The effect of pharmaceutical excipients on isoniazid release from chitosan beads
Van Rensburg, Andries Gideon
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In controlled release applications a drug is molecularly dispersed in a polymer phase. In the presence of a thermodynamically compatible solvent, swelling occurs and the polymer releases its content to the surrounding medium. The rate of the drug release can be controlled by interfering with the swelling rate of the beads or by influencing diffusion through the viscosity of the polymer. Beads that contain chitosan were prepared through the ionotropic gelation method where tripolyphosphate (TPP) was used as the crosslinking agent. Beads that consisted of 3% w/v isoniazid (lNH) and 5% w/v chitosan were prepared in a 5% w/v TPP solution (pH 8.7) as the primary beads. To improve the drug loading of chitosan isoniazid beads (ClB) the TPP concentration, pH of the TPP solution and the INH concentrations were altered for maximum drug loading. To increase the porosity of the beads of chitosan beads Explotab® (EXPL), Ac-Di-Sol® (ADS) and Vitamin C (VC) were added individually to chitosan solutions at concentrations of 0.1, 0.25 and 0.5% w/v before adding the mixture to the TPP solution. Morphology, swelling and drug loading studies were used to evaluate the different formulations. After these excipients were added individually they were also added in combinations of two excipients respectively and characterised. From the results of the drug loading studies the beads that contained only chitosan and isoniazid showed a percentage drug loading of (43.92%) which is the best of all the beads that were analyzed. The multi excipient combination of Ac-Di-Sol® and Explotab® showed the best swelling capability at both pH levels. Dissolution studies were conducted on all the formu lations over a period of 6 hours (360 minutes) at pH 5.6 and pH 7.4. From the dissolution results it were clear that no chitosan dissolved at both pH values. The dissolution of single pharmaceutical excipient (SPE) and multi pharmaceutical excipient (MPE) formulations can be arranged in the following order: VC/ADS < VC < ADS/EXPL < ADS < VC/EXPL < CIB < EXPL. Explotab® is a potential excipient for enhanced drug release over a wide pH range.
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