Abstract
Purpose: To formulate theophylline microspheres with cellulose
acetate using solvent evaporation method and evaluate the effect of
various processing factors on their characteristics. Methods:
Microspheres containing theophylline were prepared with a hydrophilic,
biocompatible polymer -cellulose acetate -by an emulsion solvent
evaporation technique using an acetone/liquid paraffin system
containing Span 80 as a surfactant. The effect of processing factors,
e.g., varying drug/polymer ratio (1:1, 1:2, 1:3) and temperature (10
and 35°C) on microsphere characteristics and drug release were
examined. Similarly, microspheres with a drug/polymer ratio of 1:3
incorporating Span 20 were also also prepared and evaluated. Results:
The microspheres were white, free-flowing and spherical. The yield
varied from 73.0 to 87.5 % while entrapment efficiency was in the
region of 71.8 to 92.4 %. High drug/polymer ratio, Span 80 (surfactant)
and processing temperature between 10 and 30°C produced
formulations with better drug entrapment efficiency. High drug/polymer
ratio, low processing temperature and low HLB value of surfactant
enhanced the sustained drug release characteristics of the
microspheres. Conclusion: The combination of three suitable factors
-Span mixture (with HLB value of 4.3), processing temperature of 10
°C and drug/polymer ratio of 1:3 -produced a suitable controlled
release theophilline microsphere formulation which could be effective
for the management of asthma.