Abstract

The technique of three variables at three levels (33) factorial design was used to derive simple reduced second order polynomial equation for constructing contour plots to obtain predetermined percent drug entrapment within liposomes of idoxuridine prepared by reverse phase evaporation method. Three independent variables selected were volume of organic phase (x1), volume of aqueous phase (x2), and drug/phosphatidyichoIine/cholesterol in molar ratio (x3). Based on factorial design, twenty-seven batches of idoxuridine liposomes were prepared. Prepared liposomal batches were evaluated for size, lamellarity, and percent drug entrapment. The percent drug entrapment (dependent variable) and the transformed values of independent variables were subjected to multiple regression to establish a second order polynomial equation (full model). To simplify the equation, F-statistic was applied to reduce polynomial equation (reduced model) by neglecting insignificant (p>0.05) terms. The coefficient value for independent variable; drug/phosphatldy/choline/cholesterol in molar ratio (x3) was found to be maximum (b3=17.96) and hence the variable x3 was considered to be a major contributing variable for percent drug entrapment within liposomes prepared by reverse phase evaporation method. The reduced polynomial equation was used to plot three two-dimensional contour plots at a fixed levels of -1, 0 and 1 of major contributing variable (x3) to obtain various combinations of values of two other independent variables (x1 and x2) at predetermined percent drug entrapment. The conformity of the established equation was checked by preparing three batches three times taking values of the independent variables from the contour plots for prefixed value of percent drug entrapment. Prefixed percent drug entrapment values were taken for designing the experiment and results obtained experimentally were compared using student 't' test and difference between experimentally obtained and theoretically calculated values of percent drug entrapment was found to be statistically insignificant (p>0.05). Hence, finding of this study establishes the role of the derived equation and plotted contour plots in predicting the values of independent variables for preparation and optimization of idoxuridine liposomes by reverse phase evaporation method having predetermined percent drug entrapment.