Spectroscopic Characterization Using 1H and 13C Nuclear Magnetic Resonance and Computational Analysis of the Complex of Donepezil with 2,6-Methyl-β-Cyclodextrin and Hydroxy Propyl Methyl Cellulose

Donepezil (DH), a selective acetylcholinesterase inhibitor, is widely used to manage symptoms of mild to moderate Alzheimer's disease by enhancing cholinergic neurotransmission and preventing acetylcholine breakdown. Despite the effectiveness of oral formulations, extensive hepatic metabolism and low systemic bioavailability have driven the search for alternative delivery systems. This study focuses on nasal delivery as a non-parenteral substitute, utilizing hydroxypropyl methylcellulose (HPMC) for its mucoadhesive properties and methyl-β-cyclodextrin (Me-β-CD) for its ability to enhance permeability and form inclusion complexes with drugs. Prior studies demonstrated the potential of HPMC-based nasal films for nose-to-brain delivery of donepezil and highlighted Me-β-CD's role in improving drug solubility. Building on this, transparent gel formulations containing DH, HPMC, and 2,6 Me-β-CD were developed to investigate molecular interactions within two- and three-component systems. This study utilized a combination of nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) to provide detailed insights into the interactions between DH, 2,6-Me-β-CD, and HPMC. The findings provide critical insights into drug-excipient interactions, aiding the optimization of stability, solubility, and controlled release. This advances the rational design of nanotechnology-based drug delivery systems for enhanced therapeutic efficacy.