Identification of the Glimepiride and Metformin Hydrochloride Physical Interaction in Binary Systems

Glimepiride is often combined with metformin HCl as an oral antidiabetic in type II diabetes mellitus, which provides a complementary and synergistic effect with multiple targets for insulin secretion. Glimepiride includes class II of BCS, which solubility practically insoluble in water but high permeability, which will impact the drug's small bioavailability. In contrast, metformin HCl includes class III of BCS, which has a high solubility in water, but low permeability is absorbed approximately 50-60% in the digestive tract given orally. The co-crystallization method can be used to improve the glimepiride solubility properties and the permeability properties of metformin HCl by interrupting glimepiride with metformin HCl physically. This study aims to identify the physical interactions between glimepiride and metformin HCL using a thermal analysis of Differential Scanning Calorimetry (DSC) and then confirmed by a computational approach. Identifying the physical interactions between glimepiride and metformin HCL was carried out by plotting the melting points generated from the endothermic peaks of the DSC thermogram at various compositions versus the mole ratios of the two were further confirmed by the computational approach using PatchDock. The results of the phase diagram analysis of the binary system between glimepiride and metformin HCl show a congruent pattern, which indicates the formation of co-crystal or molecular compounds at a 1 : 1 mole ratio at 228°C. Computational approach results showed that the interaction between glimepiride and metformin HCl did not form new compounds but heterosinton formation that was stable in molecular dynamics simulations.


INTRODUCTION
class II, which has low solubility but high permeability with practically insoluble solubility data in water, so that it will have an impact on the small bioavailability of the drug. In contrast, MET includes in BCS class III, which has a high solubility in water, but has low permeability, which is about 50-60% absorbed in the gastrointestinal tract given orally 2, 3 .
Sanofi Aventis has produced GMP and MET in a fixeddose combination (Amaryl M®) tablet dosage form, which is an innovator product 4 . However, some pharmaceutical manufacturers that make copy product of GMP and MET are constrained in producing tablet preparations that meet quality requirements so that efforts need to be made to increase the solubility of GMP as well as the permeability of MET by physically interacting GMP with MET through the cocrystallization method 5, 6 . Cocrystallization is a physical method based on the combination of active pharmaceutical ingredients acting as a host with co-formers acting as guests through hydrogen bonds or Van der Waals in the same crystal Studies on the identification of the type of interaction between GMP and MET have not been previously reported. For this reason, it is necessary to identify the physical interactions that occur between GMP and MET using thermal analysis differential scanning calorimetry (DSC), the results of which are then constructed in the form of a phase diagram of the GMP-MET binary system 9, 10 . Furthermore, the resulting physical interactions were confirmed by the computational approach using docking simulations methods, molecular dynamics simulations, and MM/PBSA binding-free energy calculations 11,12 .

Materials
The material used were glimepiride (Glenmark, India) and metformin hydrochloride (Hildose, India

Molecular structure modeling and optimization
The molecular structure of GMP and MET was modeled in two-dimensional using the BIOVIA Discovery Studio

Glimepiride-metformin complex formation simulations
The optimized GMP and MET compounds were then simulated for complex formation. This complex formation simulation was accomplished using the PatchDock web server according to the procedure reported by Fakih et al 15 .

Identification of glimepiride-metformin interactions
The molecular interactions formed between GMP and MET molecules were then identified using the BIOVIA

Glimepiride-metformin interaction dynamics
Interaction dynamics simulations were performed using Gromacs 2016.3 to observe and identify the stability of GMP and MET. Electrostatic forces were selected using the Particle Mesh Ewald method. Neutralization of the system was carried out by adding Na + and Clions.
Solvation was determined using the TIP3P water model.
The simulation preparation stage includes minimization, heating to 310 K, temperature equilibration, pressure equilibration, and a 500 ns production run with a 2 fs timestep 15, 16 .

MM/PBSA end-point binding-free energy calculations
The

Preparation of glimepiride-metformin physical mixtures
Preparation of the physical mixture of GMP-MET was carried out by weighing GMP and MET at various compositions based on the mole ratio between the two, which was carried out for three replications. It was known that the molecular weights of GMP and MET were 490.62 g/mol and 165.63 g/mol, respectively.
Furthermore, thermal analysis was carried out using the DSC method to obtain the melting point of the endothermic peak of the DSC thermogram, which was constructed into a phase diagram of the GMP-MET binary system 21 .

Glimepiride-metformin binary mixtures
Preparation of the GMP-MET binary mixture aims to identify the interactions between GMP and MET at various compositions based on their molecular ratios, whether the cocrystal phase (molecular compound) or a simple eutectic mixture was formed as well as its molecular ratio, as shown in Table I. This binary mixture was thermally analyzed using the DSC method so that the melting point from the endothermic peak of the DSC thermogram was obtained, as presented in Table II.
Then, it was constructed into a binary system phase diagram by plotting the resulting melting points of the endothermic peak of the DSC GMP-MET thermogram at various compositions versus the mole ratio of the two, as presented in Figure 2.
The results of the phase diagram analysis of the GMP-

Computational approach of glimepiride-metformin
The computational approach was demonstrated to identify and confirm the physical interactions between GMP and MET. Figure 3 shows that the interaction between GMP and MET did not form new compounds.
However, the interaction that occurs was the formation of hydrogen bonds with heterosinton formation (Table   III)

DATA AVAILABILITY
All data are available from the authors.