Abstracts

Rationale: Adherence to the prescribed drug regimen is a major step in achieving the goal of reduced seizure burden in patients with epilepsy. Decreased antiepileptic drug (AED) adherence is associated with more than a 3-fold increase in mortality and significantly more emergency department visits, hospital admissions, injuries and fractures (Faught 2008). An objective measure of adherence is the Medication Possession Ratio (MPR). This is a numeric value typically between 0 and 1 with a value closer to 1 indicating greater adherence. It is calculated from pharmacy refill records over a set time period. A widely accepted value for being classified as adherent is an MPR > 0.8. Preliminary MPR data from one of our ongoing investigator-initiated projects had raised some concerns about our outpatient clinic population. The objective adherence data (MPR) was not matching what patients stated when asked about their adherence (subjective adherence). This preliminary data caused us to look at a larger patient sample to determine if a gap existed in subjective and objective measures of AED adherence. Methods: Both subjective and objective adherence data were compared in patients with epilepsy for this cross-sectional study. During their clinic interview, patients were asked to self-assess their AED adherence (subjective measure of adherence). The objective measure of adherence was an MPR for each of their AEDs. We contacted each patient's community pharmacy and used refill records to calculate their MPR for the 6 months prior to their clinic visit. Patients provided consent for us to contact their pharmacy. Results: Data from 27 patients (17 female) with an average age of 35.22 (± 11.21) years was examined. Eighteen patients reported a seizure within the last 30 days. All patients described themselves as "adherent" when asked at their clinic visit (subjective adherence). This is contrast to the MPR data (objective adherence). Of 45 AEDs taken in the 27 patients (14 patients on AED monotherapy), the MPR was <0.8 for 16 of the AEDs. Ten of the 27 patients (37%) had an MPR <0.8 for at least one of their AEDs. Interestingly, AED burden did not appear to impact the MPR as 6 of the 10 patients with MPRs <0.8 were on AED monotherapy. Conclusions: The reason for the gap in the subjective and objective measures of adherence is unclear. One explanation could be that patients are not completely truthful in their subjective assessment of their adherence. Other factors could be associated with limitations in calculating their MPR; a single number to represent AED adherence. Limitations of the MPR include, but are not limited to 1) a lack of sensitivity to changes in doses like tapering an AED up or down and 2) patients could use more than one pharmacy. In conclusion, we identified a gap in the subjective and objective measures of AED adherence with more than one-third of the patients deemed to be non-adherent from objective data (MPR <0.8). The reasons for this gap are likely multifactorial.