title: Comparison of microencapsulation by emulsion-solvent extraction/evaporation technique using derivatives cellulose and acrylate-methacrylate copolymer as carriers.
abstract: BACKGROUND
  Microencapsulation is a useful method to prolong a drug release from dosage forms and to reduce its adverse effect (1) among various available methods. The microencapsulation of hydrophilic active ingredients requires the use of a polar dispersing phase such as a mineral oil. Acetone/paraffin systems are conventionally used.
  
  
  OBJECTIVE
  The current study aimed to investigate two different microencapsulation techniques comparatively, water in oil in oil (w/o/o) and oil in oil (o/o), for theophylline (TH) loaded ethylcellulose (EC), cellulose acetate butyrate (CAB), Eudragit RS and RL microspheres with regard to loading efficiency, release and degradation kinetics.
  
  
  METHODS
  Microspheres were prepared by the emulsification method by solvent diffusion/evaporation technique and different polymers which were incorporated into microspheres to control the release rate of drug. Theophylline (TH) was chosen as a model drug. The emulsion technique was investigated for to prepare theophylline microparticles. EC and CAB and acrylatemethacrylate copolymer corresponding to the above ratios were selected as microparticles wall materials. The effects of type polymers on the physical characteristics and dissolution of the microparticles were also studied. However, the TH loading efficiency (for w/o/o emulsion about 90.64% and o/o emulsion about 73.90/5 to 95.90%) and the TH release kinetics were influenced by the microencapsulation technique.
  
  
  RESULTS
  The results demonstrated that the o/o microspheres (containing of CAB) was most appropriate, providing a high encapsulation efficiency (95.90%) and low initial burst release (6.45%). The microspheres prepared with CAB polymer showed faster dissolution rate than other polymers with 0.75: 1 drug to polymer ratio. The double emulsion technique with EC as wall material gave the high dissolution efficiency (80.48%) of microcapsules.
  
  
  CONCLUSIONS
  Eudragit RS microspheres showed higher yield (90%). The release of TH from CAB and Eudragit RL walled microcapsules was slow whilst the release from those of EC and Eudragit RS were faster. The type of polymer and the drug to polymer ratio were found to be the key factors affecting the release profile which could lead to microspheres with desired release behavior.
authors.affiliation: School of Pharmacy, Tabriz University of Medical Sciences, Tabriz, IR Iran ; Drug Applied Research Centre and Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, IR Iran.
authors.forename: Mitra
authors.initials: M
authors.lastname: Jelvehgari
authors.affiliation: Islamic Azad University of Bonab Unit, Bonab, IR Iran.
authors.forename: Seyed Hassan
authors.initials: SH
authors.lastname: Montazam
keywords: Copolymer; Drug Carriers; Drug Componding