Study On Preparation And Pharmacokinetics Of Oxybutynin Chloride Ethosomal Gel

BackgroundTransdermal drug delivery system has received more and moreattention for its unique superiority, the application of carriers technologyhave been focused on this systems development for enhancing transdermalflux. OXB is the common drug available for the treatment of Overactivebladder （OAB）. Oxybutynin transdermal gel （OTG） were approvedon January23,2009by FDA，this common gel is the only drug availablefor the treatment of OAB in a transdermal formulation.Transdermal flux of1g OTG once daily is improved by high dose （10%,W/W）,highconcentration of ethanol（70%,W/W）,and regulating pH（5.5）,to obtainthe clinical treatment efficacy. Therefore,Selecting OXB as a hydrophilicmodel drug, we designe a OXB ethosomal gel using ethosomes as theenhancing permeation carrier, to roduce drug and ethanol concentrationand improve transdermal flux of OXB across the skin and bioavailability.ObjectiveBased on OXB’high hydrophilicity、 low lipophilicity,and lowtransdermal permeability. For this reason, we designed a OXB transdermalsystem using ethosomes as the enhancing permeation carrier and prepare OXB ethosomal gel,to roduce drug and ethanol concentration,as a result,the delivery of OXB across the skin and bioavailability are enhanced sothat the clinical treatment efficacy can be obtained.Method1.Investigation solubility,octanol/water partition coefficient andtransdermal permeation of OXB.2.Establish entrapment efficiency methods and in vitro transdermaldetermination methods of OXB ethosomes by HPLC; Establish leveltransdermal diffusion cell penetrant （rats skin） inspection methods, todetermine transdermal flux of OXB through rat skin in vitro．3.OXB ethosomes were prepared by ethonal infusion andhomogenization method，based on single factor,orthogonal method wasinvestigated to screen the optimal formulation of the preparation, usingaccumulation permeation as a main evaluation index, while EE and D95asa reference index.4.The drug entrapment efficiency was determined by dialysismethod,the size distribution and zeta potential were determined byDLS,SEM and TEM were employed to determine ethosomes shape, thepreliminary stability of OXB ethosomes storage under4℃were studied.5.HPC was used as gel base, OXB ethosomal gel and OXB gel werefinally prepared; In vitro skin permeation of OXB ethosomal gel and gelwere studied using Franz diffusion cells，the Steady-state penetration rate, accumulation permeation and accumulation percentage were calculated.6.According to the guidance principle of preparation quality standardin Ch.P2010Volume Ⅱ, the preliminary stability and quality includingappearance,pH,viscosity and assaying,as well as cumulative permeatedpercentage were studied.7.Establish HPLC-MS method to determine the content of OXB inplasma,pharmacokinetics were investigated for percutaneous permeationof OXB ethosomal gel and gel in rabbits.Result1.OXB had the maximum solubility in30%（W/W）ethanol;theoctanol/water partition coefficient was0.070,with its logKo/wvalue at-1.16,and the human skin permeability coefficient of OXB was predictedas6.60×10^-10；The rat skin permeability coefficient of OXB obtained bylevel transdermal diffusion cell was8.9×10-8.Make sure that OXB be usedas a hydrophilic model drug for study of ethosomes.2.The concentration of OXB in the receptor compartment wasdetermined by HPLC.The equation for the calibration curve was A＝2.156×10³C＋6.246×10³，r＝0.9999，with a good linear relationshipbetween its concentration of0.5～800μg/ml, Recovery rate were between98-102%,within-day and between-day are below2%.3.The Orthogonal method shows that the ethosomal systems wascomposed of3%of phospholipid，45%of ethanol and5%of drug,while maintaining the emulsification temperature at30℃, with the secondemulsification for60min under continuous stirring.4.The average size was（58±12）nm, the entrapment efficiency andthe drug loading of the ethosomes were（49.9±1.0）％,（31.4±0.98）％respectively. The transdermal flux OXB from ethosome were5.4、39.4and49.5times higher than that from physical mixture,ethanol solution and45％（W/W）ethanol solution respectively at the same concentration,thepreliminary stability showed that the average size and entrapmentefficiency remained constant, the vesicular structure of the ethosomespersisted after a half year of storage under4℃.5.1%HPC was used as gel base to prepare OXB ethosomal gel;Different pH value have no effects on in vitro skin permeation ofethosomal gel compared with gel; The cumulative permeated percentagefrom ethosomal gel（4%OXB） were3.9times higher than that from gel（10%OXB）.6.The content of OXB ethosomal gel were determined by HPLC.Theequation for the calibration curve was A＝2.0755×10³C＋1.3003×10⁴，r＝0.9998，with a good linear relationship between its concentration of10～1000μg/ml,Recovery rate were between98～102%,within-day andbetween-day were below2%; The preliminary stability showed that theappearance,pH,viscosity and assaying,as well as cumulative permeatedpercentage of OXB ethosomal gel remained constant. 7.OXB in plasma was determined by HPLC-MS. The equation for thecalibration curve was A_i/A_s=0.0039C_i＋0.0078，r=0.9973，with a goodlinear relationship between its concentration of1～100ng/ml,Recoveryrate were between85-115%,within-day and between-day were below15%;Dose of OXB for20mg in the ethosomal gel and for50mg in the geltransdermal delivery for96h, the AUC_0�'96of ethosomal gel and gel were606.67ng/ml*h、516.40ng/ml*h，C_maxwere27.93ng/ml、29.81ng/ml，and t_maxwere6.67h、4.47h respectively.ConclusionOn the base of study of physico-chemical property of OXB，selectingOXB as a hydrophilic model drug, we designed the OXB ethosomal gel.Rats skin transdermal permeation in vitro shows that The cumulativepermeated percentage from ethosomal gel（4%OXB） is3.9times higherthan that from gel（10%OXB）; Rabbits pharmacokinetics in vivoindicates that the relative bioavailability of OXB ethosomal gel is293.7%compared with OXB gel. Skin irritation study shows that OXB ethosomalgel has no skin irritation.The results of these research present thatethosomes enhances transdermal penetrability significantly forOXB,which provide background for study on transdermal hydrophilicdrug delivery system.