Solubility Enhancement of Simvastatin by Microwave Technology

Abstract

Simvastatin is a lipid-lowering drug with poor aqueous solubility and dissolution-limited oral bioavailability. The present investigation aimed to enhance the solubility and dissolution characteristics of Simvastatin by preparing inclusion complexes with ?-cyclodextrin (?-CD) and hydroxypropyl-?-cyclodextrin (HP?-CD). The complexes were prepared using physical mixture, kneading, and microwave irradiation techniques. Phase solubility studies were carried out to determine the complexation behavior and stability constants. Characterization of the complexes was performed using Fourier-transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). Phase solubility diagrams showed an AL-type profile indicating formation of 1:1 inclusion complexes with stability constants of 410 M?¹ for ?-CD and 727 M?¹ for HP?-CD. Dissolution studies revealed that microwave-prepared HP?-CD complexes significantly enhanced drug release compared with pure Simvastatin. The optimized formulation showed 92.4% drug release within 60 min, whereas pure drug exhibited only 31.8% release. Stability studies conducted at room temperature and accelerated conditions confirmed formulation stability. The results demonstrate that cyclodextrin complexation, particularly with HP?-CD, is an effective strategy for improving the solubility and dissolution rate of poorly water-soluble drugs.

Introduction

Poor aqueous solubility is a major challenge in oral drug delivery, especially for many modern drugs like Simvastatin, leading to low and inconsistent bioavailability. To overcome this, the study focuses on cyclodextrin inclusion complexation, a technique that improves drug solubility, dissolution rate, and stability by encapsulating hydrophobic drug molecules within a cyclodextrin cavity.

Among cyclodextrins, β-cyclodextrin and its derivative hydroxypropyl-β-cyclodextrin (HPβ-CD) are used due to their effectiveness in forming stable complexes. HPβ-CD offers better solubility and lower toxicity compared to β-CD.

The study aims to prepare and evaluate Simvastatin inclusion complexes using three methods: physical mixing, kneading, and microwave irradiation. Analytical techniques such as FT-IR, DSC, PXRD, and SEM are used to confirm complex formation and analyze physicochemical changes.

Experimental results, including phase solubility studies, show a significant increase in Simvastatin solubility with increasing cyclodextrin concentration, forming stable 1:1 complexes. Advanced preparation methods like kneading and microwave irradiation enhance interaction between drug and cyclodextrin, improving dissolution more effectively than simple physical mixing.

Overall, the study demonstrates that cyclodextrin-based inclusion complexes are an effective strategy to enhance the solubility, dissolution rate, and oral bioavailability of poorly water-soluble drugs like Simvastatin.

Conclusion

The present study successfully demonstrated that cyclodextrin inclusion complexation is an effective strategy for improving the aqueous solubility and dissolution characteristics of poorly water-soluble drugs such as Simvastatin. Inclusion complexes of Simvastatin were prepared using ?-cyclodextrin and hydroxypropyl-?-cyclodextrin through different preparation techniques including physical mixture, kneading method, and microwave irradiation method. Phase solubility studies confirmed the formation of 1:1 drug–cyclodextrin inclusion complexes, indicating effective molecular interaction between Simvastatin and the cyclodextrin carriers. The aqueous solubility and dissolution studies revealed a significant enhancement in drug solubility and dissolution rate following complexation, particularly in the case of the HP?-CD complexes. Among the different preparation methods evaluated, the microwave irradiation technique proved to be the most efficient method, producing inclusion complexes with superior solubility and dissolution performance. The improved dissolution behavior observed in the microwave-prepared complexes may be attributed to enhanced molecular interaction between the drug and cyclodextrin molecules, reduction in drug crystallinity, and improved wettability of the drug particles. Characterization studies including FT-IR spectroscopy, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) confirmed the successful formation of stable inclusion complexes and indicated partial transformation of the drug from a crystalline to an amorphous state. Stability studies conducted under both normal and accelerated conditions further demonstrated that the optimized formulation remained stable during storage. Overall, the results of the present investigation indicate that hydroxypropyl-?-cyclodextrin inclusion complexes prepared by microwave irradiation offer a promising formulation approach for enhancing the solubility and dissolution rate of Simvastatin. This strategy may ultimately lead to improved oral bioavailability and therapeutic efficacy of poorly water-soluble drugs.

References

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Copyright

Copyright © 2026 Mr. Zanwar Vijaykumar Jugalkishor, Ms. Kale Ajwita Satishrao , Mr. Deshmukh Amit Manohar , Mr. Pradeep Madhukar Jadhav . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.