Impact of Medicaid preferred drug lists on therapeutic adherence.

OBJECTIVE To estimate rates of non-adherence for statins following implementation of a preferred drug list (PDL). STUDY DESIGN A retrospective cohort study. METHODS A difference-in-difference-in-difference approach was used to estimate the impact of a PDL on the use of statins in an Alabama Medicaid population. The PDL restricted access to certain branded medications and imposed a monthly prescription limit. The use of restricted drugs was compared with the use of unrestricted drugs in the months before and after the PDL in North Carolina (where there were no such restrictions) and Alabama. Pharmacy data from 2001 to 2005 were used to examine the effect of the Alabama PDL implemented in 2004. RESULTS Following the PDL in Alabama, Medicaid beneficiaries treated with statins had an 82% higher relative odds of becoming non-adherent with statin therapy compared with North Carolina and with pre-PDL Alabama [odds ratio (OR) 1.82, 95% CI 1.57, 2.11]. Furthermore, patients taking a restricted statin were more likely to be non-adherent than unrestricted patients (OR 1.42, 95% CI 1.12, 1.80). In addition, among Medicaid beneficiaries taking a restricted statin, people aged 65 years or older were more likely to be non-adherent than their younger counterparts after the PDL (OR 1.33, 95% CI 1.02, 1.73). Fifty-one per cent of patients in the Alabama sample were non-adherent with statin therapy after the PDL, compared with 39% before. Non-adherence was 36% in North Carolina in both periods. CONCLUSION The management of heart disease and high cholesterol are important challenges, especially for low-income patients. Policy makers should be aware that access restrictions can have adverse consequences for patient adherence.