Predictors of Nonadherence to Topical Intraocular Pressure Reduction Medications Among Medicare Members: A Claims-Based Retrospective Cohort Study

Reported adherence rates with ocular hypotensive medications typically range from 51% to 56% over the first year of therapy. As intraocular pressure (IOP) reduction slows the progression of vision loss from glaucoma, early identification of nonadherent members is crucial to effective disease management. To (a) identify member characteristics and other factors related to nonadherence with topical IOP-lowering medications available in administrative claims data and (b) create a predictive model incorporating these variables. This retrospective cohort study analyzed data from Humana's administrative claims database. The study cohort included members aged 65-89 years enrolled in a Medicare Advantage Prescription Drug plan (MAPD; medical and pharmacy benefits), with > 1 topical IOP-lowering medication claims between January 2011 and September 2012 and a minimum of 24 months of continuous enrollment-12 months before and 12 months after the initial (index) prescription claim for a topical IOP-lowering medication. Adherence was defined as the proportion of days covered (PDC) with drug supply (calculated from the number of drops per bottle and dose) over the first year after the index prescription. Members with PDC > 0.80 were considered adherent, while members with PDC < 0.80 were considered nonadherent. Multivariable stepwise logistic regression with backward elimination was used to construct a predictive model for the likelihood of nonadherence (PDC < 0.80). The model was developed using 28 input variables*#x2013;10 variables were retained in the final model. 73,256 MAPD members were included in this study; most (69%) of these members were continuing topical IOP-lowering medication users. The proportion of patients adherent (PDC > 0.80) to IOP-lowering medications was 51%. The study sample was split, using a 2:1 ratio, into a development sample (n = 48,840 members) and a validation sample (n=24,416 members). The model performed equally well in the development sample and the validation sample (area under the curve = 0.71 for development and validation sets), making it appear robust in this Medicare population. In the final predictive model, characteristics increasing the likelihood (P < 0.01) of nonadherence to IOP-lowering medication within the MAPD population included index IOP prescription filled through mail order, higher medical costs during the pre-index period, being a new IOP-lowering medication user, and being male. Characteristics that lowered the likel