Preparation and Evaluation of Dual Modified Ethiopian Yam (Dioscorea abyssinica) Starch for Sustained Release Tablet Formulation
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Date
2013-01
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Addis Ababa University
Abstract
Starch has been the subject of intensive research over many decades due to the fact that native starches are diverse, biodegradable, applications are enormous and modifications to starch are numerous. In this study, Dioscorea abyssinica (boyna) starch has been chemically modified with the aim of determining its potential for sustained release application. It was chemically modified by cross-linking using sodium hexametaphosphate (SHMP), acetylating with acetic anhydride and dual modified - cross-linking followed by acetylation. Cross-linked starches (CLSs) with degree of cross-linking (DC) of 54.46, 62.20 and 68.88 (%), CLS-A, CLS-B, CLS-C respectively, were obtained while cross-linking the native starch (NS) with 5, 10, and 15% SHMP for 6 h. By reacting boyna starch with acetic anhydride (AA) in ratios of 1:1 and 1:2, starch acetates (SAs) with degrees of substitution of 0.339 (SA-A) and 0.546 (SA-B), were obtained, respectively. In an attempt to prepare a dual modified starch (DMS), the CLSs were acetylated in a similar condition as the NS. The physicochemical, material, and tablet forming properties of the modified starches were investigated to determine potential usages in sustained release applications. In moisture sorption study, CLSs exhibited the lowest water-uptake and SAs notably increased the sorption capacity of the NS and CLS. Cross-linking decreased the swelling power of the NS as the level of SHMP was increased while acetylation showed the opposite effect. The reduction observed in viscosity values indicated the effectiveness of cross-linking in reducing swelling of the NS. On the basis of powder properties analyses, it was evident that acetylation improved the poor flow properties of CLSs and NS. SAs were found to be free flowing with angles of repose of 25.11O and 23.02O and flow rate of 3.09 and 10.54 g/sec, respectively for SA-A and SA-B. The Hausner ratio of the SAs was 1.18 and 1.25 and Carr’s index of 22.36 and 20.24, respectively for SA-A and SA-B. Tablets were prepared and evaluated for hardness, tensile strength, friability, and disintegration time. Results indicated that both cross-linking and acetylation processes improved tablet forming properties of the NS with more significant effect in the dual modified starches. The Fourier transform infrared (FTIR) spectra revealed that a structural change occurred in the NS because of cross-linking and acetylation. Correspondingly, the spectral analysis proved that the dual modified starches are compatible with theophylline.
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Dissolution studies of theophylline loaded modified starches were performed for 12 h. Matrix tablets containing Ac-CLS-F, where CLS-C reacted in a 1:2 ratio with AA, loaded with 20, 30 and 40% theophylline and Ac-CLS-E, where CLS-C reacted in a 1:1 ratio with AA, loaded with 20% theophylline were studied for drug release. And 80% of theophylline was released in about 10.62, 9.35, and 8.18 h from 20, 30 and 40% theophylline loaded Ac-CLS-F, respectively, whereas 20% theophylline loaded Ac-CLS-E released its drug content within about 12 h of the dissolution study. The dissolution data was subjected to the various drug release kinetic models and the data best fitted Higuchi model with R2 > 0.994. The drug release diffusional exponent (n), with goodness of fit > 0.988 obtained for Korsemeyer-Peppas model for 20, 30 and 40% drug loaded Ac-CLS-F varied between 0.452-0.530 indicating deviation from Fickian diffusion mechanism whereas a quasi-Fickian diffusion behavior was exhibited (n = 0.31) for 20% loaded Ac-CLS-E. From the foregoing, it can be concluded that Ac-CLS-F could have a potential for use as a sustained release excipient.
Key words: Dioscorea abyssinica, Boyna starch, Cross-linking, Acetylation, Dual modification, Sustained release.
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Keywords
Dioscorea abyssinica; Boyna starch; Cross-linking; Acetylation; Dual modification; Sustained release