The influence of magnesium stearate on the characteristics of mucoadhesivemicrospheres

Microspheres containing the mucoadhesive polymer chitosan hydrochloride, wi th matrix polymer Eudragit RS, pipemidic acid as a moder drug and agglomera tion preventing agent magnesium stearate were prepared by the solvent evapo ration method. The amount of magnesium stearate was varied and the followin g methods were used for microsphere evaluation: sieve analysis, drug conten t and dissolution determination, scanning electron microscopy, xray diffrac tometry, DSC and FTIR spectroscopy. The results showed that average particl e size decreased with increasing amount of magnesium stearate used for micr osphere preparation. This is probably a consequence of stabilization of the emulsion droplets with magnesium stearate. Higher pipemidic acid content i n the microspheres was observed in larger particle size fractions and when higher amounts of magnesium stearate were used. It was also found that thes e two parameters significantly influenced the dissolution rate. The importa nt reason for the differences in drug content in microspheres of different particle sizes is the diffusion of pipemidic acid from the acetone droplets in liquid paraffin during the preparation procedure. The physical state of pipemidic acid changed from crystalline to mostly amorphous with its incor poration in microspheres, as shown by x-ray diffractometry and differential scanning calorimetry. No differences were observed in the physical state o f pipemidic acid and in microsphere shape and surface between different siz e fractions of microspheres, prepared with different amounts of magnesium s tearate. Additionally, no correlation between the physical state of the dru g in different microspheres and their biopharmaceutical properties was foun d.