Inclusion Compound of Efavirenz and γ-Cyclodextrin: Solid State Studies and Effect on Solubility

Area of Science:

• Pharmaceutical Sciences
• Drug Delivery Systems
• Supramolecular Chemistry

Background:

• Efavirenz is a crucial antiretroviral medication for Human Immunodeficiency Virus type 1 (HIV-1) infections.
• Poor aqueous solubility of efavirenz necessitates oil-based excipients in pediatric liquid formulations.
• Improving efavirenz solubility is key for developing more effective and patient-friendly drug delivery systems.

Purpose of the Study:

• To investigate the interaction between gamma-cyclodextrin and efavirenz in aqueous solution and solid state.
• To determine the optimal host-guest stoichiometry for efavirenz-cyclodextrin complex formation.
• To characterize the solid inclusion compound and evaluate its impact on efavirenz solubility.

Main Methods:

• Solution studies utilized the continuous variation method with 1H NMR to determine host-guest stoichiometry.
• Solid inclusion compounds were prepared via co-dissolution followed by freeze-drying.
• Solid-state characterization employed FT-IR, 13C{1H} CP-MAS NMR, thermogravimetry, and X-ray powder diffraction.

Main Results:

• A preferential host-to-guest stoichiometry of 3:2 (gamma-cyclodextrin to efavirenz) was identified in aqueous solution.
• Solid inclusion compounds were successfully prepared and characterized, confirming the 3:2 stoichiometry as optimal for pure compound isolation.
• The study established the effect of gamma-cyclodextrin complexation on efavirenz solubility using the isotherm method.

Conclusions:

• Gamma-cyclodextrin forms inclusion complexes with efavirenz, significantly impacting its properties.
• The 3:2 stoichiometry is critical for obtaining a pure solid inclusion compound.
• This research provides a foundation for developing improved efavirenz formulations with enhanced solubility and potentially better therapeutic efficacy.