In vitro-in vivoevaluation of bacampicillin hydrochloride from microcapsules of a water-insoluble and an acid-soluble polymer

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Abstract
Bacampicillin hydrochloride has been microencapsulated to mask its very bitter taste. The objective of the study was to compare the in vitro release and bioavailability of bacampicillin hydrochloride from microcapsules coated with two principally different polymers: a water-insoluble polymer, ethylcellulose, and an acid-soluble polymer, Eudragit® E 100. The last mentioned was supposed to have advantages from a bioavailability point of view since this polymer should dissolve rapidly upon reaching the stomach. In vitro release studies were performed in different types of media by using a flow-through cell technique and USP paddle apparatus. The in vivo study was performed on 20 healthy volunteers taking single 400 mg doses of the drug in the two microcapsule suspensions and a reference tablet according to a randomized cross-over design. When standard dissolution fluids were used, the Eudragit® E 100-coated microcapsules revealed very rapid dissolution but were greatly dependent on buffer concentration and ionic strength. The ethylcellulose-coated microcapsules released the drug much more slowly than Eudragit® E 100 when using standard dissolution fluids. They were also affected by buffer concentration and ionic strength. The reference tablet had a significantly higher bioavailability than the two microcapsule suspensions. In vitro-in vivo correlation was not obtained when using standard dissolution fluids according to USP. However when simulated intestinal fluid was adjusted to have an ionic strength similar to intestinal fluid, a better in vitro—in vivo correlation was obtained. The Eudragit® E 100 polymer did not give better bioavailability than ethylcellulose as a coating polymer on bacampicillin microcapsules.