Development Of Apremilast Microemulsion-based Gel

The past few years has witnessed gradual increase in the incidence of psoriasis in our country.Etiology of psoriasis is very complex,involving autoimmunity,psoriasis-related susceptibility genes,autoantigen and a variety of environmental factors.Psoriasis is an incurable chronic inflammatory disease of long course that can severely affect the physical and mental health of the patients.Its major clinical manifestations are erythema and scales;its basic pathological features are excessive proliferation of epidermal cells and parakeratosis.According to recent research,psoriasis is a T-cell mediated immune disease in the context of polygenic inheritance.Apremilast（APL）is developed by Celgene Corporation,the U.S.gene biotechnology company.APL was FDA approved in 2014 for use in treating psoriatic arthritis（PsA）in adults and moderate-severe plaque psoriasis.The drug is the first oral medication approved for treating psoriasis over the past 20 years,and also the first oral medication approved for treating PsA over the past 15 years.Currently,there are only oral tablets on the market.However,such tablets are found of poor bioavailability,inevitable first-pass effect of liver and gastrointestinal side effects.This research plans to make APL into microemulsion-based gel（MBG）to apply to local affected parts directly.In this way,it may overcome the disadvantages of general application,reduce its side effects and improve patient compliance.Microemulsion（ME）is a transparent or slightly opalescent colloidal dispersion system formed spontaneously by water,oil,emulsifier and co-emulsifier in appropriate proportion.ME can well dissolve water-soluble and lipid-soluble drugs and those hardly soluble in both water and oil and can enhance the solubility of poorly soluble drugs and the stability of soluble drugs.It is suitable for oral,intramuscular and transdermal administration.APL is very difficult to dissolve in water.Making it into ME preparation can increase its solubility,improve its bioavailability and thus enhance its efficacy.This research introduces pseudo-ternary phase diagram to locate the emulsion forming areas of ME and roughly determine the content of the components.The experiment is designed with simplex lattice design（SLD）,with the content of ME components as independent variables and drug loading and average particle size as dependent variables to obtain the theoretically optimal prescription.Based on in vitro percutaneous absorption test and drug dermal retention,the optimal ME prescription is determined as:mixed emulsifier 58.6%（Brij-C20:Tween-80:Transcutol-p=1:1:4）,water 24.7%,oil glyceryl triacetate 16.7%.ME prepared by the optimal prescription is regularly spherical under transmission electron microscope（TEM）,average particle size being 20.30nm.For ease of use,ME is mixed with 1.5%carbomer gel matrix in 1:2,and its pH adjusted to 6.5-7.0 using triethanolamine,thus producing the APL MBG.In this way,the formulation and preparation process of APL MBG are determined.In vitro percutaneous penetration test showed that the cumulative permeation of APL MBG was significantly higher than that of general gel.The percutaneous permeation test of 12h showed that the cumulative permeation of apposition microemulsion gel was 3.3 times of that of genera gel,and the drug retention of apposition microemulsion gel in skin was 12.5 times that of general gel in drug dermal retention.In vivo transdermal permeation experiments in mice showed that the concentration of APL in plasma,the concentration of microemulsion in plasma was 13.90 g/ml,and the concentration of microemulsion in plasma was 5.09 g/ml.In the drug dermal retention,the drug concentration in the skin of microemulsion preparation was 5.38 g/ml,and the concentration of microemulsion gel in skin was 13.34 g/ml.Microemulsion gel forms a drug pool in the skin,so that the concentration of the drug in the skin is much larger than that in the plasma,thereby reducing the dosage and reducing the adverse reaction.According to skin irritation test,APL MBG has no irritating effect on the skin of guinea pigs despite of the times of administration.In the pharmacodynamics experiment,the APL MBG can obviously alleviate psoriasis like skin morphology in psoriasis mice,and the scales,thickening and erythema are relieved obviously.The PASI score of psoriasis was reduced;Microscopic observation after he staining of tissue sections showed that the pathological phenomena such as incomplete keratosis,epidermal hyperplasia,inflammatory infiltration and hyperkeratosis were significantly improved;Immunohistochemistry showed that the expression of T cells and neutrophils decreased significantly,and the inflammatory response decreased significantly;ELISA also showed that inflammatory factors IL-17,IL-23 and TNF-α APL MBG shows good therapeutic effect on the mouse model of imiquimod-induced psoriasis.