Use of pharmacy dispensing data to measure adherence and identify nonadherence with oral hypoglycemic agents

A framework for calculation of adherence for oral hypoglycemic agents (OHAs) based on data from health-insurance claims is available. Pharmacy dispensing data aid identification of nonadherent patients in pharmacy practices. However, use of these data for calculation of OHA adherence requires additional methodological categories. We examined the impact of different methodological choices on estimation of OHA adherence using pharmacy dispensing data.

Four methodological categories were added to the framework available to be used for adherence calculation with pharmacy dispensing data. Three adherence measures were defined to supply pharmacists with significant information on OHA use of their patients: (i) percentage of days covered by use periods of dispensed medication (PDC), (ii) mean rate of adherent patients with a PDC ≥80 % (MRAP80), and (iii) mean number of nonadherent patients (MNNP80) per pharmacy with a PDC <80 %. A basic scenario was developed from 16 methodological categories. Consequences of choices for different parameters within these categories on the scores of the three adherence measures were calculated from dispensing data between July 2013 and July 2014.

Data were available for 604,500 OHA users in 1737 community pharmacies in the Netherlands. For the basic scenario, mean PDC for OHA was 88.3 %. MRAP80 was 80.3 %, which corresponded to an average of 69 nonadherent patients per pharmacy. Different choices for parameter values resulted in score variations for PDC of 85.0-91.8 %, for MRAP80 of 75.3-86.1 %, and between 49 and 92 MNNP80 per pharmacy.

Sixteen methodological categories specified calculation of OHA adherence based on pharmacy dispensing data. Adherence scores expressed as percentages were relatively robust to variation in parameter values, but differed substantially for the absolute numbers of nonadherent patients per pharmacy.