Pharmacokinetics of a fixed-dose glimepiride/sustained-release metformin combination

Pharmacokinetic (PK) profiles of glimepiride and metformin have been established for the combination drug as well as each agent individually. However, the PK profiles of a combination drug containing glimepiride and sustained-release (SR) metformin have not been reported. To compare the pharmacokinetic profiles of glimepiride/SR metformin (2 mg/500 mg) with the PK of immediate-release (IR) formulations, an open-label, randomized, 3-period, 3-sequence, 3-treatment, crossover study was conducted in 12 healthy subjects.

After a single administration of glimepiride/SR metformin 2 mg/500 mg (Treatment) or glimepiride/metformin IR 2 mg/500 mg (Reference 1), or administration of 2 doses of glimepiride/metformin IR 1 mg/250 mg 12 h apart (Reference 2), serial blood samples were collected and drug concentrations determined by liquid chromatography/ tandem mass spectrometry. PK parameters (Cmax and AUC24) for glimepiride and metformin were log-transformed and compared using a mixed-effects model analysis of variance (ANOVA). The mean differences and 95% confidence intervals (CIs) were back-transformed to obtain geometric mean ratios along with the CIs for the ratios.

Treatment demonstrated similar systemic exposures for glimepiride; the geometric mean ratio (95% CIs) for glimepiride AUC24 was 1.05 (0.97 - 1.13) for Treatment relative to Reference 1 and 1.08 (1.00 - 1.17) for Treatment relative to Reference 2. The SR formulation showed a delay in the time to reach maximum concentration for metformin from 1.0 - 4.0 h to 4.0 - 8.0 h and a decreased AUC24 value; the geometric mean ratio for metformin AUC24 was 0.87 (0.74 - 1.03) for Treatment relative to Reference 1 and 0.75 (0.63 - 0.88) for Treatment relative to Reference 2.

This study demonstrates for the first time that fixed-dose glimepiride and SR metformin 2 mg/500 mg shows a PK profile similar to that of glimepiride, but with a delayed time to maximum concentration and slightly decreased bioavailability for metformin compared with the IR fixed-dose combination, in healthy volunteers. PK profiles from this exploratory study will be helpful in designing and conducting further studies in diabetic patients.