reported as a percentage, whereas persistence is reported as a continuous variable in terms of number of days for which the therapy was available. Clinical outcomes are affected not only by how well patients take their medications but also by how long they take them.

MTM pearls

The problem I see with the current way adherence is being reported (i.e., PDC) is that this information is based on claims data. So, if patients receive refills for medications via automatic refills or another automated system, claims data may show appropriate adherence, but they don’t tell us how the patient is actually taking the medication or if they are even taking it at all. 

Patients may choose to stop a medication (i.e., nonpersist) for a variety of reasons: to avoid potential or actual adverse drug reactions; because they do not believe they need the medication or do not believe the medication is working; or even because a prescriber directed a medication change in some way (e.g., drug holiday, dosing change, drug discontinuation, samples given, etc.) 

Therefore, pharmacists need to talk to patients at each and every refill visit to find out how they are actually taking their medications. Unfortunately, at this time, payers are focused on the adherence (compliance) component based on claims data, but this component tells only a partial story. Only by talking to patients can pharmacists complete the story and really understand their patient’s medication-taking behaviors. 

In our own practice, we have found patients who stopped a medication that should not have been stopped because they were given improper advice from a friend or relative. We have also uncovered adherence and persistence issues when prescribers have changed the dose (e.g., a patient was told to halve the dose). To address this problem, we implemented a simple intervention: requesting a new prescription with the correct directions. 

In a previous column, I described the processes we use to ensure that we provide prospective medication reviews for all patients coming into the pharmacy. We have described this process as continuous medication monitoring (CMM). In addition, we have coined and trademarked the phrase “Make Every Encounter Count” to emphasize the importance to our staff pharmacists of optimizing each patient encounter to ensure that our patients are receiving safe and effective medications. 

The Thriving Pharmacist

Recently my business partner and I started a blog called The Thriving Pharmacist ( to provide helpful tips to busy community pharmacists on implementing CMM processes. Since adherence and persistence are important clinical parameters from a payer perspective, community pharmacists need to make sure they have the proper knowledge and tools to have an impact on these measures.


  1. ISPOR. 2008;11(1):44–47