The polymorph transformation screening of GMP entails the utilization of distinct methodologies, including neat grinding (NG), solvent drop grinding (SDG), and solvent evaporation (SE). The neat grinding procedure involves the grinding of 50 grams of GMP powder using a mortar and pestle for a duration of 30 minutes. In the solvent drop grinding technique, a similar amount of GMP powder, 50 grams, is subjected to grinding using a mortar and pestle for 10 minutes while simultaneously being dripped with acetone p.a. As for the solvent evaporation technique, 100 grams of GMP powder is dissolved in 100 ml of acetone p.a, stirred for 30 minutes until complete dissolution is achieved, and subsequently evaporated at ambient temperature to induce the recrystallization of GMP (Qiao et al. 2011).

The modified polymorph characterization of GMP involves the utilization of various analytical techniques, namely differential scanning calorimetry (DSC, STA PT1600, Linseis Thermal Analisis, Germany), powder X-Ray diffraction (PXRD, Bruker D8 Advance, USA), and scanning electron microscope (SEM, JEOL JSM-6360LA, Japan). Additionally, the performance evaluation encompasses the assessment of flow properties, compressibility index, solubility, and dissolution rate, which are compared with those of unmodified GMP.

Based on the characterization results, the best formulation for the modified polymorph of GMP was selected for the tablet formulation. Two formulations were prepared: the modified polymorph GMP tablet (MP) and the unmodified GMP tablet (NM), using the direct compression method with a tablet strength of 4 mg per 200 mg tablet weight (Table 1).

The evaluation of compacted mass encompasses several aspects, including flow properties, moisture content, compression ratio, and compressibility index. Additionally, tablet evaluation involves organoleptic assessment, size uniformity, hardness, friability, disintegration time, content uniformity, drug release rate determination, and dissolution testing.

Comparative in vitro dissolution tests were conducted on 12 tablets each of GMP MP and Amaryl®. The dissolution studies were performed using 900 mL of three different dissolution media: KCl/HCl buffer pH 1.2, acetate buffer pH 4.5, and phosphate buffer pH 6.8, all maintained at a temperature of 37.0 ± 0.5 °C. The USP type II dissolution apparatus with an agitation speed of 50 rpm was utilized. Samples of 10 mL were withdrawn at 10, 15, 30, 45, and 60 minutes and the contents of the active ingredient were analyzed using an ultraviolet-visible spectrophotometer (Shimadzu UV-1800, Japan) at a wavelength of 228 nm.

The results of the comparative in vitro dissolution test were expressed in terms of the similarity factor (f2), calculated using the following equation:

${\mathrm{f}}_2=50\times \log \left\{\left[1+\frac{1}{n}\sum _{t=1}^n (Rt-Tt{)}^2\right]\times 100\right\}$ (Equation 5)

F2 represents the similarity factor, Rt denotes the cumulative drug amount dissolved at each sampling time from the reference product, and Tt represents the cumulative drug amount dissolved at each sampling time from the test product (Badan Pengawas Obat dan Makanan 2022b; Satrialdi et al. 2011). A product is considered equivalent or exhibits a similar dissolution profile to the innovator product when the similarity factor falls within the range of 50 to 100.

The characterization and performance evaluation of the modified polymorphs of GMP was carried out through the transformation of GMP form I into form II using the techniques of neat grinding, solvent drop grinding, and solvent evaporation. The resulting modified polymorphs were subjected to characterization techniques including powder X-Ray diffraction (PXRD) for assessing diffraction patterns, differential scanning calorimetry (DSC) for analyzing thermal profiles, and scanning electron microscopy (SEM) for examining crystal habits. These characterization results were compared with existing literature data to confirm the polymorphic form of GMP. It is noteworthy that GMP exhibits two distinct polymorphic forms, namely form I and form II, with form II demonstrating higher solubility in water compared to form I (Bonfilio et al. 2011).

Fig. 1 presents the PXRD diffractograms of GMP Form I and Form II obtained from the literature (Bonfilio et al. 2011).

Figure 1. 

PXRD Difractogram of Forms I and II of GMP (Bonfilio et al. 2011).

Fig. 2 illustrates that in this study, GMP exists in form I (Bonfilio et al. 2011). The X-ray diffraction (XRD) patterns of the modified polymorphs of GMP obtained through neat grinding, solvent drop grinding, and solvent evaporation techniques are relatively similar to those of the non-modified GMP. This can be identified by the presence of five highest intensity peaks that exhibit comparable 2θ values, as indicated in Table 2.

Figure 2. 

PXRD Difractogram of Non-modified GMP [A]; Modified GMP with Neat Grinding GMP [B]; Solvent Drop Grinding [C]; Solvent Evaporation [D].

The modified polymorphs of GMP obtained through all three techniques did not undergo polymorphic transformation but rather exhibited a decrease in peak intensity interference. This phenomenon is referred to as amorphization (Brittain 2011, 2012; Giron 2001).

Fig. 3 depicts the DSC thermograms of GMP form I and form II. Both forms exhibit endothermic peaks above 200 °C, corresponding to their respective melting points. However, form II displays an additional exothermic peak around 140 °C, indicating a polymorphic transition from form II to form I (Bonfilio et al. 2011). This indicates that GMP form II is metastable, whereas GMP form I is physically stable (Endo et al. 2003).

Figure 3. 

DSC Termogram of Forms I and II of GMP (Bonfilio et al. 2011).

Fig. 4 illustrates that in this study, GMP exists in form I. The thermogram of DSC non-modified GMP shows an endothermic peak at 209.7 °C without an additional exothermic peak around 140 °C. The melting point of GMP in this study is concomitant with the literature (Bonfilio et al. 2011). The endothermic peak of a modified polymorph of GMP obtained through a neat grinding technique and solvent drop grinding is relatively similar to non-modified GMP. It is shown around 210.2 °C and 210.4 °C. However, the modified polymorph of GMP obtained through solvent evaporation exhibited a decrease in the endothermic peak at 203.3 °C. This phenomenon is referred to as amorphization. A solid exhibiting a high degree of crystallinity is typically characterized by a sharp and prominent endothermic peak in the DSC thermogram, indicating a high melting point. Conversely, an amorphous solid tends to display a lower melting point, often depicted by a gradual or less distinct endothermic peak in the DSC thermogram (Lee 2014).

Figure 4. 

Termogram DSC of Non-modified GMP [A]; Modified GMP with Neat Grinding GMP [B]; Solvent Drop Grinding [C]; Solvent Evaporation [D]

The crystal habit of GMP form I, as depicted in Fig. 5, appears irregular and forms agglomerates or clusters. In contrast, GMP form II exhibits a morphology resembling rods or needles.

Figure 5. 

SEM morphology of forms I and II of GMP (Bonfilio et al. 2011).

Fig. 6 illustrates that both the non-modified GMP and the modified polymorphs of GMP exhibit form I crystal habits, characterized by irregular agglomerates that interconnect due to their highly hydrophobic nature. However, in the morphology of GMP obtained through the solvent evaporation technique, a reduction in particle size is observed, which can have an impact on the solubility and dissolution rate of the compound.

Figure 6. 

SEM morphology of non modified GMP [A]; modified GMP with neat grinding GMP [B]; solvent drop grinding [C]; solvent evaporation [D].

Based on the comprehensive characterization using PXRD, DSC, and SEM techniques, it was observed that the modified polymorphs of GMP obtained through the three different methods did not undergo a polymorphic transformation from form I to form II, but rather exhibited amorphization. Notably, the solvent evaporation technique showed the most prominent amorphous characteristics. These findings highlight the absence of polymorphic changes in GMP and the significant impact of amorphization on its physicochemical properties.

The subsequent performance evaluation aimed to identify the most effective technique for polymorph modification of GMP, specifically in terms of its physical and chemical performance. This evaluation encompassed various parameters, including flow properties, compressibility index, solubility, and dissolution rate, which were compared to those of the non-modified GMP. Notably, the results presented in Table 3 indicate that the modified polymorphs of GMP obtained through the solvent evaporation technique exhibited the most favorable physicochemical performance. The solvent evaporation technique involved the dissolution of GMP at the molecular level, followed by recrystallization, leading to the amorphization of the compound (Giron 2001). This amorphization process had significant implications for the flow properties, compressibility index, particle size, and ultimately the mechanical properties, solubility, and dissolution rate of GMP (Censi and Di Martino 2015). Overall, the solvent evaporation technique demonstrated superior performance in enhancing the physicochemical properties of GMP for tablet formulation.

Despite the absence of polymorphic transformation of GMP from form I to form II, the performance evaluation demonstrated enhanced physical and chemical properties, encompassing flow properties, compresibility index, solubility, and dissolution rate, particularly in the modified polymorphs of GMP obtained through the solvent evaporation technique. These findings serve as a foundation for the formulation of GMP into tablet dosage forms.

The formulation of these tablets employed simple excipients, including amprotab as a disintegrant, avicel PH 102 as a filler, magnesium stearate as a lubricant, and talc as a glidant. The objective was to compare the tablet characteristics of GMP-modified polymorphs against tablets containing non-modified GMP, through the evaluation of compaction properties and final product attributes.

Tables 4 and 5 present the results of the compaction evaluation and the assessment of the finished product (tablet) characteristics for both non-modified and modified polymorphs of GMP. The compaction evaluation comprises assessments of flow properties, moisture content, compression ratio, and compressibility index. The tablet evaluation encompasses organoleptic properties, size uniformity, hardness, friability, fricsibility, disintegration time, content uniformity, assay, and dissolution rate.

Based on the evaluation of tablet bulk properties (Table 4), the tablets containing GMP with modified polymorphs meet the criteria for direct compression due to their favorable flow properties and compressibility compared to the tablets containing non-modified GMP. This can be attributed to the amorphization process that occurs during the modification of GMP polymorphs using the solvent evaporation technique, leading to the transformation of the GMP solid into a fine and lightweight form.

The evaluation results of the tablets (Table 5) containing modified polymorphic GMP and non-modified GMP met the specified criteria, although the non-modified GMP tablets exhibited lower performance, particularly in terms of content uniformity and drug content. This can be attributed to the fine and agglomerated nature of the non-modified GMP raw material, resulting in challenges in achieving homogeneity during the blending process with other excipients (Darusman et al. 2021).

Fig. 7 illustrates the dissolution profiles of the modified polymorphic GMP tablets, demonstrating a significant increase in the percentage of drug dissolved compared to the non-modified GMP tablets. The dissolution rate at 60 minutes for the modified polymorphic GMP tablets exhibited a substantial enhancement of 98.82 ± 0.86% compared to the non-modified GMP tablets, which displayed a dissolution rate of 56.35 ± 0.43%.

Figure 7. 

Dissolution profile comparison curve of non-modified GMP tablet [FI] and GMP-modified tablet polymorph (FII).

GMP exists in two polymorphic forms, namely form I and form II, with form II exhibiting higher solubility in water (Bonfilio et al. 2011). The polymorphic form of an active pharmaceutical ingredient (API) demonstrates distinct physicochemical properties such as density, solubility, optical properties, and mechanical behavior. These properties influence the mechanical properties or manufacturability, as well as the dissolution rate and bioavailability of the API (Zhang et al. 2013).

FII refers to a tablet formulation containing GMP with modified polymorphs obtained through the solvent evaporation technique. In the solvent evaporation process, GMP powder undergoes dissolution at the molecular level, followed by recrystallization at room temperature. This process leads to amorphization, which subsequently impacts the solubility and dissolution rate of the drug (Giron 2001; Gozali et al. 2014).

Comparative in vitro dissolution testing was conducted on GMP modified polymorph tablets as a preliminary assessment for bioequivalence, comparing them to the reference innovator drug Amaryl® at a 4 mg dose. The dissolution testing was performed at three different pH levels (1.2, 4.5, and 6.8) to simulate gastrointestinal conditions. The similarity between the dissolution profiles of the test and reference products was evaluated using the similarity factor (f2), and the obtained values fell within the acceptable range of 50–100 (Badan Pengawas Obat dan Makanan 2022b).

The comparative in vitro dissolution profiles of the GMP-modified polymorph tablets and Amaryl® in different dissolution media were assessed through Figs 8–10. The f2 values for the KCl/HCl buffer pH 1.2 dissolution test did not meet the acceptance criteria of 50–100, with a value of 45.15 ± 0.23. This deviation can be attributed to the %CV exceeding 10% for each time point. However, for the dissolution tests conducted in acetate buffer pH 4.5 and phosphate buffer pH 6.8, the f2 values were within the acceptable range of 50–100, specifically 60.15 ± 0.27 and 88 ± 0.35, respectively. Consequently, it can be concluded that the GMP-modified polymorph tablets are dissimilar to the innovator product, Amaryl®. The requirements for comparative in vitro dissolution testing mandate that the test and reference products are considered similar if their f2 values fall within the range of 50–100 for the three pH conditions (pH 6.8, 4.5, and 1.2).

Figure 8. 

Dissolution profiles of the test and reference products in phosphate buffer pH 6.8.

Figure 9. 

Dissolution profiles of the test and reference products in citrate buffer pH 4.5.

Figure 10. 

Dissolution profiles of the test and reference products in KCl/HCl buffer pH 1.2.

Considering GMP’s pKa value of 6.2, it is established that GMP undergoes increased ionization at pH levels above its pKa (Darusman and Rahayu 2017). This enhanced ionization renders GMP more polar in nature, thereby leading to improved solubility and dissolution rate (Darusman and Siti M 2017). The modification of GMP’s polymorphs aimed to enhance its solubility and dissolution rate without undergoing a transformation from form I to form II; rather, the amorphous state was achieved (Giron 2001). This elucidates the dissimilarity observed in the f2 value at pH 1.2.