Influence Of Cost Sharing Differentials On Therapeutic Substitution And Medication Adherence: The Story Of Statins In 2006

Abstract

all branded and generic monotherapy formulations of lisinopril, hydrochlorothiazide, metformin, and levothyroxine. Claims were considered GDDP-filled if the following criteria were met: the only recorded price paid was patient out-of-pocket, and the quantity dispensed and out-of-pocket pricepaid matched published GDDP pharmacy lists, including Walmart, Walgreens, CVS, RiteAid, and Kroger. Results: In 2006, the percentage of GDDP-filled prescriptions was low: 8.1% (N= 4,472,797) of hydrochlorothiazide, 4.0% (N= 3,880,992) of levothyroxine, 0.01% (N= 4,008) of metformin, and 0.0% of lisinopril. This increased in 2008, to 2.4% (N= 1,676,928) for metformin, 8.0% (N= 7,107,840) for lisinopril, 16.8% (N= 9,024,532) for hydrochlorothiazide, and 18.9% (N= 13,035,972) for levothyroxine. In 2009, all medications had a GDDP-filled rate around 20% or greater. The highest percentages were seen in 2010: 22.5% (N= 12,033,009) of hydrochlorothiazide, 25.1% (N= 27,033,234) of levothyroxine, 25.5% (N= 17,593,051) of metformin, and 29.6% (N= 30,115,329) of lisinopril. By 2012 this decreased, and 19.6% (N= 9,715,614) of hydrochlorothiazide, 20.3% (N= 20,813,050) of lisinopril, 22.1% (N= 21,425,226) of levothyroxine, and 23.2% (N= 17,842,540) of metformin prescriptions were GDDPfilled. ConClusions: By 2012, approximately 1 in 5 prescriptions for lisinopril, hydrochlorothiazide, metformin, and levothyroxine were filled using a GDDP. As they are cash-only, these prescriptions may not be processed via a pharmacy benefit manager, and therefore may be missing from insurance claims data.