Preparation of sustained release theophylline by using different techniques

ABSTRACT

Sustained release theophylline has been prepared by using the solid dispersion, wet granulation and microencapsulation techniques. Physical mixture of the drug and ethyl-cellulose showed complete drug release within 80 minutes, a fact that excludes their application in controlling drug release. Co-precipitates of theophylline in ethylcellulose [EC] were prepared using different concentrations of the polymer dissolved in ethanol or in ethanol-chloroform mixture [11]. The dissolution studies showed that the concentration of the polymer in the system is a determining factor in controlling the release rate of the drug. The type of solvent also has a marked effect on the rate and pattern of theophylline release. Within half an hour, 32.4% of the drug was released from the solid dispersion prepared using ethanol alone and T50 was 45 minutes, while only 20.9% of the drug was released from the solid dispersion prepared using a mixture of solvents and T50 was 180 minutes. The presence of polyvinyl-pyrrolidone [PVP], modified the release pattern of theophylline. The results showed that by increasing the PVP/EC ratio, the rate of theophylline release increased. Theophylline granules were prepared using different amounts of microcrystalline cellulose, cellulose acetate phthalate and ethylcellulose as fillers. The obtained dissolution results showed that altering the Avicel-ethylcellulose ratio affected the release rate markedly. Theophylline microcapsules showed initial rapid release where about 40% of the core was released within one hour. The obtained results revealed that co-evaporates could be considered as an ideal technique for preparing medicines required for sustained release preparations. This is due to the homogeneous drug distribution and the uniform drug release in comparison to the other techniques used in this study