Effects of hospital generic drug substitution on diabetes therapy

Objectives: To evaluate the effects on physicians' prescribing behavior and on the therapeutic outcome of non-insulin-dependent diabetes patients of substituting different generic brands of metformin. Methods: We adopt a retrospective cohort study involving 280 type-2 diabetes patients who regularly used the outpatient services of one medical center and who had changed metformin brands five times between 2003 and 2008. The aim was to examine the effects of switching brands. The generalized estimating equation was used to determine whether drug brand switching affected patient glycated hemoglobin A_1c (HbA_1c) levels, their prescribed daily dose, or their adherence to medication with metformin. Results: HbA_1c levels increased from 7.91 to 8.34 throughout the study period, although it was found that brand switching did not adversely affect HbA_1c levels after controlling for patient characteristics and the time course of the study. Furthermore, the prescribed daily dose of metformin was stable throughout the study period, and was approximately 0.8 of the defined daily dose. Finally, although adherence was significantly higher with the original metformin than with the four generic brands, patients still maintained high levels of adherence of >0.8. Conclusion: Although switching between different brands of metformin slightly affected the prescribing behavior of the physicians, there was no unfavorable effect on patient HbA_1c levels. Thus, the policy of substituting between different generic brands of metformin is a good cost-effective approach that does not adversely affect the quality of diabetes patient care.