Abstract
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. 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. 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. 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. 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.
Highlights
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 results suggest that the single emulsion technique (O/O) is suitable for preparation of TH-loaded Eudragit RS, RL and cellulose acetate butyrate (CAB) microspheres
The in vitro release profiles were fitted on various kinetic models in order to find out the mechanism of drug release [17, 18]
Summary
Microencapsulation is a useful method to prolong a drug release from dosage forms and to reduce its adverse effect [1] among various available methods. Materials and 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. Incorporation levels of the hydrophilic active ingredient into the microspheres related to the amounts employed in the process are fairly low and, this system involves a limitation with respect to the types of polymers which may be used, given that it requires the polymer to be soluble in acetone dispersing phase [2]. Further innovative methods have been proposed for the efficient encapsulation of water soluble drugs by the emulsion solvent evaporation technique involving double emulsion (multiple emulsions) formation where an aqueous core material solution is emulsified in a polymer volatile organic solvent solution. Since the external phase is an organic solution, there is no problem as mentioned in w/o or o/o method
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