Abstract
Background Adherence to prescribed medications is associated with improved health outcomes in many chronic conditions. Measures of adherence typically depend on administrative data from pharmacy dispensing databases and require a minimum of two drug dispensings to calculate (ongoing adherence). Patients who do not pick up the initial prescription (primary non-adherers) or who fill it only once (early non-adherers) are excluded from calculations based on pharmacy databases. Reasons for non-adherence in primary and early non-adherent patients could be different from those in patients with ongoing dispensings who discontinue or who are not fully adherent to their medications and could vary across diseases or drug classes.
Aim To characterize primary and early non-adherers among a population of patients with diabetes, hypertension, and/or hyperlipidemia enrolled in an integrated health system.
Methods We identified Kaiser Permanente Colorado (KPCO) members with a newly-initiated order for a medication of interest in 2007 and 2008. Orders were identified using electronic health record data; these orders were sent to the pharmacy information management system (PIMS). From PIMS we determined if/ when dispensing occurred. We classified patients into ongoing adherence and primary and early non-adherence groups. If patients had new orders for more than one drug of interest, we classified them as early or primary non-adherers only if they were not in the ongoing adherence group for any of the drugs. Patients were also classified according to drug group (antidiabetic, antihypertensive, antihyperlipidemic, or multi-drug).
Results Of 15,417 patients with a newly-initiated order for a drug of interest, 1147 (7.4%) were in the primary non-adherence group and 3355 (21.8%) were early non-adherers. Individuals initiated on more than one drug were most likely to be in the ongoing dispensing group. Almost 10% (754 of 7636) of individuals prescribed an anti-diabetic or antihyperlipidemic drug did not fill their first prescription, twice as many as among those prescribed an antihypertensive drug.
Conclusions Excluding the relatively large proportion of patients who do not receive ongoing dispensings of a newly-initiated drug yields an incomplete picture of medication adherence and thereby the potential factors contributing to non-adherence. For example, we found primary non-adherence differed across therapeutic classes.
