Adherence to a fixed-dose combination of rosiglitazone maleate/metformin hydrochloride in subjects with type 2 diabetes mellitus: a retrospective database analysis.

BACKGROUND: In 2002, fixed-dose combination therapy (FDCT) with rosiglitazone maleate plus metformin hydrochloride became available for the treatment of type 2 diabetes mellitus (DM-2) in subjects whose disease was uncontrolled on monotherapy with metformin or a thiazolidinedione. FDCT allows a reduced pill burden and a less complex medication regimen.

OBJECTIVE: The objective of this study was to assess changes in medication adherence rates associated with oral hypoglycemic agents in subjects switching from either monotherapy or dual therapy with metformin and/or rosiglitazone to rosiglitazone-metformin FDCT.

METHODS: In this retrospective database analysis, data were obtained from the pharmacy claims database of a large health benefits company. Prescription claims for subjects aged > or =18 years with DM-2 whose disease was uncontrolled on monotherapy with metformin or a thiazolidinedione were analyzed over a 12-month study period (a 6-month preindex period and a 6-month postindex period). Some subjects were receiving monotherapy with either metformin or rosiglitazone during the preindex period and remained on monotherapy throughout the postindex period (Mono/Mono cohort), switched to dual therapy with both agents (Mono/Dual cohort), or switched to FDCT (Mono/FDCT cohort). Some subjects were receiving dual therapy with metformin and rosiglitazone during the preindex period and remained on dual therapy throughout the postindex period (Dual/Dual cohort) or switched to FDCT (Dual/FDCT cohort). A medication possession ratio (MPR)-a proxy measurement of medication adherence-was calculated for each subject for each period. Changes in medication adherence were compared using a general linear model.

RESULTS: Overall, data from the records of 16,928 subjects (8499 men, 8429 women; mean [SD] age, 58.12 [11.97] years) were included in this study. There was significantly less reduction in the MPR change for the Mono/FDCT cohort compared with the Mono/Dual cohort (-4.6% vs -12.4%; P < 0.001). There was significant improvement in the mean MPR change for the Dual/FDCT cohort compared with the Dual/Dual cohort (3.5% vs -1.3%; P < 0.005).

CONCLUSIONS: The results of this retrospective database analysis suggest that rosiglitazone-metformin FDCT yielded significant improvements in medication adherence rates compared with dual therapy regimens.