Poor adherence to medication therapy is a longstanding challenge in the healthcare community and is now recognized as a public health crisis.1 The World Health Organization reports adherence at approximately 50 percent among patients taking medications for chronic illnesses.2 Poor adherence has been associated with reduced quality of life, disease progression, mortality, and increased healthcare costs in the United States.3 Hospitalization due to poor medication adherence is linked to approximately 125,000 deaths per year and an estimated healthcare cost of $100 billion annually.3
Two related terms, compliance and adherence, are commonly used to describe patient medication-taking behavior.4 Compliance is the extent to which patient behavior matches the prescriber's care plan as determined by the provider alone and implies patient disobedience when not followed. Clinical practice has shifted away from the term "compliance," with clinicians now favoring "adherence" as an alternative. Adherence is the extent to which patient behavior aligns with clinical decisions that were mutually decided upon by the patient and provider. In contrast to compliance, adherence encompasses patient freedom of choice and does not blame the patient for non-adherence. The movement to using adherence in place of compliance represents an important shift toward empowering the patient in health-related decisions in today's practice of patient-centered care.
Patient non-adherence may result in incorrect administration technique, self-dosage adjustment, delayed timing of dosing, dose omission, and inappropriate discontinuation of medications. Non-adherence can occur unintentionally due to forgetfulness or cognitive impairment, health illiteracy (e.g., lack of understanding of the disease or proper use of the medication), or difficulties accessing medication (e.g., affordability or transportation barriers).5 On the other hand, a patient can be intentionally non-adherent because he or she is swayed by beliefs or fears that justify not taking the medication as prescribed.5
Poor patient-provider communication has been identified as a main source of medication non-adherence. In a study of patients with chronic kidney disease, researchers found that patients omitted medications that they considered "less important" and a substantial divide existed between patients' beliefs about medications and generally accepted medical opinion.6 Therefore, adequate patient education regarding the purpose of the medication and their expectations of therapy is imperative to motivating patients to take medications appropriately. Lack of provider empathy or frequent use of medical terminology may inhibit a patient from developing trust and may cause apprehension in seeking resolution to medication-related questions and concerns. Significant influences on non-adherence that are related to the health system include high co-pays or cost of medication, insurance formulary restrictions, and a structure of preferred and non-preferred pharmacies that may restrict prescription access. These healthcare system barriers may prevent prescription fulfillment, often without involving the provider to prescribe an alternative.
The two main classifications for measuring adherence are direct and indirect. Direct methods include direct observed therapy (DOT)—monitoring of drug and/or metabolite levels in blood or urine samples and use of ingestible event markers. These strategies can be performed accurately but hold significant limitations in practice. Measurement of drug concentrations in biologic samples and utilization of drug formulations with adherence trackers are often impractical and too expensive for widespread use. DOT is susceptible to patients feigning medication ingestion and is a cumbersome process to implement for the healthcare team.5,7,8
Indirect methods of adherence are preferred over direct methods because they are convenient, noninvasive, and allow for analysis of patient and population-based adherence patterns. Examples include the use of prescription fill and claims databases, pill counts, patient self-reporting, patient medication logs, and clinical response or physiologic markers.5,8 Proportion of days covered and medication possession ratio are adherence measures based on prescription fill records that are often utilized by payors and researchers for retrospective adherence monitoring.9 A disadvantage is that medications may be picked up routinely but not taken as prescribed after leaving the pharmacy. It is also possible for the adherence of patients with certain disease states to be skewed due to frequent need for dosage adjustments and medication changes common to clinical management. For example, patients on hemodialysis may be instructed to hold antihypertensive medications prior to or following dialysis to avoid hypotension, which would cause patients to appear non-adherent due to later than expected refills. Monitoring improvement in clinical status or physiologic markers is sometimes useful, although confounding factors exist such as non-pharmacologic intervention and self-limiting signs/symptoms that may elicit clinical response independent of medication use.5,8 Additional methods used to assess adherence include targeted patient interviewing, review of patient diaries, and examination of pill bottles. However, these have poor reliability due to potential misrepresentation by patients often leading to overestimation of adherence.
Multiple strategies to improve medication adherence using integrated pharmacy models and community pharmacy interventions have been explored. Although multiple concepts and definitions have been described, integrated pharmacy models typically involve a working relationship between pharmacy professionals and multiple healthcare disciplines. Integrated pharmacy models have demonstrated benefits to patients with chronic illness in clinical trials. Authors from a study of 30,574 hemodialysis patients evaluated differences in mineral and bone disorder laboratory markers in individuals receiving coordinated medication delivery and adherence support from a renal pharmacy. The results demonstrated that renal pharmacy patients were more likely to achieve target serum calcium, phosphorus, and parathyroid hormone compared to those who did not receive integrated pharmacy services.10 In a retrospective cohort analysis, patients using pharmacies integrated within community mental health centers had higher medication adherence rates, lower rates of hospitalization, decreased emergency department use, and reduced cost of care compared to those filling their prescriptions at community pharmacies.11
Community pharmacy models aimed at improving medication adherence most often involve pharmacists who provide disease-related interventions, patient education, and follow-up. In a recent systematic review, community pharmacist-led interventions showed improvement in medication adherence and disease-state control in patients with hypertension, dyslipidemia, chronic obstructive pulmonary disease, and asthma.12 Additional services intended to improve medication adherence include pickup and refill reminders, automatic prescription refills, medication synchronization, and blister packaging.13,14
Medication adherence is a complex public health issue that demands continued progress to overcome a multitude of patient, provider, and health system barriers. Pharmacists can take a lead role in delivering effective patient care services to improve medication adherence and optimize patient outcomes.