Citric acid as a plasticizer for spray-dried microcapsules.

An aqueous spray-drying process was used to coat theophylline particles with a cellulose polymer, sodium carboxymethylcellulose (NaCMC) or hydroxypropylmethylcellulose (HPMC). Effect of a plasticizer, citric acid, was studied. Strength of cast films have a direct relationship to the dissolution T50% values of the respective spray-dried products. With varying plasticizer concentrations, changes in interaction between plasticizer and polymer, and in size of crystallized drug crystals, were observed with HPMC films. The plasticizer content also affected the films of NaCMC by bringing about a change in the form and arrangement of the drug. X-ray diffraction analyses of the different spray-dried products revealed a possibility of the predominance of different crystal forms. Spherical spray-dried microcapsules of NaCMC were formed with a 20-30% w/w plasticizer content. With HPMC, as plasticizer concentration was increased there was a corresponding increase in mean size of the spray-dried products. In terms of drug release and formation of spherical particles, a plasticizer concentration of 30% w/w was found to be suitable for both HPMC and NaCMC.