Abstract
Background/Aims In 2006, pharmacy retailers began offering low cost generic medications at costs ranging from $4 for a 30-day supply to $10 for a 90-day supply. One is now offering free generic metformin. There are considerable cost savings for patients who take advantage of these programs. However, filling medications at multiple pharmacies could lead to incomplete medication histories within pharmacy and insurance records thus making it difficult identify drug interactions and to address quality initiatives. This study will measure trends in requests for prescriptions to be filled within an integrated health system pharmacy versus an outside pharmacy retailer before and after the availability of free metformin in March 2010. Characteristics of patients who switched from prescriptions for internal fills to external fills after free metformin was available will also be examined.
Methods Electronic medication prescription order data from January 2009 to December 2011 will be used in the study. Patients with diabetes will be identified by two outpatient visits, one emergency department visit, or one hospitalization with a diagnosis code for diabetes and use of an oral antidiabetes medication. Monthly metformin prescription rates will be compared to generic sulfonylurea prescription rates; sulfonylureas are not available for free. Patients will be included in the analysis if they have 12 months of continuous enrollment with no evidence of either a fill or a prescription order for metformin or a sulfonylurea during that time. An interrupted time series analysis with segmented regression will be used to study the impact of free generic metformin on requests for outside prescription fills. A logistic regression difference-in deference model will be used to study the impact of the availability of free metformin on pharmacy switching. We will also examine the relevance of the following characteristics on switching, demographics, health plan product, number of medications, the day supply usually filled, percent of medications that are generic, copay, and distance to medical office building from residence.
Results Analysis is ongoing.
Discussion This study will help measure the extent of external medication fills and characteristics of patients who fill medications externally in a market where medications are available for free.
