Parenteral Depot System Of Huperzine A For The Treatment Of Alzheimer's Disease

Huperzine A is available currently in the market twice daily as tablet or capsule (200 to 400μg/day). Though this daily repeated oral administration is convenient for most of patients, it is difficult for AD patients who suffer memory disorder, not to miss scheduled self-medication. Gastrointestinal side effects were also reported, such as, nausea and anorexia, so long term and non-gastrointestinal formulations of huperzine A or other drugs against AD are attractive for researchers. A once-a-week transdermal delivery system of huperzine A was reported, but the complication of human skin may impact the release rate, which depended on the permeability of drug in human skin, and may vary from one to another, resulting in a variation in plasma concentration and efficacy. In this study, the preparation, characterization, pharmacokinetics, relationship between the in vitro and in vivo releases of microspheres delivery system consisting of huperzine A and various Poly (D, L-lactide-co-glycolide) (PLGA) polymers using O/W solvent evaporation technique were described.1. IntroductionThe definition of biodegradable polymers was given. Among various biodegradable polymers, polylactic acid (PLA) and its copolymer with glycolic acid, poly(d,l-lactic acid-co-glycolide) (PLGA) are a well proven class in safety. PDS in form of microspheres are by definition spherical devices to allow subcutaneous or intramuscular injection in suspension using conventional syringes. Solvent evaporation technique to prepare microspheres was also described. Huperzine A is an acetylcholinesterase inhibitor, which can effectively inhibit acetylcholinesterase.2. Preparation and characterization of huperzine A loaded microspheres with a mechanical stirringHuperzine A loaded PLGA microspheres were prepared by an oil/water (o/w) solvent evaporation technique. Effects of polymer concentration, drug content, ratio of o/w, PVA concentration, temperature, emulsification speed etc. on encapsulation efficiency, particle size and in vitro release were investigated. For example, with a decrease of the ratio of o/w from 1 : 100 to 1 : 50, the encapsulation efficiency was reduced about 4%. Increasing the PVA concentration from 0.5% to 2% reduced the percentage encapsulation efficiency of huperzine A from 60.7% to 47.4% and the particle size of microspheres from 84.2 to 26.2μm. In vitro release showed a low initial burst followed by a smooth sustained release up to 12 or 14 days. The addition of stearic acid improved the encapsulation efficiency, but also accelerated the in vitro release of hupezine A from microspheres. An increased actual drug loading also led to a rapid in vitro release. After i.m. administration of huperzine A loaded microspheres in mice, huperzine A was sustained released from the PLGA microspheres up to 12 days with a low initial burst. A good linear regression relationship was observed between the in vitro and in vivo releases.3. Removal of residual solvent in the PLGA microspheresOrganic solvent such as dichloromethane is widely used for the preparation of PLGA microspheres. Removal of residual solvent to very low concentrations is important to ensure a safe and stable microspheres product. The ICH guidelines have prescribed a limit of 600 ppm for dichloromethane in pharmaceuticals. However, the solvent was difficult to remove and a number of studies including evaporation and extraction to reduce the organic solvent levels in polymeric microparticles have been reported. In this study, by the programmed heating in vacuum, the residual dichloromethane was reduced from 40,000 to 180 ppm in the PLGA microspheres without significant effects on the properties of the microspheres.4. Preparation and characterization of huperzine A loaded microspheres with a homogenizerDifferent phenomenon was found when a homogenizer was used in the emulsion process of the preparation of the huperzine A loaded microspheres. When the homogenization rate was increased from 1000 rpm to 2000 rpm, the particle size was reduced about sextuple but the encapsulation efficiency was decreased only about 7%. PLGA 502H/503H (1 : 1) microspheres with an in feed drug/polymer ratio of 5% were prepared by homogenization. With the same particle size of microspheres, the encapsulation efficiency was about 10% lower than that by a mechanical stirring. Though the shear power of homogenizer was stronger, which led to rapid decrease of particle size of the microspheres with the increase of the homogenization rate, it agitated the aqueous phase less vigorously, and therefore the solidification of microspheres was slowed, resulting in the decreased encapsulation efficiency.5. Pharmacokinetics of huperzine A loaded microspheres administrated via intramuscularly and subcutaneously routes to dogsAt present, many biodegradable poly(lactic-co-glycolic acid) PLGA depot products, especially microspheres or microparticles, containing various drugs become commercially available. Among these products, some were intended as intramuscular (i.m.) injection, such as Risperdal Consta (risperidone), Sandostatin LAR (octreotide acetate), Lupron depot (leuprolide acetate), Trelstar LA and Trelstar depot (triptorelin pamoate). Others were given as subcutaneous (s.c.) injection, for example, Nutropin Depot (human growth hormone) and Zoladex (goserelin acetate). Though enormous studies on these products and other sustained release systems were reported, the investigation on the differences of plasma concentration-time profiles of these products administrated via i.m. and s.c. routes has been reported rarely. In this study, one kind of huperzine A loaded microspheres (single dose) were injected intramuscularly (i.m.) or subcutaneously (s.c.) to five beagle dogs respectively. It was found that after s.c. injection, the release of huperzine A from microspheres was faster than that after i.m. injection.6. In vitro/in vivo correlation of huperzine A loaded microspheres in dogsWhile the FDA In vitro/in vivo correlation (IVIVC) guidance is applicable only to oral dosage forms, the principles of this guidance can be used to develop IVIVC for non-oral products. However, few examples were given where in vitro dissolution in PBS can accurately predict the in vivo release profile for parenteral biodegradable depot systems and therefore, ongoing research is necessary in developing in IVIVC for these types of products. In this study, three kinds of huperzine A loaded microspheres (single dose) were injected intramuscularly (i.m.) or subcutaneously (s.c.) to five beagle dogs respectively. With the increase of the PLGA molecular weight and the particle size, the in vivo an in vitro release periods of huperzine A was prolonged. The IVIVC models of huperzine A were established successfully between the in vitro releases and the in vivo releases of huperzine A loaded PLGA microspheres. It could be explained by the diffusion-controlled sustained-release of huperzine A from PLGA microspheres combined with a rapid in vivo absorption of huperzine A. A better linearity was observed after i.m. administration than that after s.c. administration. It was also found that the values of correlation coefficient of the smaller microspheres were higher than these with a larger particle size.