Methods to Assess Medication Adherence
The descriptions of data collection methods are presented in Table 4. Out of 33 studies used data collection methods to measure medication adherence, 22 (66.6%) studies used a self-report data collection method, pharmacy refill and claims database 9 (27.3%), and pill count 2 (6.1%). Moreover, the selected studies used various data sources; the majority obtained from patients (n=21), and direct methods were not used in the included studies. As previously mentioned the variation of the prevalence of medication adherence, the rate of adherence as assessed by using self-reported, claims database/refill data, pill count, health provider’s report (self-report, patient record) ranged from 10.6% to 81%, 19,21-23,34,46-62 10% to 62.9%,25,34,63-70 45%,71,72 and 69.2% to 85.4%,34,58 respectively. The most common included studies utilized standardized and structured data collection tool, and structured interviews to measure adherence. Morisky Medication Adherence Scale-8 items (MMAS) and the four-item Morisky Green Levine Medication Adherence Scale (MGLS) self-report measure was the most common measures used for evaluating medication adherence, which was applied in 5 (23.8%),22,23,46,47,51 and 4 (19%) studies,52,53,55,56 respectively.
Nine studies used the electronic data records (pharmacy or medical claims database) to measure medication adherence, which different measures were utilized, including the percentage of days covered (PDC), medicine possession ratio (MPR), prescription fill, and missing days. The PDC is the number of days a patient gets each medication divided by the number of days for eligibility for medication, greater than 80% mean patient have adequate adherence, which 80 % considered cut-off between adherent and nonadherent patients as used by LeBlanc et al.68 Also, the MPR is the number of days that doses were dispersed divided by the total number of days between the first and last doses. It is dichotomized into greater than 80% considered adherent and lower than or equal 80% considered nonadherent as used by Holvast et al66, and Slabbert et al69 reported that patients considered adherence if MPR was between ≥80% and ≤110%.
Regarding prescription fill and missing days, nonadherence described if medication discontinued before 180 days after the index refill date.63 Other studies defined adherence as the proportion of compliance during the first 24 weeks from prescription fill.67 Also, Yau et al25 measured adherence as filled prescriptions for medications with no gaps of more than 15 days within six months after the start of treatment. On the other hand, two studies used pill count by calculating the actual number of pills taken dividing by the expected number of pills taken during the study period and multiplying by 100.71 Other study was calculated by the total number of weeks the participants took medication.72