In patients with type 2 diabetes, initial use of an extended-release formulation of metformin may be cost-saving, according to study results published in Diabetes Care. Although the cost is higher, adherence to extended-release metformin treatment was found to be better.
Previous studies have reported that approximately two-thirds of metformin-treated patients adhere to their prescribed regimen. This high rate of nonadherence is mostly due to cost issues and side effects of the treatment. Metformin extended-release formulations may reduce side effects compared with immediate-release formulations.
The goal of the current retrospective cohort study was to assess the influence of cost and initial choice of formulation (extended- or immediate-release) on adherence and persistence to metformin.
Data from commercial insurance carriers in the United States from January 2012 to December 2016 were used. The cohort included 81,406 adults (46% women) with type 2 diabetes who filled an initial prescription for metformin.
Persistence, defined as ≥1 metformin prescription claim during the 6- to 12-month window after the initial prescription, was the primary outcome. Adherence, defined as the percentage of days for which the patient had filled sufficient prescriptions, was the secondary outcome.
Of the total initial prescriptions for metformin, 26% were for extended-release metformin, which had a higher median total ($6 vs $5) and out-of-pocket cost ($5 vs $4) compared with immediate-release formulation (P <.01 for all differences).
Persistence rates were higher with extended-release metformin compared with immediate-release formulation (75% vs 73%). Adherence rates (62% vs 59%, respectively) and adequate adherence, defined as adherence ≥80% during the first year of follow-up (42% vs 37%), were also higher with extended-release metformin compared with immediate-release metformin.
After adjustment for cost, dose, demographics, and comorbidities, the adjusted odds ratio for persistence was higher for extended-release metformin compared with the immediate-release formulation (odds ratio, 1.14; 95% CI, 1.10-1.18; P <.001). The adjusted relationship between persistence and cost was nonlinear, with the highest persistence in the lowest-cost quartile and a lower relative persistence in all of the higher-cost quartiles.
Overall, although the cost of extended-release metformin was slightly higher, initial use of this formulation was associated with better adherence.
“We believe these findings provide the strongest evidence to date that routine initial use of [extended-release] metformin is a simple intervention that may improve adherence,” concluded the researchers.
Flory JH, Mushlin AI. Effect of cost and formulation on persistence and adherence to initial metformin therapy for type 2 diabetes [published online April 6, 2020]. Diabetes Care. doi:10.2337/dc19-2426