Paclitaxel Submicron Emulsion Injection

Paclitaxel(PTX)with a wide spectrum of activity against solid tumors has been widely used clinically all over the world and proven to be one of the most broadly effective anticancer agents.However,because the commercially available injection is a sterile solution of the drug in Cremophor(?)EL(polyethoxylated castor oil)and dehydrated alcohol,paclitaxel therapy is associated with life-threatening hypersensitivity reactions,and there is a danger that paclitaxel may crystallize during the process of dilution.Thus,the aim of this study was to prepare and evaluate a Cremophor(?)EL free paclitaxel sub-microemulsion injection(PSME).An HPLC method was established for the assay of PSME,the method validations were carried out and approved.PTX is a highly lipophilic drug(Ko/w =311),and has the best solubility in dl-α-tocopherol.The solubility ofpaclitaxel in triglyceride decreases as the length of the aliphatic chain increases.The degradation rate constants of PTX in pH4.0,5.0,5.5,6.0 PBS at 80℃were similar.The degradation rate constant of PTX in pH5.5 was the lowest,and the corresponding t_1/2was the longest(19.31 hours).Because PTX-loaded sub-microemulsions containing dl-α-tocopherol have been reported to have great advantages and the product TOCOSOL(?)has completed its valuable phaseⅡclinical trails,dl-α-tocopherol-based paclitaxel sub-microemulsion was firstly designed and prepared. High pressure homogenization method was used to prepare TPSME.The physicochemical properties(such as:appearance,particle size,zeta potential,drug entrapment efficiency,content) were select as the indexes to evaluate and optimize the formulation and preparing process of TPSME.The TPSME product could maintain stable for 6 months at 6±2℃.However,guinea pigs were found to die within 48h after i.v.administration of TPSME at a dose of 5.4mg/kg,and dl-α-tocopherol was inferred as the cause.Thus,we gave up the TPSME,and started to prepare and evaluate paclitaxel sub-microemulsion withoutα-tocopherol,named PSME.High pressure homogenization method was used to prepare PSME.The final formulation and preparing process of PSME were as follows:Pluronic F68 0.2%,Tween80 0.2%,glycerol 2.5%and EDTA-2Na 0.02%were dissolved in water for injection stirring at 75℃to obtain a water phase.Meanwhile,paclitaxel 0.06%,soybean lecithin 3%,MCT 15%,and oleic acid 0.05%were co-dissolved in ethanol with stirring at 75℃in a water bath,then the ethanol was removed by evaporation under a stream of nitrogen,and a clear oil phase was obtained.The oil phase was added to the water phase and mixed using a high-shear mixer at 10000 rpm to prepare the primary emulsion.After adjusting the pH to about 5.5 with 0.1 mol/1 HCl or NaOH solution, the primary emulsion was passed through a high pressure homogenizer(800 bar,10 cycles). Finally,the product was gassed with N₂ and sealed in 50 ml glass bottles followed by sterilizing in a rotating water bath at 100℃for 45 min.Three batches of PSME were prepared to study their stability.The physiochemical characters such as appearance,particle size,zeta potential,drug entrapment efficiency,content, related compounds,free fatty acid were evaluated in detail.The PSME could maintain stable for 10 days at 60℃,6 months at 25±2℃,and 12 months at 6±2℃.The commercial paclitaxel injection was used as a reference to evaluate the pharmacokinetics and tissue distribution of PSME.The PSME had similar pharmacokinetic characteristics comparing with the commercial paclitaxel injection.The pharmacokinetic data obtained with both preparations fitted a two-compartment model(weight 1/C).The AUC_0-12hof PSME and PTX injection were 7.771±1.384μg·mL^-1·h and 7.052±2.023μg·mL^-1·h respectively, and the ratio of them was 1.11.The relative tissue exposure values(r_e)of liver,spleen,lung, kidney were 1.25,1.28,1.24 and 1.33 separately.So there is only a little accumulation of PSME in liver(25%),spleen(28%),lung(24%)and kidney(33%).The PSME did not cause obvious tissue distribution changes of paclitaxel in rats.The safety test was carried out to evaluate PSME.The results indicated that the PSME did not cause any hemolysis;the PSME did not cause any irritation to rabbit ear-rim auricular vein; the PSME did not cause any hypersensitivity reactions or toxicity in guinea pigs.