Drug release from starch-acetate microparticles and films with and without incorporated α-amylase

Acetylation of starch considerably decreases its swelling and enzymatic degradation. Thus, starch-acetate (SA) based delivery systems may be suitable for controlled drug delivery. The aim of the present study was to evaluate drug release from the SA microparticles (SA mps) and SA films. The average degree of acetyl substitution (DS) per glucose residue in the starch was either 1.9 (SA DS 1.9) or 2.6 (SA DS 2.6). Timolol (mw 332), calcein (mw 623) and bovine serum albumin (BSA, mw 68,000) were used as model drugs. A continuous timolol release from the both SA mps was observed in phosphate buffer solution (PBS) pH 7.4 (50-days incubation). The release of timolol was faster from the SA DS 1.9 mps than from the SA DS 2.6 mps. Calcein release from both SA mps was continuous in PBS pH 7.4 (5-days incubation). But, calcein release profile from the SA DS 2.6 film in PBS pH 7.4 showed discontinuities. However, the release of calcein from both SA films was continuous in human serum in vitro during the 7-day incubation, i.e. enzymes enhanced calcein release. Thus, α-amylase was incorporated into the SA films in order to enhance drug release from the films. However, the effects of incorporation of α-amylase on the model macromolecule (BSA) release from the SA films were modest. In conclusion, this study demonstrates the achievement of slow release of different molecular weight model drugs from the SA mps and films as compared to fast release from the native starch preparations. DS of SA, physicochemical properties of a drug and the presence of enzymes can all affect drug release profiles from SA based preparations.