Category: Formulation and Quality
Purpose: Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive, memory loss and various neuropsychiatric symptoms. Donepezil is a reversible, noncompetitive and selective cholinesterase inhibitor used to treat AD. Cholinesterase inhibitors slow down the degradation of acetylcholine in the synaptic cleft and compensate for its deficiency. However, most patients need help taking medication for a variety of reasons, such as a lack of understanding of the instructions, forgetfulness, or disruption of everyday life. The purpose of this study was to prepare donepezil poly(lactic-co-glycolic acid) (PLGA) microparticles with sustained release of donepezil for one month using new microparticle drug delivery systems (IVL-PPFM®, microfluidic-based microparticle fabrication method), to evaluate its physicochemical characteristics and to investigate the pharmacokinetic characteristics in the beagle model.
Methods: Various formulations of donepezil-loaded PLGA microparticles were prepared by IVL-PPFM® based on microfluidic system. Since the type of polymer and the polymer-drug ratio affect the drug residence time, various formulation studies have been conducted to obtain sustained release injections for one month.
To prepare donepezil-loaded PLGA microparticles, 0.33 g donepezil and 3 g PLGA were dissolved in 17 g of dichloromethane (DCM) and an aqueous phase containing 0.25 % polyvinyl alcohol (PVA) as emulsifier was prepared. And monodisperse microspheres containing donepezil were prepared after injecting donepezil based biodegradable polymer solution and aqueous solution into the microchannel. The drug retention period was controlled using a biodegradable polymer of 75/25 DL-lactide/glycolide copolymer (ester or carboxylic acid terminated) and a polymer mixture of Poly(DL-lactide)+75/25 DL-lactide/glycolide copolymer (carboxylic acid terminated) (1:1). Polymer-drug ratios have also been considered to control the drug release time. The higher the proportion of polymers, the longer the drug retention time. Then, 4% mannitol solution was added to microparticles as a lyoprotectant before freeze drying. After preparing the microparticles using IVL-PPFM® method, the surface morphology of the microparticles was observed by scanning electron microscopy (SEM) and the size distribution was measured by a laser particle size analyzer (PSA). About 200 mg of microparticles were dissolved in 200 mL acetonitrile (0.1 mg/mL donepezil concentration), and drug loading of microparticles was determined by separation of the donepezil from an aqueous medium containing drug by HPLC.
For determination of pharmacokinetic characteristics, beagle dogs were subcutaneously injected with 2 mL suspensions of 191.5 mg (2:1, polymer-drug ratio), 319.2 mg (4:1), 638.4 mg (9:1) of donepezil-loaded 75/25 DL-lactide/glycolide copolymer (carboxylic acid terminated) microparticles (as 63.84 mg of donepezil, 50 % of 28 days oral dose) on the first day of the experiment. The reference beagle dog group was orally administered with 5 mg of donepezil HCl tablet once daily for 3 days. In addition, 75/25 DL-lactide/glycolide copolymer (ester terminated) and polymer mixture of Poly(DL-lactide)+75/25 DL-lactide/glycolide copolymer (carboxylic acid terminated) (1:1) were used to prepare microparticles to investigate the drug release effects of polymer to drug ratio of 4:1. Those microparticles were injected in beagle dogs to confirm the duration of drug release time for one month.
Results: The optimized PLGA microparticles were characterized in terms of particles size, size distribution, morphology and drug loading. Unlike conventional method such as solvent evaporation or gas spraying, the particle size distribution of the prepared PLGA microparticles by IVL-PPFM® was controlled narrow and uniform with a median diameter (D50) of 40.84~45.64 μm and a width of 15.88~18.69 μm. The surface of these mannitol-coated microparticles observed by SEM was smooth and nonporous. The drug content measured according to the formulations of donepezil-loaded microparticles was 84.86~95.18 %.
In the pharmacokinetic study using beagle dogs to confirm the maintenance of the plasma concentrations for one month, it was confirmed that the plasma concentrations of donepezil were maintained for 28 days without initial burst only with single donepezil-loaded microparticle injection in the case formulation of 75/25 DL-lactide/glycolide copolymer (carboxylic acid terminated) and 9:1 polymer-drug ratio. The value of AUClast (area under the plasma concentration-time curve from time zero to time of last measurable concentration) was 886.87 μg∙h/L, the AUC of test/reference ratio was 104.00 %. The value of Cmax (maximum plasma concentration) was 3.68 μg/L and the Cmax of test/reference ratio was 81.24 %. AUClast and Cmax of the microparticles with only single injection showed similar results to multiple administration of the reference orally dosed drug of half the one-month dose.
Conclusion: A new microparticulate drug delivery system, IVL-PPFM® was introduced. Donepezil-loaded microparticles made by IVL-PPFM® showed better physicochemical characteristics, such as controllable particle size, monodisperse size distribution and smooth surface morphology, as well as better pharmacokinetic characteristics, such as higher pharmacokinetic area under the curve, stable low-dose without initial burst and long-acting profile. In conclusion, we found a formulation that could be sustained for one month with only single donepezil-loaded microparticles injection of half a month oral medication by changing the drug delivery route in beagle dogs and these results demonstrate the potential use of donepezil-loaded microparticles for long-term AD treatment.