Assessments of Therapeutic Equivalence and Pharmacoeconomics of Original-Brand and Generic Drug of Glimepiride (Amaryl® vs. Glimepiride [Tanabe])

Abstract

Objective: The use of generic drugs is promoted for the purpose of reductions of medical costs and patient’s copayment.  In general, it is thought that clinical effects of the original brand and the generic drugs are equal if they are bioequivalent.  However, it is necessary to inspect their therapeutic equivalence to use the generic drugs securely.  We, therefore, assessed the therapeutic equivalence and pharmacoeconomics by substitution of an original drug (Amaryl®) with a generic drug (Glimepiride [Tanabe]).
Methods: Therapeutic Equivalence: The total variation was calculated by using the HbA1c levels before it switched from Amaryl® to Glimepiride [Tanabe].  The tolerance limits were set as 1/4 of the total variation.  Pharmacoeconomics: The difference of drug prices and the difference of patient’s copayment were calculated.
Results: As the variation of HbA1c levels was within tolerance limits before and after switching from Amaryl® to Glimepiride [Tanabe], we evaluated that their therapeutic effect was equivalent.  The difference of drug prices after switching from the original to the generic one was 4,582.6 yen/year on average (minimum: 949.0 yen, maximum: 12,045.0 yen); the difference of patient’s copayment was 872.5 yen/year on average (minimum: 0 yen, maximum: 3,613.5 yen).  These data show that the use of the generic drugs is effective to reduce medical costs.
Conclusion: For further promoting the use of the generic drugs, we consider it essential to compare the therapeutic equivalence and the safety of the original and the generic drugs in clinical practice.