Influence of polymers weight ratio and pH of polymers solution on the characteristics of chitosan-carboxymethyl cellulose microspheres containing theophylline.

Optimization of formulation for chitosan-carboxymethyl cellulose (CH-CMC) microspheres that contain a drug of narrrow therapeutic index was the interest of this study. Theophylline (TPH) was chosen as a model drug. The effects of chitosan:sodium carboxymethyl cellulose (CH:SCMC) weight ratio (X1) and pH of polymers solution (X2) as independent variables on the physical characteristics of the microspheres as well as release profile of TPH from microspheres prepared by the emulsion coacervation-phase separation technique were studied. The influence of each of the two variables on responses such as angle of repose, compressibility index, incorporation efficiency particle size, initial drug release, time for 50% drug release (T50%) and % drug released in 8 hours was investigated. Generally, the increase in CH:SCMC weight ratio showed to increase the incorporation efficiency of the drug, increase the particle size and decrease the flowability of the microspheres. The increase of CH:SCMC ratio was also responsible to get low initial drug release, slow drug release (long T50%) and incomplete total drug released in 8 hours. On the other hand, high and low pHs of polymers solution were responsible to decrease drug incorporation in the microspheres and to produce small particles while, good flowability was obtained at pHs 2.5 and 4. A full factorial experimental design was employed to investigate the effect of the two independent variables on the responses. The results were analyzed by a general quadratic equation and response surfaces generated. From the obtained regression, it was concluded that the effect of CH:SCMC polymers ratio is more significant in changing the values of flowability particle size and drug release in 8 hours while pH values were more significant in changing the values of initial drug release and T50%. On the other hand the interaction coefficients of the two variables showed synergistic effect on flowability and drug release in 8 hours while, there were antagonist effects on particle sizes and T50%. From the optimization studies it is possible to choose the conditions required for the preparation of microspheres with the desired characteristics.