Objectives: The objectives of the present investigation were to prepare recombinant human
insulin entrapped Eudragit-S100 microspheres containing protease inhibitors and to precisely
analyze the outcome of different formulation variables on the microspheres properties using a response
surface methodology to develop an optimized formulation with desirable features.
Methods: A central composite design was employed to produce microspheres of therapeutic protein
by w/o/w multiple emulsion solvent evaporation technique using Eudragit S-100 as coating material
and polyvinyl alcohol as a stabilizer. The effect of formulation variables (independent variables)
that is levels of Eudragit S-100 (X1), therapeutic protein (X2), volumes of inner aqueous phase (X3)
and external aqueous phase (X4) on dependant variables, that are encapsulation efficiency (Y1),
drug release at pH 1.2 after 2 h (Y2) and drug release at pH 7.4 after of 2 h (Y3) were evaluated.
Results: The significant terms in the mathematical models were generated for each response parameter
using multiple linear regression analysis and analysis of variance. All the formulation variables
except the volume of external aqueous phase (X4) exerted a significant effect (P <0.05) on
drug encapsulation efficiency (Y1) whereas first two variables, namely the levels of Eudragit S-100
(X1) and therapeutic protein (X2) materialized as the determining factors which significantly influenced
drug release at pH 1.2 after 2 h (Y2) and drug release at pH 7.4 after of 2 h (Y3). The formulation
was numerically optimized by framing the constraints on the dependent and independent variables
using the desirability approach. The experimental values for Y1 and Y2 of optimized formulation
were found to be 77.65% and 3.64%, respectively which were quite closer to results suggested
Conclusion: The results recorded indicate that the recombinant human insulin loaded Eudragit S-100
microspheres containing aprotinin have the benefits of higher loading efficiency, pH responsive and
prolonged release characteristics, which may help to carry insulin to the optimum site of absorption.