Preparation And Characterization Of W/O Microemulsion

When administered orally, Hydrophilic drug undergoes severe enzymatic degragation by gastric proteases and its high molecular weight renders it impermeable across gastric mucosa, limiting its overall bioavailability. Water in oil (W/O) microemulsion has a significant potential to increase permeability of hydrophilic drug across the intestinal mucosa and thus enhance their oral bioavailability. Using surfactants to stabilize microemulsions is associated with dosage limited in the food Field, this study aimed to screening optimal formula of W/O microemulsion, ensuring high drug loading and low surfactants content. The preparation of microemulsions using span80-tween80, PEG-7 hydrogenated castor oil and Labrasol-plurol diisostearique as surfactants and the effects of Km (the ratio of surfactant to cosurfactant) as well as the chain length of oil phase on microemulsion phase area were investigated. The structures of microemulsion, the effects of NaCl concentrations and temperatures on the microemulsions phase area were also examined. Also amino acids, peptides and proteins with different molecular weights and their associated effects on the phase behavior were evaluated. Hypoglycemic effects of insulin microemulsion, sustained release ability of 5-Fu microemulsion and the storage stability of the microemulsion were investigated.The results indicated that surfactants span80-tween80 and PEG-7 hydrogenated castor oil were suitable as hydrophilic drug carriers for preparation of W/O microemulsion and the optimum Km were 4:1 and 3:1, respectively. The optimal formula for preparation of W/O microemulsion was 61.6%, 26.3% and 12% of isopropyl myristate, mixed surfactants, and aqueous phase respectively. The conductivity, rheological properties and staining method showed that the three types of surfactants used all formed W/O microemulsions. Microemulsion phase area increased slightly as temperature increased and lowered when concentration of NaCl solution was elevated. The addition of amino acids, peptides and proteins with different molecular weight to the aqueous phase resulted in a regular change of phase area of microemulsion. While amino acids mainly through their effect on interface membrane formation influenced the microemulison phase area, peptide and protein did so through the viscosity of the aqueous phase of microemulsion phase area. The microemulsion phase area firstly showed both decreasing and then increasing trend when amino acids concentration increased in the aqueous phase. However, when peptide and protein concentration increased in the aqueous phase, the microemulsion phase area decreased. The comparison of the phase areas of microemulsions with different carbon chain showed that isopropyl myristate with medium carbon chain length was the most suitable oil phase for preparation of microemulsion. The particle diameter ranged from 10 to 30 nm and the Polydispersity index ranged from 0.08 to 0.40 which indicated that microemulsion had good uniformity and stability.The determination of blood glucose level of initial blood glucose level (BGL) after intake of insulin by experimental mice indicated that oral insulin exerted a significant hypoglycemic effect and when compared with those of control groups, the BGL of mice treated with the Span80-tween80 and PEG-7 hydrogenated castor oil microemulsions containing insulin was lowered by 183% and 151% respectively within 60 minutes. Hypoglycemic effect of oral insulin was enhanced with the entrapment of 1% (w/w) trypsin inhibitor and 3% (w/w) sodium taurocholate in aqueous phase. In the case of Span80-tween80 (HLB=6) microemulsion system, entrapment of 3% trypsin inhibitor in aqueous phase reduced the BGL of mice treated with insulin by 231% within 60 minutes.The sustained release test of 5-Fu mieroemulsion in the pH of simulated gastrointestinal tract environment indicated that Span80-tween80 and PEG-7 hydrogenated castor oil systems had a significant sustained release effect on 5-Fu. Span80-tween80 and PEG-7 hydrogenated castor oil systems gave total release rates of 59.6% and 77.83% in a simulated gastric juice and yielded 87% and 63.40% in a simulated intestinal juice after 20 hours, respectively. At the same time, the 5-Fu aqueous solution had a total release ratio of 90% after 20 hours. Entrapment of 1% NaCl in aqueous phase of Span80-tween80 system reduced the total release rate of 5-Fu in a simulated intestinal juice by 13.76% within 20 hours.The stability test indicated that microemulsions prepared by Span80-tween80 and PEG-7 hydrogenated castor oil had good stabilities and during storage process the particle diameter and polydispersity index showed no significant change. Multiple-layer and turbidity didn't appear in the microemulsions during two month storage at 0°C and 25°C or by centrifugation at 6000 rpm.