Study On Naltrexone-loaded PLGA Microspheres Prepared By A Microreactor Technology

Naltrexone is a non-selective,high-affinity opioid receptor antagonist.Its pharmacodynamics are similar to that of naloxone.Naltrexone can relieve physical dependence on opioids and enable abstinent opioid addicts to maintain a normal life without physical or mental dependence.Naltrexone was approved by FDA for the treatment of opioid dependence in 1985,and for the treatment of alcohol dependence in 1994.At present,naltrexone is mainly marketed as tablets,but the half-life of the drug is short because it is easy to be degraded in vivo.Therefore,it is necessary to extend the action time of the drug to reduce the frequency of administration,so as to solve the problem of poor patient compliance.As a new drug carrier,microspheres can improve drug stability,control drug release rate,prolong drug action time,improve efficacy and reduce side effects.However,the traditional method for the preparation of microspheres has some shortcomings,such as poor reproducibility,difficulty in scale-up,low preparation yield and complex parameter control,which hinder the industrialization development of microspheres.Therefore,in order to overcome the shortcomings of the traditional method,novel microreactor technology was used for the preparation of naltrexone-loaded PLGA microspheres with easy scale-up,high batch reproducibility,simple preparation process and high quality assurance.(1)Preformulation study.The high performance liquid chromatography(HPLC)method of naltrexone was established.The solubility of the drug at different pH media was determined.The established HPLC method showed a good linear relationship,high precision,good recovery and high stability.It was suitable for in vitro drug analysis and quality control.The solubility of drug is high in acidic media and low in neutral and alkaline media.(2)Formulation and preparation process of naltrexone-loaded PLGA microspheres using traditional methods.Naltrexone-loaded PLGA microspheres were prepared by two traditional methods(including emulsion evaporation and phase separation).The formulation and preparation process were optimized in terms of particle size,surface morphology,encapsulation efficiency(EE)and in vitro release.The phase separation method is not suitable for the preparation of naltrexone microspheres because of its low encapsulation efficiency and poor appearance.The molecular weight and concentration of PLGA,the ratio of oil phase/water phase/solidification phase,and the percentage of emulsion evaporation significant affected on the EE and drug release of microspheres.The optimal formulation and preparation conditions were as follows(Fee-59):The oil phase was 10%PLGA dissolved in dichloromethane.The ratio of PLGA(Mw=12 kDa)to PLGA(Mw=150 kDa)was 1:3,and the aqueous phase was 1%PVA solution.The two phases were stirred and mixed to form a raw emulsion.After evaporating 13%organic solvent,the raw emulsion was transferred to water for solidification.The ratio of oil phase/water phase/solidification phase was 1:5:125(v/v/v).The resulting microspheres were washed and then freeze-dried.(3)Formulation and preparation process of naltrexone-loaded PLGA microspheres using a microreactor technology.Naltrexone-loaded PLGA microspheres were prepared by a microreactor technology.The formulation and preparation process were optimized in terms of particle size,surface morphology,encapsulation efficiency(EE)and in vitro release.The results showed that the molecular weight and concentration of PLGA,the ratio of oil phase/water phase/solidification phase,the percentage of emulsion evaporation,the flow rate of oil phase and water phase,and the pressure of emulsion evaporation have significant effects on the properties of microspheres.The optimal formulation and preparation conditions were as follows(Fmr-43):The oil phase was 10%PLGA dissolved in dichloromethane.The ratio of PLGA(Mw=12 kDa)to PLGA(Mw=150 kDa)was 1:4.The water phase and oil phases were mixed by a microreactor.The flow rates of oil phase and water phase were 15 and 45 mL/min,respectively.After 20%organic solvent was evaporated from raw emulsion under the condition of reduced pressure 440 mmHg,the resulting emulsion was transferred to water for solidification.The ratio of oil phase/water phase/solidification phase was 1:3:75(v/v/v).The resulting microspheres were washed and then freeze-dried.(4)In vitro evaluation of naltrexone-loaded PLGA microspheres.Three batches of optimized formulations(Fmr-43-1,Fmr-43-2 and Fmr-43-3)were studied.The particle size of three batches was in the range of 63-100 μm.Encapsulation efficacies of three batches were 82.33±1.32%,86.47±1.58%and 83.73±1.04%,respectively.The in vitro accelerated release curve was similar to that of original product(Vivitrol(?)),with f2 similarity factors of 60.64,52.91 and 61.79,respectively.The residual dichloromethane in drug-loaded microspheres were analyzed using a gas chromatography.The contents of residual solvents of the three batches were 0.8446%,1.0658%and 0.9952%,respectively.The physicochemical properties of the naltrexone-loaded PLGA microspheres were characterized by X-Ray Powder Diffraction(XRD),Differential Scanning Calorimetry(DSC)and Fourier transform infrared spectroscopy(FT-IR).The results showed that the crystal state and melting point of the drug had changed,and some molecular interactions occurred between the drug molecule and PLGA.(5)Pharmacokinetic studies of naltrexone-loaded PLGA microspheres.The HPLC method for the determination of naltrexone in rabbit plasma was established.The drugloaded PLGA microspheres were administered through an intramuscular injection to rabbits.Blood samples were collected from the ear vein on 0,1,2,3,4,5,6,7,14,21 and 28 days.The plasma drug concentration-time curves of various microspheres(Fmr-18,Fmr-43,and Fmr-45)were compared,and the pharmacokinetic parameters were calculated.The results showed that the drug concentration-time curves and pharmacokinetic parameters(Cmax,Tmax,AUC)of three batches were significantly different compared with each other.(6)Preliminary study of accelerated stability.The preliminary stability study of microspheres was conducted under temperature(4℃,25℃ and 40℃),humidity(RH 75%,RH 92.5%)or light(4500 lx)for 10 days.It turned out that high temperature,high humidity and strong light had significant influence on the surface morphology,drug content and in vitro release of microspheres.In conclusion,naltrexone-loaded PLGA microspheres were successfully prepared using a microreactor technology with a suitable particle size,round shape,high encapsulation efficiency and sustained release in vitro and in vivo.This study can provide a basis for the industrial production of naltrexone-loaded PLGA microspheres.