Bioavailability Enhancement

Thairs et al. [16] examined the effect of dose, food and coating of an ion-exchange resin on its gastric residence time and distribution after ingestion. Using scintigraphy, they showed that approximately 20% of the resin persisted in the stomach for the

Drug release of risperidone from [a] Physical mixture 1:1 (•) & complex 1:1 (o),[b]Physical mixture 1:2 (a) & complex 1:2 (a), [c] Physical mixture 1:4 (■ ), & complex 1:4 (□ )and [d] Physical mixture 1:6 (♦ ) & complex 1:6 (o)

Fig. 8.5 Drug release of risperidone: effect of resinate formation. Reprinted from [15]

entire 6 h of study and in all cases the resin was distributed evenly throughout the fundus, body and antrum of the stomach. Gastric retention was also longer with resin particles without polymer coating. Dose and food had insignificant effects on gastric residence time.

Cuna et al. [17] prepared amoxicillin-loaded ion-exchange resinate, encapsulated in mucoadhesive polymers (polycarbophil and Carbopol 934) to achieve increased efficacy of amoxicillin in peptic ulcer treatment by targeted delivery to the gastric mucosa and prolonged drug release at the site. Fluorescence microscopy indicated that gastric residence time and distribution of particles on the mucosa was better for nonpolymer-coated particles. While there was no ready explanation for the mechanism for increased gastric residence time and/or mucoadherence, the findings suggest that there may be opportunities for formulating drug molecules having "absorption windows" by increasing the gastric retention time with resinates, to provide better or more complete absorption. Another possibility would be to target drug delivery to treat gastric disease, for example gastric reflux caused by H. pylori.

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