| Tacrolimus(FK506),a 23-member macrolide antibiotic with strong lipophilicity,plays an important role in the treatment of autoimmune eye diseases,ocular allergic disorders and immune rejections after corneal transplantations.Its ophthalmic dosage forms marketed and intensively investigated are suspension drops,emulsions and colloidal particles,which have common limitations of low bioavailability and poor medical compliance.Those limitations are tried to be overcome in our designs by using pharmaceutics techniques to extend effect duration in eyes and enhance intraocular bioavailability of lipophilic tacrolimus.Objective: To prepare tacrolimus microemulsion and its ocular in-situ gelling delivery system successively,and to evaluate for their quality and safety.Methods:(1)Preparation of tacrolimus microemulsion.Effects of ingredients on the formation of microemulsion were studied by solubility test and pseudo-ternary phase diagram plotted from titration results.Formulation was optimized by central composite design-response surface method with microemulsion particle size,PDI and drug loading capacity as metrics.Effects of preparation process on microemulsion were investigated by single factor experiment.The drug loading determination of tacrolimus microemulsion by a high performance liquid chromatography(HPLC)was established.And its physiochemical properties were evaluated.(2)Preparation of tacrolimus in-situ microemulsion gels.The formulation to make tacrolimus microemulsion into thermosensitive in-situ ophthalmic gel was optimized by single-factor experiment and orthogonal experiment design using PE28 and PE8 as thermo-sensitive gel matrix and gelatinization temperature of in-situ gel before and after diluting in simulated tear fluid as compounding effect indicator.The appearance,particle size,morphology,gelation temperature,rheological characteristics,and in vitro dissolution and release behavior of the in-situ microemulsion gels were studied.(3)Residence time of tacrolimus microemulsion and its in-situ gels were examined using tacrolimus suspension eye drops as control.Irritation of ophthalmic microemulsion and its in-situ gels after single and multiple dose administrations were evaluated against normal saline as control by intra-individual self-control method with Draize test criteria.Results:(1)The O/W ophthalmic microemulsion containing 0.1% tacrolimus were prepared with 13 % Kolliphor EL(polyoxyethylene 35 castor oil)as emulsifier,5% Labrasol(caprylocaproyl polyoxyl-8 glycerides)as co-emulsifier,2% Labrafil M1944CS(oleoylmacrogol-6 glycerides)as oil phase,and double distilled water as aqueous phase.The emulsion droplets in elliptic shapes have an average particle size of 15.55 nm.The microemulation was tested to be at pH7.57 and 305 mOsm·Kg-1 in osmotic pressure.(2)The optimal formulation of in-situ microemulsion gels were composed of 14 % PE28 and 2 % PE8.The oval-shaped emulsion droplets homogenously disperse in in-situ emulsion gels with average particle size of 18.70 nm.Its gelation temperatures inside and outside eyes were 27.1 ?,33.9 ?,respectively.In vitro dissolution and release tests showed that its releasing characteristics follow zero-order kinetics.(3)Residence time of tacrolimus microemulsion and its in-situ gel in rabbit eyes were 15.33 min and 22.67 min respectively,while 15.67 min for suspension drops.No irritation was found for tacrolimus suspension drops,microemulsion and its in-situ gel.Conclusion: It would be feasible to prepare tacrolimus temperature-sensitive in-situ gel from microemulsion with a simple preparation process.The gels were of controllable quality,good stability and low eye irritation.Compared with suspension eye drops,in-situ microemulsion gels of tacrolimus can be expected to be a superior ophthalmic drug delivery system for hydrophobic drugs due to its steady and sustained release characteristics. |
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