Background: There are conflicting reports regarding the effect of polymer viscosity grade on
microcapsule properties. The aim of the present study was to investigate the effect of just viscosity
grade of ethylcellulose (EC) (not polymeric solution) on properties of theophylline microcapsules prepared
by emulsion solvent evaporation.
Methods: The effect of EC viscosity grade and drug:polymer ratio was investigated on microcapsule
properties (yield, particle size, morphology, surface characteristics and drug release). Differential scanning
calorimetry (DSC) and X-ray powder diffraction (XRD) were implemented to study the interaction
and solid state of drug. The microcapsules were compressed in the presence of excipients and drug release
Results: The yield of microencapsulation and encapsulation efficiency at 1:1 drug:polymer ratio was
dependent on EC viscosity. Microcapsules were spherical with some pores on their surfaces. The number
of pores was more and their size was bigger for EC 100 cP microcapsules. Theophylline remained in
crystalline form after encapsulation. DSC studies confirmed lack of interaction between drug and polymer.
The drug release was rapid at 2:1 drug:polymer whilst it was slowed down at 1:1 drug:polymer ratio.
Microcapsules obtained from EC 100 cP showed slightly faster drug release at latter ratio. Marginal
changes in release rate were observed after compression of microcapsules.
Conclusions: All viscosity grades of EC were able to sustain the release of the drug from microcapsules.
Considering the similar release profiles for microcapsules prepared from different viscosities of
EC, the use of lower viscosity grade of EC is recommended due to the ease of production and also less